Long Range Tank Gunnery -- Again

[jwduquette1]

could this be modeled with my naval ballistics program?

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Ultimately the interest here is inherent Shot dispersion.

[nigelfe]

The reason why I think chg S is a better comparison is that its MV and max range are closer to 88mm. As I said in my first post on this I think 88mm max rg s2s was 14+ km. The point is that dispersion tends to increase as max range is approached, therefore if you compare at a range that is max rg for one gun and 80% max for another you don't get comparable figures. The 25 pr chg S figures are clear, at 1 km its 30 vs 69, at 10 km 80 vs 75. Howver in actually the 25 pr figures could be anywhere between 26 & 34 or 76 & 84. This rounding was standard practice for PE in WW2 and even when they issued mils/metres RTs in 1967 they still used the rounded figures.

 

There are several reasons for the changes to 25 pr RTs, the first edn was for the Mk 1 carriage, which had some limitations. Then they introduced new varieties of ammo, and there were probably changes in fze wts as 117 evolved. Also need to compare the driving band patterns, although by WW2 these were fairly stable. Then there's the propellant varieties, as 175 mm shows (if you believe the FT) this can have some odd effects, although its difficult to pin down a cause and theoretically probably shouldn't happen. Of course there were also changes to data layouts in RTs, addition of wear data as it became available and the simplified met data using Taylor tables.

[jwduquette1]

The reason why I think chg S is a better comparison is that its MV and max range are closer to 88mm.  As I said in my first post on this I think 88mm max rg s2s was 14+ km.  The point is that dispersion tends to increase as max range is approached, therefore if you compare at a range that is max rg for one gun and 80% max for another you don't get comparable figures.  The 25 pr chg S figures are clear, at 1 km its 30 vs 69, at 10 km  80 vs 75.  Howver in actually the 25 pr figures could be anywhere between 26 & 34 or 76 & 84.

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Hi Nigel:

 

Not sure what your point is here. Supercharge and Charge-3 Dispersion Zones are identical -- aside from the point where supercharge continues on in range beyond charge-3 max range. At least according to the Range Table data. One might be inclined to make some more hay here as the projectile descent angles are different for same range shoots. Moreover the slower charge-3 projectile will be crossing the level line or striking the target at steeper angles than the supercharged projectile for the same range setting. Normally we don't see completely identical PEs or 50% Zones between varying charges. But this may be one more reason to question the accuracy of UK range tables of this period. Of course this may all come out in the "figures were rounded" wash

 

If we could return to the reason for this extreme digression for a second. You originally indicated the 88mm spgr dispersion zones looked suspicious. Just to clarify, this is the scientific forum -- or at least that's part of the title. My question to you remains; What scientific evidence do you have to support your suspicions about the 88mm spgr dispersion zones? Or am I being unreasonable in asking for scientific evidence on the scientific forum?

 

Idle speculation is fine and is sometimes interesting, but lets be clear about it. Your speculation is unsubstantiated by anything you have thus far posted. You may be right -- but where's the beef -- where are the numbers? Why would I be inclined to take any stock in your speculation, and discount the firing table data for 88mm spgr.? My natural inclination is to run with the firing table data until some new data set is presented that would make me question the original data set. From the flick Jerry Maguire and Jerry's only client -- "Show me the data".

 

Thus far my own conclusions are that there's nothing wrong with the 88mm spgr dispersion zones. The trends in the 88mm spgr dispersion data look very comparable to inherent dispersion exhibited by other forms of high explosive projectiles. Therefore my estimate for an 88mm spgr projectile striking the coastal artillery target sled as described by Bojan, and based solely upon inherent shot dispersion, remains at 35.5% Perhaps if you were to present some sort of scientific evidence that confirms that there is something wrong with the 88mm dispersion data, than I might redo my original calculations.

 

There are several reasons for the changes to 25 pr RTs, the first edn was for the Mk 1 carriage, which had some limitations.  Then they introduced new varieties of ammo, and there were probably changes in fze wts as 117 evolved.  Also need to compare the driving band patterns, although by WW2 these were fairly stable.  Then there's the propellant varieties, as 175 mm shows (if you believe the FT) this can have some odd effects, although its difficult to pin down a cause and theoretically probably shouldn't happen.  Of course there were also changes to data layouts in RTs, addition of wear data as it became available and the simplified met data using Taylor tables.

