Official Firefly Testing.

[Manic Moran]

As opposed to the impromptu Isigny tests, I ran across the test report from Fort Knox of the Firefly turret , and am running it over on the WoT site (If you missed it).

http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly/

 

You may find it of interest. Unfortunately, as players tend to have the attention span of a gnat, I'm forced to break it up into a number of parts, but it does beg a question. Presumably the British did their own version of the same thing with the 76mm and 17pr tanks at Longcross or wherever, but I've never seen them. Have I just not been looking hard enough, or is there actually nothing out there? I feel it would make an interesting counterpoint to finish the series.

 

NTM

[Mobius]

I like it.

[shep854]

Informative read. I'm currently going through your "Chieftain's Hatch" articles; they are very enlightening and enjoyable. Thanks.

[Marek Tucan]

Waiting for more The loading tests were neatly demonstrating the issues of tank RoF in combat...

[DKTanker]

I would be interested to see the comparable dispersion results for both 76 mm and 90 mm. At first blush the 17 pdr shows some serious accuracy problems.

[Mobius]

I would be interested to see the comparable dispersion results for both 76 mm and 90 mm. At first blush the 17 pdr shows some serious accuracy problems.

Actually, it is accurate. Too accurate. Since they aren't actually firing at the center of a target the random lay or jump error is elimated. That in many cases has about a s.d. of .12-167 mils.

http://www.dtic.mil/dtic/tr/fulltext/u2/316221.pdf

Edited January 21, 2014 by Mobius

[DKTanker]

Actually, it is accurate. Too accurate. Since they aren't actually firing at the center of a target the random lay or jump error is elimated. That in many cases has about a s.d. of .12-167 mils.

http://www.dtic.mil/dtic/tr/fulltext/u2/316221.pdf

 

I'm not going to go through all of that, just cut and paste that portion which specifically states that a cannon can be too accurate. Or at least provide the page number. The accuracy, or in accuracy as the case may be, was when they described two clear misses at 500 yards and then with the results so poor at 1000 yards they simply gave up trying to ascertain accuracy.

 

18 years of shooting tank main guns at targets and other tanks, and I don't recall every saying, "Damn, this gun is just too accurate".

[Mobius]

I was being sarcastic.

I mean it understates the round to round dispersion by not including laying error.

But look at page 12 random error section. It is composed of round to round dispersion and laying error.

When the Russians fired at a target they didn't draw the bullseye in the center of the spread after the shoot.

http://tankarchives.blogspot.com/2013/02/accuracy.html

Edited January 21, 2014 by Mobius

[Edmund]

I was being sarcastic.

I mean it understates the round to round dispersion by not including laying error.

But look at page 12 random error section. It is composed of round to round dispersion and laying error.

When the Russians fired at a target they didn't draw the bullseye in the center of the spread after the shoot.

http://tankarchives.blogspot.com/2013/02/accuracy.html

 

 

Am I missing something? When I read the link I get the impression that the Soviets fired at a target. Then they drew a circle around the 5 most accurate shots and a circle around all shots. I read that as closest together. It may not be what is meant. How do we even know they came close to the original "target". Presuming they shot at something. Were adjustments made after each shot in the German or Soviet tests? It would also be nice to know the order of the shots. I know nothing about ballistics or firing tests. Just wondering. I would like to see results of tests of the three guns conducted the same way. Better yet all WWII and Cold war guns. I like numbers and comparing things. I am not saying that soviet guns are not accurate. They may be the best. Just it would be nice to see comparable tests (These may be, but I wouldn't know).

[Mobius]

From looking at the Russian test some shots were way off to the left side in upper test then off to the right side in the lower target. If this was run like the US test the center would be moved to the left in the upper test and moved to the right in the lower. Of course, I don't really know how things were done.

[DKTanker]

Am I missing something? When I read the link I get the impression that the Soviets fired at a target. Then they drew a circle around the 5 most accurate shots and a circle around all shots. I read that as closest together. It may not be what is meant. How do we even know they came close to the original "target". Presuming they shot at something. Were adjustments made after each shot in the German or Soviet tests? It would also be nice to know the order of the shots. I know nothing about ballistics or firing tests. Just wondering. I would like to see results of tests of the three guns conducted the same way. Better yet all WWII and Cold war guns. I like numbers and comparing things. I am not saying that soviet guns are not accurate. They may be the best. Just it would be nice to see comparable tests (These may be, but I wouldn't know).

