Yoozername
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quote:
ORIGINAL: Mobius
page 23
I find it fascinating that the Germans did indeed, vary the powder charge to test projectiles at different velocities. Basically, they seem to have standard plate thickness (40mm, 80mm, 120mm, etc.) and have to test around these. They certainly seem intent on developing formula to generate the full penetration data across the range of the weapon. In other words, the penetration curves, penetration vs. range, are largely calculated from careful testing of just several points. They are not setting up armor at all those ranges, of course.
The generation of Gz at first seemed odd. But this is important if they would want to check for reproducibilty later on. The use of 'known good' or test projectiles is also important. Basically they want them constant so they can take that variability out of the test. I think Rexford took that to mean he could devalue production AP shells for some reason. From reading his book, I can't determine if he had this full report or just snippets from other peoples posts.
Again, the Germans really believed in the APCBC as a delivery agent for the HE charge. They seemed to insist on the penetrator staying in one piece and entering the armored target. The Gd testing showed that this was a criteria. The Germans basically wanted to confirm that the gun under test would penetrate a standard armored plate up to 5 times for this caliber. They actually had more stringent tests for smaller calibers (10 shots). Once they resolved the minimum velocity needed to just penetrate the target armor, they selected the highest velocity of the 5. I suppose as a buffer. They may have actually added an additional amount of powder to ensure that the penetrator had residual velocity. I have read somewhere it was 5%. I am sure that the powder to velocity relationship is not completely linear but at small increments it may be taken as nearly linear.
While the document states that this was an example given to the British officer doing the investigation, it is just suspicious that it is indeed one of our 75mm subjects. The initial velocity aimed for, 750m/s, is shown to not meet the velocity or penetration criteria. They must certainly have powder-to-velocity charts and vary the powder weight to increase velocity. They initially over-shoot to 780m/s and then actually get 756m/s and it does not penetrate the plate acceptably. They then hone in on 780m/s fitting the bill.
From the test, they can conclude that a muzzle velocity of 780m/s will penetrate the armor at set range and angle (something like 120mm@30 degrees as an example). They also conclude that 710m/s will not. They can extrapolate the 710m/s downrange to a certain range also. That is, the weapon firing at a muzzle velocity of 780m/s will at some point be downrange and lose velocity and have the same results asthe 710m/s test. They may have had more shoots for a gun's initial testing. Certainly testing battlefield ranges like 500m, 1000m, etc.
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RE: German 75mmL43, L48 and L46 velocities - 
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