"For trials the M2 Bradley has already been fitted with a 35mm Bushmaster III automatic cannon, and a 50mm version of the same gun (same cartridge case). 40-57mm automatic cannon are becoming very popular as projects; because they give you the ability not only to spew out infantry destroy HE rounds, but also to destroy older tanks and any IFV or APC at extended ranges. Telescopic cased ammunition, with the shell buried inside of the cartridge case, make that sort of cannon a lot more practical then it once was. The result is fatter ammunition, but its also much shorter, which lets you build a shorter bolt and chamber and thus a generally much more compact gun."