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Just so I am clear on your above point, you are now saying that the dispersion figures I posted from the 1939 Range Tables for 25-pdr HE Streamline are correct? You had originally said the figures I posted were “not entirely correct” because the tables were amended within later publications of 25-pdr Range Tables. Ok -- the tables were amended, but the figures I originally posted are as reported in the 1939 Tables. Your modified contention seems to be that various carriage, fuze, ammunition and propellant changes were resulting in the contrasts in the dispersion zones between the 1939 Range Tables and 1943 amended Range Tables? Sort of odd that the gun and ammunition changes invoked between 1939 & 1943 actually resulted in the 1943 gun being considerably less accurate than the 1939 gun. A drop from a higher branch on the evolutionary tree back down to a lower branch. But perhaps this can be chalked up to a steady reduction in quality of equipment and ammunition as the war progressed (idle speculation on my part). In essence you seem to have said that the 1939 tables are correct, and the 1943 tables are correct. Is that about the size of it?

 

Regards

JD

Edited July 8, 2006 by jwduquette1

[nigelfe]

First 25 pr Chg 3 and chg S PEs are nowhere near identical. The only identical points are at 1000, 2000 and 10000. Note I'm using real metres not an old RT and calling yards as metres for comparison with 88mm. I'm using data from the 1967 RT, which still rounds 50% zone data to the nearest 10 m, or more likely the underlying PE to 5 metres. I'd assume that in producing this RT the old data was reworked not just to reflect mils, metres, etc, but also the ICAO standard atmosphere replacing the 1942 WO Std Atmos (whose adoption may have been another reason for one of the wartime RT revisions). What I don't know is whether this rework was a complete rework of the original R&A firing data by computer, re-scaling the old graphs (these used graph paper measured in feet) or something else. Since by 1967 25 pr was only used by a few training units I'd guess the cheapest and 'close enough is good enough' prevailed.

 

The unusual feature of 88mm is the extremely small change in PE over the first 10km of range, we can't actually tell what 25pr is really like due to rounding. But for most guns there is a noticeable curve throughout its range at any charge, an increasing rate of change as max rg is approached characterises some guns. For a comparison with 88mm try M109A1 ch 6W, this has max rg 12100 and ToF within a second of 25 pr. At 1000m 50% is 18m, at 6000 its 36 and by 12000 its 64. Or FH70, chg 5, max rg 12400, ToF 2 secs less, PE at 1000 2 m, at 6km 22m at 12km 44m.

 

As I previously said the only other oddball I can find that looks anything close to 88mm is 175mm chg 1 G.

 

Of course there's another issue to be considered when comparing RTs, and that is the national policy on gun wear. Some nations built their FTs on new gun, ie unworn. Others, used the peak MV (remember MVs actually rise in the early life of a gun), others, incl UK used an MV well after peak and into the first quarter of life. Of course this mainly affects the correction for non-std MV but it's also possible that it was reflected in PE data, which would explain the rounding - of an estimate, with updating when actual data became available. I know the publication that might reveal the policy but won't be near a copy for a while.

[jwduquette1]

FROM Nigel:

First 25 pr Chg 3 and chg S PEs are nowhere near identical.  I'm using data from the 1967 RT, which still rounds 50% zone data to the nearest 10 m, or more likely the underlying PE to 5 metres.

 

Hi Nigel:

 

They are indeed identical in the 1943 25-pdr range tables. Exact! Range breaks at which increases in the length of the 50% zone match perfectly -- as per the data printed in the tables of interest. I have repeated the RT data precisely in my previous posts. The longer range of the supercharge is the only change. You would of course need to get yourself a set of these tables so that you know what it is you are talking about. Frankly, I find it amazing that you do not have these tables. You profess to be an expert on UK artillery from WWII. Yet you have never examined the range tables for the 25-pdr of this period??? Surely you are not posting information on your web site with respect to the 1967 RTs and claiming it to be circa-WWII data? For shame.

 

The War Office – or who ever is in charge of such SNAFU’s – changed the tables yet again in 1967! Are you sure there wasn’t another series of changes in the gun, or propellants, or fuzes between 1943 and 1967. Maybe they added a muzzle break? Or are you implying that it took the UK almost thirty years to figure out the ballistics of the 25-pdr. You sure they got it right in 1967?

 

FROM Nigel:

I'm using data from the 1967 RT, which still rounds 50% zone data to the nearest 10 m, or more likely the underlying PE to 5 metres.  I'd assume that in producing this RT the old data was reworked not just to reflect mils, metres, etc, but also the ICAO standard atmosphere replacing the 1942 WO Std Atmos (whose adoption may have been another reason for one of the wartime RT revisions).  What I don't know is whether this rework was a complete rework of the original R&A firing data by computer, re-scaling the old graphs (these used graph paper measured in feet) or something else.   Since by 1967 25 pr was only used by a few training units I'd guess the cheapest and 'close enough is good enough' prevailed.

