Main Gun Ammo - Revisited

[Junior FO]

Swiss Pfeil Pat (IMI M111, M30 powder) tests from 1983

Monoblock penetration (S, in mm) approx linear formel valid  for v(impact) 1275m/s < 1425 m/s

S = 0.73 x v(impact) -660

 

penetration tests

152mm monoblock plate (895 N/mm2)

@60° @1322 m/s penetrates 304mm
@64° @1381 m/s penetrates 347mm

Vo reduction from barrel burn

calibre increase per round = 0.002 mm

0.1mm calibre increase results in Vo reduction of 2.6 m/s

 

Adjustment of existing APDS scales if gun is zeroed with Pfeil Pat @1500m

0-2000m none

2000-2700m -100m

2700m-3000m -150m

with the above adjustments the difference of the aimpoint is less than 1/8 %o throughout

No mixing of APDS/APDSFS, gun needs to be rezeroed with APDS for APDS use.

 

QC for Pfeil Pat acceptance (barrel in 1st quarter, calibre equal or less than 105.5mm)

Vo 1448 +/- 15 m/s @15 C°, 50% V spread not more than 8 m/s

measured at 1m from muzzle (=0.04 m/s)

correction for calibre above 105.00mm: 0.1mm = 2 m/s

height and side dispersion less or equal 0.4 %o (0.4m @ 1000m)

charge mass difference of 8-50g small fault, larger than 50g significant fault

penetrator mass out of tolerance is not a critical fault, can be re checked

 

Swiss Normal conditions for tank ammunition

Powder temp 15C°

Air temp 6C°

Air pressure 922 mbar-> approx 800m over sea

Air density 1.15kg/m3 -> ""

 

Swiss tank munitions plan in 1982

50k M111 rounds with RP 81

30k (the M413 from above) in 84/85 (removal of L28 and L52A2 from war stock)

80k 2nd. Generation rounds 87/88 (removal of L52A3 from war stock)

70k HEAT from 1989 and phasing out of HESH

Edited September 23, 2023 by Junior FO

[sunday]

Was there any purchasing program for turrets taken off of tanks and put in fixed positions?

[Junior FO]

1 hour ago, sunday said:

Was there any purchasing program for turrets taken off of tanks and put in fixed positions?

Considering that was in the 90's and coincided with the massive reduction in the 105mm tank fleet, I doubt it.

[Junior FO]

https://ufile.io/k5d9eqwm

Page 9

Pz Kan 61

Charge mass, projectile mass, powder temperature, Vo,  Muzzle Energy, (in % of L52), Muzzle Impulse, (in % of L52), Recoil Energy, Brake Power, average max gas pressure 

detailed explanation for the above values on page 2 section 2:

The muzzle data includes 50% of the powder mass, the recoil energy values are rough estimates and to be seen as indicative only. In the brake power column test data on average and max brake power values are added where available. Gas pressure is from local aggregated tests. Due to the intention to later aquire a HEAT round, the US M456A1 is included.

 

L28

L52

M111 (PfeilPat)

HESH

M456A1

 

the other entries are pratice rounds, inert rounds etc.

 

It seems the Pz Kan 61/68 recoil system was having problems with high energy rounds, needing to be checked/serviced after every 100 rounds of APDS/APDSFS. This was fixed with a revised recoil system in the mid 80's.

 

 

[Wiedzmin]

36 minutes ago, Junior FO said:

It seems the Pz Kan 61/68 recoil system was having problems with high energy rounds, needing to be checked/serviced after every 100 rounds of APDS/APDSFS. This was fixed with a revised recoil system in the mid 80's.

is there similar data for L7?

[Junior FO]

23 minutes ago, Wiedzmin said:

is there similar data for L7?

No, but SOP varied considerably from Nation to Nation and probably can't be compared regardless of technical details.

F.e. with additives in the early 80's the APDS L28/L52 barrel burn was reduced so far as to increase barrel life from 200 to 2000 (UK Mod information) rounds, however due to fatigue considerations Switzerland drew the line at 1000 rounds with existing barrels.

Another case is Israel, they fired proofing rounds for powder and case lots from normal guns with old barrels from T55's, even though pressure dispersion means there must have been spikes well above the theoretical maximum.

[Wiedzmin]

29 minutes ago, Junior FO said:

barrels from T55's,

you mean T-55 with D-10T swaped barrels toL7 or which?

