I was wondering about the physical properties of cartridge cases made of steel. Can steel cased ammo be loaded (I'm not saying handloaded) to the same pressures as brass cased ammo? This leads me to my next question. If steel cased ammo is cheaper, why is it that only few manufacturers use it and why do most armies use brass cased ammo? Hope you guys can enlighten me!
I believe steel case ammunition could be loaded to higher pressures than brass just based on the material properties of steel.
Someone would actually have to do a stress analysis of the pressure vessel given data on the strength of the particular steel at the hardness levels used for a cartridge. Hardness varies throughout the case and that makes a difference on strength. Still, it is hard to believe that any steel case would not be stronger than brass.
Rupture strength is not the issue. The primary reason you do not see more steel case use is breech friction.
Steel cases were used in WW2, these were coated with a chromate coating for rust prevention. The Army had so many issues with stuck cases that in the 50’s there were tests run with steel cases coated with Teflon and wax. The coatings improved the function but, if my recollection is correct, they still were not better than brass cases.
Steel cases do not retract off the chamber walls as much as brass for the same pressure levels. This is very important as virtually everyone has experienced a stuck case. Steel cases stick more often.
Steel on steel also creates a lot of friction.
What you want in automatic mechanisms is a low friction case. The only friction you need is the friction necessary to keep the case from collapsing or from being pulled up the barrel by the friction of the bullet inside the case neck. Apparently there is some friction needed for brass cases. However, once the combustion is done, you want that case to peel off the chamber with no effort at all.
Given the tolerances in cases, chambers, steel cases do not function as well as brass cases.
If the weapon is designed with steel cases use in mind, function can be quite good with steel cases. I believe the AK47 was designed considering the use of steel cases, and that rifle runs steel case ammunition quite well.
I have seen a number of shooters using steel cases in the AR15. The 223 round was a wildcat developed at Bob Huttons ranch by a bunch of guys who were trying to get 3000 fps with a bullet. It was not a highly analyzed or tested cartridge when it went into service with the AR15/M16. The rifle was not highly developed either. The service rifle has always fired brass cased ammunition. Given the past history of both cartridge and rifle, it is no surprise that I have seen a lot of malfunctions in the AR15 with steel case ammunition.
I have not conducted any extensive testing on this, but I am of the opinion that legacy actions built and designed around brass cases will not be as reliable with steel cases as they are with brass cases.