 

Any "Firing Tables" worth their salt will have the Standard Conditions indicated at the begining of the tables. You should know that. However this doesn’t invalidate previous sets of range table data in and of itself. All this does is change the standard conditions at which the tables are "calibrated". All "firing Tables" worth their salt will include adjustments for non-standard conditions. Surely you understand this? By the way the UK standard conditions do not change between the 1939 RTs for the 25-pdr and the 1943 RTs for the 25-pdr. One more reason to think you have never actaully seen the WWII tables.

 

In your previous posting you attributed changes between the 1939, 42 and 43 Range Tables for 25-pdr HE Streamline to a new carriage and new propellants and fuze changes (by the way, the fuze designations are the same for the 39 thru 42 tables -- No.117 & No.119). Now your tossing in changes in standard conditions -- but this latter bit, like the fuzes bit, is false and suggests a fair bit of confusion on your part regarding the progression of such changes and when they were actually implemented. Standard conditions used for the tables between 39 to 42 were the same. Identical. You were implying that such changes are at the heart of the numerous reissues of the 25-pdr range tables. This, as you should know, doesn’t invalidate the data within the previous set of tables. Moreover the data from the previous tables was accurate for a set of specific conditions, specific equipment and specific ammunition for which they were developed. Of course the alternative is that these guys didn’t know what they were doing. So they had to keep changing the RTs. I am gueeing that are implying either:

 

1) There was nothing wrong with the 1939 Tables or 1942 Tables or 1943 Tables as they were developed for a different carriage – or different propellant – or different fuzes – or different standard conditions. Therefore each set of tables is accurate for conditions\ammunition\equipment for which they were specifically developed.

 

2) The UK didn’t understand exterior ballistics during this period and were continuously having to re-issue their range tables each time new empirical data became available or after complaints from soldiers trying to employ the tables was analyzed.

 

FROM Nigel:

The unusual feature of 88mm is the extremely small change in PE over the first 10km of range, we can't actually tell what 25pr is really like due to rounding.  But for most guns there is a noticeable curve throughout its range at any charge, an increasing rate of change as max rg is approached characterises some guns.  For a comparison with 88mm try M109A1 ch 6W, this has max rg 12100 and ToF within a second of 25 pr. At 1000m 50% is 18m, at 6000 its 36 and by 12000 its 64.  Or FH70, chg 5, max rg 12400, ToF 2 secs less, PE at 1000 2 m, at 6km 22m at 12km 44m.

 

The plot of the 88mm spgr dispersion zones is also a curve -- even for lower ranged shoots. It shows a low rate of change before transiting to a high rate of change -- like other projectiles -- to include 25-pdr HE Streamline. But the rate of change is continuously changing.

 

You still haven’t produced any evidence to show the 88mm curve is in any way unusual. The fact you don't like the rate of change is meaningless. All we have is your gut feel. But this is the scientific forum. Perhaps you can produce some scientific data that validates your supposition? Or should we start calling this the voodoo science forum -- just kidding?

 

FROM Nigel:

As I previously said the only other oddball I can find that looks anything close to 88mm is 175mm chg 1 G.

 

Than it would seem safe to assume that the 88mm spgr dispersion rate of change is not unique or unusual. It resembles the 25-pdr Zones (resembling the data as it was exactly stated in the 1939 and 1943 Range Tables). It has a low rate of change in the dispersion zones at short ranges – transitioning into a steeper curve at long ranges. You have just provided a third example of a projectile with similar trends in its rate of change for its dispersion zones – 175mm chg 1 G. What more is there to disscuss?

 

Best Regards

JD

Edited July 9, 2006 by jwduquette1

[nigelfe]

Hi Nigel:

 

They are indeed identical in the 1943 25-pdr range tables.  Exact! Range breaks at which increases in the length of the 50% zone match perfectly -- as per the data printed in the tables of interest.  I have repeated the RT data precisely in my previous posts.  The longer range of the supercharge is the only change.  You would of course need to get yourself a set of these tables so that you know what it is you are talking about.  Frankly, I find it amazing that you do not have these tables.  You profess to be an expert on UK artillery from WWII.  Yet you have never examined the range tables for the 25-pdr of this period???  Surely you are not posting information on your web site with respect to the 1967 RTs and claiming it to be circa-WWII data?  For shame.

 

The War Office – or who ever is in charge of such SNAFU’s – changed the tables yet again in 1967!  Are you sure there wasn’t another series of changes in the gun, or propellants, or fuzes between 1943 and 1967.  Maybe they added a muzzle break?  Or are you implying that it took the UK almost thirty years to figure out the ballistics of the 25-pdr.  You sure they got it right in 1967?