 

Israeli IIRC also had a lot of problems with M392 and L28/36 APDS during wartime use ?

 

btw sidenote 

 

swiss Centurions used their own reticle(german style), not british 

 

 

Edited September 23, 2023 by Wiedzmin

[sunday]

2 hours ago, Junior FO said:

Considering that was in the 90's and coincided with the massive reduction in the 105mm tank fleet, I doubt it.

Thanks!

I see Switzerland did not use the 20pdr gun on Centurions.

[Junior FO]

18 hours ago, Wiedzmin said:

you mean T-55 with D-10T swaped barrels toL7 or which?

Apparently entire installed L7, though I don't know whether this is assumption of observer or if he went inside to check if it was not only a barrel swap.

 

18 hours ago, Wiedzmin said:

Israeli IIRC also had a lot of problems with M392 and L28/36 APDS during wartime use ?

Don't know, but in Swiss service as detailed above the L28 center bands and primers were an issue. It seems the L3A1 primers became very sensitive when corroded and there were cases of primers igniting from the static charge of hands when they did the refurbishment programm.

18 hours ago, sunday said:

Thanks!

I see Switzerland did not use the 20pdr gun on Centurions.

All 300 were bought as 20pdr tanks. 150 were upgraded early 60's, the rest late 70's.

[Junior FO]

On 9/11/2023 at 3:05 PM, Junior FO said:

Swiss trials and tribulations with UK APDS ammunition

UK lot numbers like 46-63 I assume means from 1963

 

L52

In the early 80's Switzerland must have started to use L52 in training (next to L28A1), even though the A3 lots were only delivered from 1978 (20% of total) to 1981 (the other 80%).

Hangfires and being unable to load rounds due to the center band rapidly swelling from humidity led to further investigations.

In 1984 Switzerland informed the UK that it there were problems. The UK MOD had apparently been aware of himidity issues with for a long time since it changed the packaging already in 1979 (without informing Switzerland there might be a problem) and initially it maintained the issue did not affect rounds packaged 1979 to 1981 and was only willing to treat the pre 79 lots as a guarantee case.

Switzerland took a 960 round sample from its 16 production lots and found that only 30% of the centerbands were in spec. UK MOD initially was going to offer a machine solution, however this proved unworkable in the time frame, as MOD increased tolerances, changed the measuring method and wanted 3 different specs for trimming the bands based on the existing amount of swelling. This meant the work could only be done manually.

Primers

Subsequently Royal Ordinance allowed Switzerland to also test the L1A4 primers (I'm surprised this needed to be authorised). Primer lots from 1971, taken from various munition lots 1963 to 1973 were tested, all failed spec and the dismantled ones showed signs of corrosion (strongly in somewhat less than half the cases). In multiple cases measured primer delay exceeded a second.

In the refurbishment programm that followed from this I see half the L28A1 (1963 lots) were given IMI primers, and all but one lot of the L52A2's (1971 lots). Don't know if the list is complete.

Contamination

The L52A3 subsequently seems to have been fine, for 1986 a sample of 6364 rounds was released of which 5541 were expended without issue, the rest to follow in 1987.

However the story does not end for L52A2. Two lots of refurbed ammo from 1985 were released in 1986 as well but had to be pulled due to rounds falling short. Investigations showed that this was due to the rotation of the rifling not being transferred to the core. Disassembly of some rounds from a lot showed contamination in the "transfer mechanism". 200 rounds from the two lots were to be disassembled and examined but I don't have the results.

 

PART II
Unlike how I wrote it above, the centerband issues surfaced after the primer problems, and as late as August 1983 the reconditioning plan only included the additive and a primer replacement.

Starting point of the story seems to have been the decision in 1981 that with the phasing in of the M111 Pfeil Pat, the L28/L52A2 stock would be released for training use in 1985.

The new powder additives drastically increased the barrel life of hitherto only 200 APDS rounds (HESH, HE, Smoke barrel burn was negligble), so it was known that a programm to add the additive would be worthwhile prior to its general release to training. However, due to a premature reduction in the number of bought training APDS, this needed to be brought forward to mid 1983 and it was decided that barrels would be allowed up to 50 APDS rounds of original L28/L52 for training use.

The centerband issues are first mentioned in Oktober 1983 based on reports from a school.

This led to the subsequent centering band checks of the entire stock. The centering bands were also not a new problem, as there had already been a reconditioning effort in 1974-75 for the L28/L52A2 to trim them down to spec.

