Yoozername wrote:Yes, AP rounds have different packing than HE rounds, and sometimes different propellant also. But, even crimped rounds can be wrestled out if care is taken. And, yes, there is some information regarding that incident but it was actually M72 rounds I believe. And they reweighed the powder precisely. It was found to be varying.
Yes, I should read my own manuscript occasionally. I'm afraid the account you found was a bit "dressed up" though. The more likely version is in Hunnicutt,
Sherman pp. 89-90:
During the development period of the APC M61, it had been necessary to introduce an interim round to meet the requirement for large quantities of armor piercing ammunition. This was the AP M72 monobloc shot. Rushed into production, this solid steel shot was variable in quality and tended to break up against face- hardened armor.
Tests carried out near Cairo in March 1942 against several German tank hulls re- vealed that the M72 shot was relatively ineffective against the frontal armor at ranges over 500 yards. A successful effort to provide effective armor piercing rounds resulted from the brilliant idea of Major Northy, an Australian serving with the British Royal Army Ordnance Corps. Early in 1942, about 50,000 tons of assorted German ammunition captured during the relief of Tobruk were moved to the Ninth British Army Depot along the Suez canal. Among this vast supply were many of the explosive loaded APCBC rounds for the Panzer IV’s 7.5cm Kampfwagenkanone (KWK) L/ 24. Major Northy noted that if the rotating band was modified, the German projectile could be fitted into a U.S. cartridge case and fired from the M3’s 75. Checking with Major G.B. Jarrett, an Ordnance ammunition expert with the U.S. Mission in the Middle East, he found that Jarrett not only agreed as to the feasibility of the project, but gave it his enthusiastic support.
The German projectile differed from its U.S. counterpart in having a much wider and thicker rotating band, but the basic dimensions of the round were essentially the same. A number of the German projectiles were removed from their cartridge cases and the rotating bands turned down to the U.S. dimensions in a lathe. The rounds were then success- fully assembled into U.S. cases and they chambered properly in the M3’s 75mm gun. These were explosive loaded armor piercing projectiles fitted with a base detonating fuze. This fuze was armed by the projectile rotation when the round was fired. Fortunately, the lathe rotation was insufficient to arm the fuze during the machining operation. Some of the converted ammunition was test fired against a Panzer III hull in comparison with a few of the new U.S. APC M61s which had been flown out to Cairo. Like the German round, the M6l was fitted with an armor piercing cap, but it was inert loaded since the development of a suitable base detonating fuze was not yet complete. The tests showed the penetration performance of the two rounds was identi- cal, but the damage resulting from the German projectile was much greater. Both penetrated the front of the Panzer III at a 1000 yards, but the German round exploded inside the tank. In combat such an explosion would almost always set off the stowed ammunition. With the approval of Middle East Headquarters, the new round was designated as the 75mm AP- Composite and conversion began at full speed. A total of about 17,000 rounds were converted of which 15,000 were the explosive loaded APCBC. The remaining 2000 were high explosive and smoke which were also modified as any reliable round was most welcome for the M3’s gun. U.S. AP M72 and HE Mk I ammunition was used to provide the primed cartridge cases and propellant charges.
Much of the old ammunition was found to contain variable weights of propellant so all the charges were dumped together, mixed, and re- weighed to insure a uniform muzzle velocity. The conversion work took two to three weeks and the composite rounds were sent forward before the action opened on the Gazala line in late May. No information seems to be available on what use was made of the new ammunition. About 6000 rounds were captured by the Germans in the dumps at Capuzzo during the retreat to Alamein. They were then moved to the German base dump at Tobruk where they were recaptured the following November
And, as far as those marines, they should have consulted the cannon-cockers...IF they had taken the projectile, and used a ram-rod of some invention, they would have gotten a nice shot. The ram-rod makes the rifling bite into the copper and that would make a seal...
Um, it was Betio, they didn't have the time and luxury to separate the projectile and case in order to ram the projectile.