 

The Soviets were measuring round to round dispersion, the aim point is immaterial, how close together are the impacts is the concern. The reason they aren't particularly worried about accuracy (how close to the actual aim point) is because the sights can be adjusted to the shot group, thus making the system accurate. No, their concern was with precision, the ability to repeat an event. Once precision is achieved then accuracy can be delt with.

 

As stated in the text, the Germans used a 2.5 m x 2 m panel to test accuracy. In other words, if the Sovs adjusted the sights (zeroed) for the D-25 and repeated the shot group on a German panel, they would have achieved 100% accuracy as would be measured by the Germans.

[Edmund]

I wasn't trying to attack you. I just had questions.

[Colin]

The aimpoint is important to dispersion as a common point of aim removes operator induced errors so you get a better picture of what the gun/ ammo is capable of.

[Mobius]

As stated in the text, the Germans used a 2.5 m x 2 m panel to test accuracy. In other words, if the Sovs adjusted the sights (zeroed) for the D-25 and repeated the shot group on a German panel, they would have achieved 100% accuracy as would be measured by the Germans.

 

The only reason for that is the peculiarity of Russian dispersion. They are wider in the horizontal than the vertical. The Germans are the opposite. So if the German target was reduced to 2m x 2m their results would stay the same. If the Soviets used that shape target one shot would be wide.

Edited January 23, 2014 by Mobius

[DKTanker]

 

As stated in the text, the Germans used a 2.5 m x 2 m panel to test accuracy. In other words, if the Sovs adjusted the sights (zeroed) for the D-25 and repeated the shot group on a German panel, they would have achieved 100% accuracy as would be measured by the Germans.

 

The only reason for that is the peculiarity of Russian dispersion. They are wider in the horizontal than the vertical. The Germans are the opposite. So if the German target was reduced to 2m x 2m their results would stay the same. If the Soviets used that shape target one shot would be wide.

 

Sure, if you make the standards tougher the measured results will appear to suffer as a result. But why change the standards after the fact?

[Mobius]

The aimpoint is important to dispersion as a common point of aim removes operator induced errors so you get a better picture of what the gun/ ammo is capable of.

Right. From the reports I've read is that they can zero out systematic errors but not random errors.

[Colin]

I understood at some point they figured out that the petals were causing some of the errors, when did they find that out?

[Mobius]

I found this link today to a Rheinmetal Weaponry Handbook pdf. I hope it stays up for awhile.

Shows the connection to average dispersion, std deviation dispersion and 50% zone (ala German style). Harry Panash posted it awhile back.

http://worldtracker.org/index.php/?option=com_wrapper&url=/media/library/Law%20Enforcement/Handbook%20on%20Weaponry%20-%20Rheinmetall%20-%201982

[Manic Moran]

Part 2.

 

http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly2/

[Manic Moran]

I understood at some point they figured out that the petals were causing some of the errors, when did they find that out?

 

I don't know, but the fix wasn't applied until 1954.

 

Interestingly, it said that it wasn't necessary when the same projectile assembly was fired from 77mm. Evidently there was some particular velocity which 77mm didn't reach but 17pr did which caused the separation problems.

[shep854]

Part 2.

 

http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly2/

'Flash-back'? That should add excitement and adventure to a loader's life...

[DKTanker]

 

Part 2.

 

http://worldoftanks.com/en/news/21/The_Chieftains_Hatch_Firefly2/

'Flash-back'? That should add excitement and adventure to a loader's life...

 

Not fun, also a not uncommon occurrence with the M256 120mm, though it seemed some cannons and ammunition lot #s were more prone to it than others, I never had the chance to experience the fun. What made it particularly "fun" on the M1A1 is that it would also set off the automatic fire extinguishers.

Edited January 25, 2014 by DKTanker

[Panzermann]

Only heard of one back fire of a Rh120. And that was because the rubber seals of the bore evacuator were old and totally worn out and torn. But must have been a sight to behold.

 

 

Or maybe us young tankers this story was told so we clean and inspect the bore evacuator rigorously.

[shep854]

Only heard of one back fire of a Rh120. And that was because the rubber seals of the bore evacuator were old and totally worn out and torn. But must have been a sight to behold.

 

 

Or maybe us young tankers this story was told so we clean and inspect the bore evacuator rigorously.

Not to mention correct ammo stowage.

[Froggy]

only suffered a back fire on AMX30 with 105mm, while firing very old HE ammo (there were older than me by 8 years)