 

It seems that it was the shooting trials held in preparation for the additive programm where the primer issues surfaced. In March 1982 the Branch testing group (not normal troops) fired 194 rounds from Lot 39-71 (L52A2), of which 16 failed to fire. This led to the provisionary stop order for other L52A2 lots 40-71 and 41-71, based of sample tests.

It's noted that there were no widespread reports of previous cases of failures to fire with L28/L52 but it doesn't mention how often these took place and it's mentioned that the forms for reporting such were unclear and did not specify the lots. Initially it was thought the problems did not extend past the above 3 lots. 

However, further problems must have surfaced because in February 1983 it was decided that all L28/L52A2 lots were to be tested for primer condition and as part of the reconditioning, preparations would be made to also exchange all the primers so provisionally 5000 L4A1 primers were ordered from the UK.

In May 1983 10 L3A1 (from L28) were tested by MOD to the then MOD standard with a current of 100 MicroJoule during which 7 ignited (they should not). MOD couldn't answer if this test had also been done with the Swiss primer lots so it's unclear whether the high L3A1 sensitivity was due to age or had existed from the time of manufacture, but now even cases of the static electricity from a hand setting it off were reported and new safety directives issued.

Despite a decision to use IMI L4A1 primers in the reconditioning programm, in October 1983 a further 6000 L4A1 primers were ordered from MOD due to delays with test firings to certify the IMI version.

 

With the additives exceeding the allowed chamber pressure when >35C°, the decision was made to download the charge by 100-150g depending on lot. The Vo reduction changed the impact point by 0.2%o at 2500m, falling to 0.08%o if zeroed with the downloaded ammunition.

Overall 50% dispersion values only changed by 0.01%o even at extreme temperatures and with shot out barrels at 1668m.

Edited September 25, 2023 by Junior FO

[Wiedzmin]

11 hours ago, Junior FO said:

L3A1 sensitivity

Hm, maybe this was obe of the reason why brits used primer protective caps on their ammo?

[Interlinked]

What was the allowed chamber pressure @Junior FO?

[Junior FO]

On 9/26/2023 at 6:48 AM, Wiedzmin said:

Hm, maybe this was obe of the reason why brits used primer protective caps on their ammo?

Seems likely. The handling guidelines issued with 1983 bulletin for L3A1/L4A1 ammo allowed the primer cap to only be removed once the round enters the ammo rack and all handling of the rounds inside the tank are only to be done wearing loader gloves.

This applied to the 105mm UK APDS/HESH and M111, as well as the 20 pdr UK APDS. However the 53 model 20pdr HE is not listed as having a cap. The only reason I can think of is that the HE still had the pre L3A1 primer.

The non primer cap ammo, aside from the 20pdr HE, Swiss practice rounds, had no such restrictions.

It is noted that the restrictions were UK practice and were known and SOP in earlier years at the armor branch but had fallen out of practice since it had not been part of general ammo handling regulations.

My guess is the above was 20pdr Centurion specific, with the winding down of the 20pdr fleet and no longer using 20pdr war ammo, this fell out of use since not needed with the Swiss 105mm practice ammo.

On 9/26/2023 at 7:29 AM, Interlinked said:

What was the allowed chamber pressure @Junior FO?

I'm sure I saw a number somewhere but didn't mark the file,  IRRC 5000bar., pmax 5190 bar for a cartridge.

 

What  I did mark was the pressure tests with additiv

 

@50C° powder temperature:

full charge    max 5330 bar, S50 dispersion 60 bar

reduced load (-85g) max 4790 bar, S50 dispersion 113 bar

reduced load (-85g) max 4800 bar, S50 dispersion 87 bar

 

measuered with copper crushers, piezo tests were also done but the results of 300 to 1200 bar less was so far below and divergent from the copper crusher ones that they were seen as unreliable and not included.

conclusion:

under consideration of the singular ouliers, an average of 4800 bar is acceptable, the pressure from an unchanged charge mass is definitely too high.