Any "Firing Tables" worth their salt will have the Standard Conditions indicated at the begining of the tables.  You should know that. However this doesn’t invalidate previous sets of range table data in and of itself.  All this does is change the standard conditions at which the tables are "calibrated".  All "firing Tables" worth their salt will include adjustments for non-standard conditions.  Surely you understand this?  By the way the UK standard conditions do not change between the 1939 RTs for the 25-pdr and the 1943 RTs for the 25-pdr. One more reason to think you have never actaully seen the WWII tables.

 

In your previous posting you attributed changes between the 1939, 42 and 43 Range Tables for 25-pdr HE Streamline to a new carriage and new propellants and fuze changes (by the way, the fuze designations are the same for the 39 thru 42 tables -- No.117 & No.119).  Now your tossing in changes in standard conditions -- but  this latter bit, like the fuzes bit, is false and suggests a fair bit of confusion on your part regarding the progression of such changes and when they were actually implemented.  Standard conditions used for the tables between 39 to 42 were the same.  Identical.  You were implying that such changes are at the heart of the numerous reissues of the 25-pdr range tables.  This, as you should know,  doesn’t invalidate the data within the previous set of tables.  Moreover the data from the previous tables was accurate for a set of specific conditions, specific equipment and specific ammunition for which they were developed.  Of course the alternative is that these guys didn’t know what they were doing.  So they had to keep changing the RTs.  I am gueeing that are implying either:

 

1) There was nothing wrong with the 1939 Tables or 1942 Tables or 1943 Tables as they were developed for a different carriage – or different propellant – or different fuzes – or different standard conditions.  Therefore each set of tables is accurate for conditions\ammunition\equipment for which they were specifically developed.

 

2) The UK didn’t understand exterior ballistics during this period and were continuously having to re-issue their range tables each time new empirical data became available or after complaints from soldiers trying to employ the tables was analyzed.

The plot of the 88mm spgr dispersion zones is also a curve -- even for lower ranged shoots.  It shows a low rate of change before transiting to a high rate of change -- like other projectiles -- to include 25-pdr HE Streamline.  But the rate of change is continuously changing. 

 

You still haven’t produced any evidence to show the 88mm curve is in any way unusual.  The fact you don't like the rate of change is meaningless.  All we have is your gut feel.  But this is the scientific forum.  Perhaps you can produce some scientific data that validates your supposition?  Or should we start calling this the voodoo science forum -- just kidding? 

Than it would seem safe to assume that the 88mm spgr dispersion rate of change is not unique or unusual. It resembles the 25-pdr Zones (resembling the data as it was exactly stated in the 1939 and 1943 Range Tables).  It has a low rate of change in the dispersion zones at short ranges – transitioning into a steeper curve at long ranges.  You have just provided a third example of a projectile with similar trends in its rate of change for its dispersion zones – 175mm chg 1 G. What more is there to disscuss?

 

Best Regards

JD

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'Unique' - perhaps not, 'Unusual' - most certainly.

 

With a bit of imagination any curve can be said to 'resemble' any other curve. However, the data is what we're concerned with, not pictures.

 

The facts as I understand them are that between 1000 - 10000m (not yards) 88mm 50% went from something like 67 to 75m, a change of around 10%, after 10000m it grew quite rapidly, which is not unusual. It's the prolonged, to some 2/3 of max range, extent with a very small increase that is highly unusual.

 

Apart from 175mm chg 1G I can't find anything else that exhibits anything remotely like this pattern. And 175mm was recognised by some who had a fair amount to do with it as being a bit unusual in its MV behaviour.

 

Consistency is mainly a function of round to round variation in MV. At least as documented in RT/FT, there are other inconsistencies such as laying and ramming which can have a significant effect on fall of shot consistency but the tables don't reflect these (I think). However, it does raise an interesting question about national 'rules' for calculating 50% (or PE) and whether valid international comparisons could be made, I'd hazard a guess that the NATO STANAG on TFTs standardised the method. But in WW2 it could well be comparing chalk and cheese.

 

UK RTs seem to get the shells into the right place, although FAWG of SCARF did identify several of areas for improvement. You can get a handle on these from the Errors & Mistakes page on my site. In WW2 all UK RTs that I've seen round 50% to 10 yds. It was quite a reasonble thing to do since this data wasn't used in any gunnery calcs. What I don't know is the basis for rounding, was it up, down or normal arithmetic rules. Since the significance of 50% was troop safety its possible to believe that it was up, although I think it was more likely to be the conventional approach.

 

UK issued amendments to all their RTs and in 25pr case several revisions. There's a pile of possible reasons for these - new ammo, the introduction of intermediate chgs and upper register fire, taylor tables, new propellant (eg AN), new fuzes. Both fze wt and driving band pattern can also affect ballistics (at least the Brits believed so - see AT Vol 3 Provisional 1921, not to mention later publications). The 1967 change was different as any moderately well informed schoolboy knows (I think the younger person's expression is 'duh') - NATO standardised its units of measurement to mils, metres, etc, UK had to change a lot, then there was the change to ICAO 10 yrs earlier although in that case 25 pr RTs were merely amended (and don't forget the impact of the ballistic met msg STANAG as well).

 

And they did change their standard atmosphere in 1941 and soon after issued a new edition of MO317 to replace the 1929 edn (this instructed the RAF how to prepare arty met msgs). However, looking at the data I doubt if it affected 25 pr.

 

Given UK 50% rounding it's very dodgy to compare UK rg & 50% in yards with GE rg & 50% in metres. However, the benefit of the 1967 RT is that it is in metres and so is directly comparable to 88mm. The pattern is the thing, and to keep the comparison with 88mm, the best is chg S, but instead of 10000 m use 8000, ie 2/3 max range which is what 10000 is for 88mm. 25 pr goes from 30m to 70m, ie a change of over 100%, not 10% exhibited by 88mm. Applying the same to chg 3 then 1000 is still 30m and 7000 is 50, still an increase of 66% not 10%. However, 25 pr also doesn't increase as rapidly as 88mm beyond 2/3 max rg to max rg, 70 to 90 at Super, 50 to 80 at chg 3. If you want to use 10000 then obviously the 25 % increase is even greater.

 

As I said a while back, I actually think a more appropriate comparison with 88 would be 3.7 HAA because the guns were designed for the same role, although 3.7 in the ground role delivered shells somewhat further than 88mm. The only reason I can see for using 25 pr is that the calibre is very close to 88mm, but MV is much lower as, I think, is calibre length of the barrel, which may also influence the MV variation.

[jwduquette1]

Hi Nigel:

 

Things are going like gang busters here at the gulag, so I will have to content myself with but a few comments regarding your latest.

 

 

With a bit of imagination any curve can be said to 'resemble' any other curve.  However, the data is what we're concerned with, not pictures.

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On a recent thread you said something to the effect of:

 

“Until forced to use TFTs by NATO the Brits used a graph in RTs for non rig which is quicker than lookup and multiplication. However, Ft Sill seems to have had an aversion to graphs in FTs.”

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See Page-3 of the following thread: http://63.99.108.76/forums/index.php?act=Forward&f=8&t=16068

 

I realize graphical representation of data can be a complex concept for some, but after your above remarks, I had assumed that you might require pictures. Ala those complimentry angle figures in UK RTs that you are apparently so fond of. Sorry if my rather simple figures are a source of confusion for you. I regret to tell you this, but this is very common way of conveying and sharing large amounts data. It is also a very useful means by which trends in data can be determined. For example the similar trends in the rate of change in the dispersion zone lengths for 88mm spgr and 25-pdr HE Streamline become fairly obvious after examining the plotted data. I think if you had looked at trends in dispersion data in this manner before leaping into this, I wouldn’t have to be wasting my time generating these plots. But you are of course always welcome to ignore all relevant information to this particular sub-topic.

 

As to the rest -- sorry, but you started meandering -- I assume what you are attempting to say is that the 25-pdr RTs issued in 1939, 1942, and 1943 are correct for the specific conditions under which the tables were prepared. Is this a fair take regarding your opinion on this particular bit? For the sake of brevity perhaps you would be kind enough to oblige me with a simple yes or no. Thanks a bunch.

 

Best Regards

JD

Edited July 10, 2006 by jwduquette1

[nigelfe]

Managed to spend a few minutes today comparing 1939 and 1953 25 pr RTs, but only time to compare chgs Super & 3 and only looked at the main data table so I could well have missed a gem or two.

 

First point is that 1939 are missing key data, no correction for variation in chg temp. I assume this was issued as an early amendment. Also 1939 didn't provide chg S data below 10500, whereas 1953 started at 100.

 

50% data very different at both chgs. In addition at Super Air Temp correction differs slightly from 11500 up.

 

Chg 3 data has a lot of differences, including A of P, T of F, Bar and Air Temp, although apart from 50% the differences are small. The 1953 data shows 30 yds at 3000 and then, roughly, adds 10 yds every 1500.

 

From this I think we can assume that the 1939 RT was not overly accurate! Its possible that the Chg 3 data reflects different propellant. Unfortunately there isn't anything saying what props were used for R&A firings, and I couldn't find any R&A firing dates (which would indicate whether there was new data or reworked data), but didn't have time for a full search. 1953 has a lot more Notes.