Edited September 27, 2023 by Junior FO

[Wiedzmin]

9 hours ago, Junior FO said:

Seems likely

Btw you sure about 100 MicroJoules? Cause sounds way too little 

[Junior FO]

8 hours ago, Wiedzmin said:

Btw you sure about 100 MicroJoules? Cause sounds way too little 

https://ufile.io/z0ku2qei

page 3 English test set

[Wiedzmin]

omg, thank you 

[Junior FO]

14 hours ago, Wiedzmin said:

Btw you sure about 100 MicroJoules? Cause sounds way too little 

Report on the corroded L4A1 primers, with the destructive test method on pages 9-10.

https://ufile.io/o3nywrkl

The munition monitoring programm for the M111 Pfeil Pat, with the primer test criteria on pages 29-33.

https://ufile.io/6tf4ww79

 

That's all I have.

[Sovngard]

GIAT 1983 vintage video about French APFSDS : basic principles, manufacturing process, testing, beyond-armour effect, packaging. Very interesting.

https://imagesdefense.gouv.fr/fr/munitions-fleches.html

[JWB]

1 hour ago, Sovngard said:

GIAT 1983 vintage video about French APFSDS : basic principles, manufacturing process, testing, beyond-armour effect, packaging. Very interesting.

https://imagesdefense.gouv.fr/fr/munitions-fleches.html

What are the pellets in the front of the projectile?

[Przezdzieblo]

Tungsten pellets for ehanced effect versus lightly armoured targets.
https://patents.google.com/patent/US4353305A

[JWB]

👍

[Junior FO]

On 9/26/2023 at 7:29 AM, Interlinked said:

What was the allowed chamber pressure @Junior FO?

For 105mm L7.

[Interlinked]

Excellent, thank you, this is very very valuable to know.

[Junior FO]

On 9/27/2023 at 8:00 AM, Wiedzmin said:

Btw you sure about 100 MicroJoules? Cause sounds way too little 

 

Don't understand anything about electricity, but it seems that unlike primers that are fired using a bridge wire primer, the L1A3 (and L1A4) have conducting composition cap primers.

If using an Exploding Bridge, the strength of current is important, with a conducting primer compound, the voltage.

 

Test specs from 1977:

L1A3

- @20V must ignite within 0.002 s

- @14V must ignite

-@max 1.5V test voltage 10-250 Ohm without igniting

 

Swiss El Zü Pi 102 (Smoke, HE, Practice-HE)

- @0.5A ignite within 0.025s

-@0.2 A not ignite within 300s

- Resistance 1-2.8 Ohm

 

DM 72A1 (1979)

-@6A ignite with resistance 1-2.5 Ohm

-@0.2A for 18 seconds no ignition

Edited October 19, 2023 by Junior FO

[Junior FO]

On 9/23/2023 at 5:49 PM, Junior FO said:

No, but SOP varied considerably from Nation to Nation and probably can't be compared regardless of technical details.

F.e. with additives in the early 80's the APDS L28/L52 barrel burn was reduced so far as to increase barrel life from 200 to 2000 (UK Mod information) rounds, however due to fatigue considerations Switzerland drew the line at 1000 rounds with existing barrels.

Another case is Israel, they fired proofing rounds for powder and case lots from normal guns with old barrels from T55's, even though pressure dispersion means there must have been spikes well above the theoretical maximum.

It's clear now the 1000 round fatigue limit came from a breech blow in Germany with DM23 in January 1981.

Diehl was conducting -35C° temperature tests with a new primer DM82A1 for the DM23 and was using a barrel with 2800 rounds (of which 1100 increased charge). While the accident was being invesigated a general advisory for a limit of 1000 rounds DM23 was issued by IMI as well as temperature restrictions. In the end the round count was deemed to not have been the cause of the accident but it seems Switzerland kept it.

 

It seems only due to the accident was the interaction between primer - propellant at very low temperatures investigated.

It was found a "soft" ignition was needed to mitigate the shatter effect most powders of the era had, which could lead to pressure spikes. F.e. Swiss tests with DM23 @-32C° resulted in an average of 4401 bar, and a spread of 383 bar while a Wimmis powder with similar corn geometry had led to damaged gun in 1980.

IMI and Germany induced some breech blows by obstructing some of the primer openings, leading to irregular pressure waves. This with both new and reinforced L7's, but the exact cause of the oriniginal accident remained unknown. DM82A1 was deemed the primary cause even though subsequently 400 DM82A1 were fired without issue and it remained unclear if there had been other contributing factors.

Germany was looking for a new primer because DM72 was leading to large Vo spreads while the L1A4 did not fulfill the requirements regarding shock, humidity and ignition latency.

IMI had never before investigated the L1A4 ignition behaviour but it seems this kicked off R&D in this sector.