 

There's other interesting points, for example the 1953 edn it gives different new gun MVs for Mk 2 and Mk 3 guns, I think this may reflect slight differences in breech machining that would fractionally affect chamber volume.

 

However, both tables state that 50% are for the 1st qtr of life (but not at what stage) and ideal experimental conditions using propellant from the same lot. 1953 also states that with mixed lots multiply 50% by 1.5 and if the gun is in 2nd qtr by 1.75! 1939 also says double the 50% to obtain a practical one! I actually think these are overly cautious, but you'd expect this for 50% data which in peacetime is mainly used to determine safe impact areas on arty ranges.

 

The point is that 50% data needs to be treated with caution. While it is basically, if not entirely a function of rd to rd variations in MV these can be significatly affected by various conditions of wear, etc.

 

However, given that the main source of range PE is MV then self-evidently the effects on the ground will vary with range, the RTs show this - a change in 10 f/s requires a correction that varies with range, it's not constant. Hence if you establish the PE in MV rd to rd, you have a number that can be directly related to the correction to range for variation in MV. For those that like pictures, I think this means that a graph of the correction for MV variation should exhibit a curve that 'very closely resembles' that of 50% in shape. I confess I've never tried this (I'd do it with a modern high quality FT), any differences would have other causes but we now get into the thorny area of 'unattributable variations' in MV or what the modern experts call 'white' and 'coloured' noise, and such things as occasion to occasion effects, gun to gun effects, cold gun effects, etc.

 

Now this is where it gets really interesting. The Brits tried from 1916 onwards to connect MV determined instrumentally with MV determined by fall of shot calibration. They knew there had to be a relationship, they knew that with a worn gun fos (ie actual range fired) was affected by instability but try as they might they could not find the relationship. Then, lo and behold, in the 1950s they started using doppler radars, suddenly the 'instrumental' data made sense and the relationship with fos revealed.

 

The problem was that earlier instrumental methods were inaccurate but fos was actually pretty good at getting the 'truth'. The point for this discussion is how did the Brits (and Germans and US) measure MV during R&A firings (WW2 era), did they use both methods, did they combine the results or pick one or other? Clearly using the wrong rd to rd MV variations from R&A firings would lead to wrong 50% zones! Voila! (I think, I'm reasoning from first principles here).

 

RTs made use of graphs, and very useful there were too, lots of curves all resembling one another. But if you're really smart they are rather simple to understand.

[jwduquette1]

You’re only now starting to review the range tables? So up to this point your statements regarding the dispersion data I had previously posted being "not quite right" had no basis. I would think an apology from you would be in order.

[jwduquette1]

Another graphical representation of dispersion data for several projectiles. Again, I am simply looking for “unusual” or “unique” trends in 88mm spgr dispersion zone relative to other projectiles. The other projectiles exhibit similar characteristics to the 88mm spgr. dispersion zones. Low rates of change in the initial portions of the curve followed by increasing rates of change over the longer ranged segments of each respective curve.

 

Edited July 12, 2006 by jwduquette1

[nigelfe]

At last, recognition that the 25 pr 1939 50% data is sus, a point I made ages back, haven't tried converting 1953 yds to 1967 metres but I'll put money on them being consistent with each other.

 

90mm and and 155mm G show an entirely reasonable progression by the curves, particularly when you look at the rate of change over range. Not sure about 105mm, I've only got M/L119 firing M1 HE (R&A probably circa 1973) and it looks different, for 50% 16m at 1 km to 58 at 11km, and a very steady pattern of progressive increase - 16, 18, 22, 26, 32, 36, 40, 46, 50, 54, 58, slight blips at 5 & 8km, but otherwise very smoothe.

 

Interesting how 90mm, another HAA, shows how odd 88mm is.

[jwduquette1]

That’s great Nigel. Just for the record, it is pretty clear now that you believe that when it came to the science of exterior ballistics, the UK had absolutely no idea what it was doing. Your postings on this thread continue to prove this point very effectively each and every day.

[nigelfe]

I'm having great difficulty following the reasoning here.

 

The UK basically invented the field gunnery use of applied external ballistics in the 20th century and maintained that lead to this day. For example as far as I am aware they are the only country to have successfully developed MV prediction, even if they haven't deployed it yet, and were, of course, the first nation to stop using any optical indirect fire sight (and possibly still the only one). They developed a particularly efficient, effective and flexible system of gunnery. This system emphasied their gunnery values - rounds on the ground as fast as possible and a willingness to trade pedantic accuracy for greater speed when it was approprate.

 

I make no claims to be a ballistician. But field gunnery is not unknown to me. So keep reading my work and keep learning.

 

One or two people have emailed me to say they have a problem connecting to my web site, probably a legacy of the host re-configuring the URL a while back. This should be OK http://members.tripod.com/~nigelef/index.htm I'm still a few weeks from publishing a history of UK arty technical fire control in the 20th C. It's amazing that no one has ever published such a thing before, even for the first half of the C, so its all based on primary sources.

[starkweatherr]

I have a few questions. I hope they are relevant.

 

My last tank was an M-60A1 RISE/PASSIVE in 1978. I had thought that it was very similar to an M-60A3, but it appears that there were some differences since it still had the old mechanical ballistic computer.

 

Item 1. We never adjusted the knob for gun tube wear. It was always left in the 0-0 position. Many tank commanders in my unit had no idea how many rounds had been through their tubes, or even where the appropriate page in the tank's log book was. Consequently, we NEEDED to do a one time zero every time we went to the range. After boresighting and slipping the scales my first three boresight rounds were always in the upper left quadrant of the target, but I kept track of the corrections we made and they were not the same for any of the three gunnerys that I went through in that tank, and the three sets of corrections did not form a pattern. Aside from tube wear and weather conditions, two other problems might have been that I didn't have the same gunner, or either of the same sights for more than one gunnery.

 

Item 2. The idea of a 'fleet zero' seems wasteful to me. Even with wind, temperature, and tube alignment sensors how can you expect to hit anything without zeroing? Are the sights in Abramses fixed in the sense that they can't be removed at all? Are they an integral part of the turret or are they repairable sub-assemblies? Any time one of our sights had a reticle crash or even a nitrogen refill at the range, we got a check round. If our sights were replaced, as happened fairly often, we re-zeroed. Very expensive, but are you suggesting that is no longer necessary?

 

Item 3. In the unit I was in (we had two Master Gunners in the company, BTW.) The TC was responsible for boresighting and zeroing. The driver was in his compartment, and the gunner operated the manual controls and emergency firing device, but the loader wasn't even aboard. Some people let the gunner use his sights, but I always felt that they were a distraction and had them removed before zeroing. I zeroed the range finder and referred the gunners sights to it after we were off the range. You have to remember that my normal crew was myself and a driver. In two years I never had a gunner assigned so I used whoever was available at the moment. I had to use a turret mechanic for one firing table.

 

Item 4. Long range gunnery in the sense of sniper tanks seems like a real waste of time and money unless thermal sights can see through heat haze and moist air. You're not going to be able to get a good look at a target in Germany at more than 3500 meters except during the winter, and I doubt that there are many occasions in the Middle East, unless you are firing up at a target or across a valley that you will be able to do much better. Too much moisture in the air in Europe, and thermal sights aren't going to make that go away, and too much heat haze in the desert, and I would think that thermal sights would be even worse there.

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Item 2. The idea of a 'fleet zero' seems wasteful to me.

An old article for an old tanker:

New Tank Gun Calibration Policy - Armor july-august 1982

 

For the comparison of different tank gun calibration policies, I posted in this thread with post #21 of 25 June 2006 standard-deviations for the calculation of hit-likelihoods with one round.

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In addition to my previous post:

 

Since 1987 Swiss tankers fire with fleet zero.

 

To convince the tankers of the advantages of the fleet zeroing, a firing was enforced with 24 Swiss Tanks 68 (Pz68) with 105 mm rifled guns. The following picture shows a selected result from this firing.

 

 

The procedure was:

- Boresighting with muzzle boresight device

- Same zeroing correction for all 24 tanks on the basis of the mean value of a single zeroing with 5 tanks (fleet zero)

- Each tank fired one APDS M111 at a range of 1130 meters

- Grid dimension: 200x200cm

 

The accuracy is impressive. Comment isn’t necessary!

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Sorry, the link was wrong

 

[Rick Griest]

That diagram is quite impressive. It is saying that 24 separate tanks achieved essentially 100% impacts of a 0.5 mil pattern at roughly a km. This isn't far off the manufacturer claims for his round to round dispersion for his standard deviation! (0.25 mill for std.dev claimed) Quite remarkable. Was the ammo Israeli made or Swiss?

 

Thanks Arrow.

 

Rick

Edited August 20, 2006 by Rick Griest

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Israeli made or Swiss?

The ammo was a licence product. Sabot and cartridge case were Swiss made. Assembly of the components was worked out in Switzerland.

[Ssnake]

That diagram is quite impressive.  It is saying that 24 separate tanks achieved essentially 100% impacts of a 0.5 mil pattern at roughly a km.  This isn't far off  the manufacturer claims for his round to round dispersion for his standard deviation! (0.25 mill for std.dev claimed)  Quite remarkable.

Are we talking about the same image?

Nine out of 24 are outside the .25mil radius around the zero coordinate, that's 62.5%, not 100...?

[jwduquette1]

I'd estimate the 50% Zone to be about 0.548-mils. -- give or take. About 50% of the hits are within about +/- 0.31meters of the aiming point -- assuming the aim point is the center of the 2m x 2m Box.

Edited August 21, 2006 by jwduquette1

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Are we talking about the same image?

Nine out of 24 are outside the .25mil radius around the zero coordinate, that's 62.5%, not 100...?

359777[/snapback]

Hello Ssnake

 

Rick’s evaluation refers on the mean point of impact:

azimuth -20cm

heigth 7cm

 

Standard deviations (referring on MPI) are

azimuth 27cm 0.24mils

height 29cm 0.26mils

 

CEP (radius around the impact coordinates) is

0.292 mils

 

The fleet zero used at the firings was a rough estimation, which has to be tuned to the actual fleet zero. So Rick’s evaluation is o.k.

[Ssnake]

Ah... I see.

[jwduquette1]

Hello Ssnake

 

Rick’s evaluation refers on the mean point of impact:

  azimuth -20cm

  heigth 7cm

 

Standard deviations (referring on MPI) are

  azimuth 27cm 0.24mils

  height 29cm 0.26mils

 

CEP (radius around the impact coordinates) is

  0.292 mils

 

The fleet zero used at the firings was a rough estimation, which has to be tuned to the actual fleet zero. So Rick’s evaluation is o.k.

359849[/snapback]

 

Very interesting as usual. Thanks Willi.

 

I did my calcs based upon what I assumed was the aiming point – dead center of the 2m x 2m box. The Blue Circle is my 50% Zone. The Yellow Circle is your CEP around the true MPI.

 

FIGURE: Swiss Fleet Zero Trials, M-111

 

The end result for my dispersion zone calcs are relatively close to your own numbers. Unfortunately, I don’t have the X and Y coordinates of the hit locations, so I had to do a bit of schlocking in my calculations. But yes, I should have determined the true MPI and than backed out the CEP.

 

If the MPI of 24-tanks is skewed slightly to the right and up from where I assume the aiming point is located (assumed to be dead center of the 2m x 2m box), wouldn’t it make sense to ratchet the fleet zero for M-111 back slightly to the left and slightly down? Obviously more than one shot per tank would be required to nail down the true MPI from the fleet zero. But assuming these 24 shots were fairly representative of a much larger sample. The MPI being skewed away from the aim point should decrease the overall fleet hit probability. Perhaps nothing of significance at 1130m, but what of the effect at say 3000m or 4000m? Long range.

 

Best regards

Jeff

Edited August 22, 2006 by jwduquette1

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If the MPI of 24-tanks is skewed slightly to the right and up from where I assume the aiming point is located (assumed to be dead center of the 2m x 2m box), wouldn’t it make sense to ratchet the fleet zero for M-111 back slightly to the left and slightly down?

Yes, see my statement in post #97:

The fleet zero used at the firings was a rough estimation, which has to be tuned to the actual fleet zero.

 

Obviously more than one shot per tank would be required to nail down the true MPI from the fleet zero.  But assuming these 24 shots were fairly representative of a much larger sample.  The MPI being skewed away from the aim point should decrease the overall fleet hit probability.

For the comparison of different tank gun calibration policies, I posted in this thread with post #21 of 25 June 2006 a statistic model and the standard-deviations for the calculation of hit-likelihoods with one round, under the assumption that MPI is identical to the aiming point.

 

For fleet zero of modern tanks and APDSFS these standard deviation for a single round (sr) is:

 

s_sr = sqrt(s1^2+s2^2+s3^2)

std dev in height = sqrt(0.10^2+0.15^2+0.20^2) = 0.27 mils

std dev in azimuth = sqrt(0.05^2+0.10^2+0.20^2) = 0.23 mils

 

Good correspondence with the Swiss trial (0.26 resp 0.24mils)!

 

The standard deviation of the investigated fleet zero correction – i.e. with the 24 Swiss tanks and one round per tank – can be estimated with the following formula (individual for height and azimuth):

 

s_fz = sqrt(s1^2/n1 + s2^2/n1/n2 + s3^2/n1/n2/n3)

 

n1 = number of involved tanks

n2 = number of firings per tank

n3 = number of rounds per tank and firing

 

Swiss trial:

 

n1 = 24 / n2 = 1 /n3 = 1

 

height: s_fz = 0.055

 

azimuth: s_fz = 0.047

 

You see, with only 24 tanks and one round per tank we got a very good estimation for the fleet zero correction.

 

Regards