May I behold to you the M3 GMC (Gun Motor Carriage)
A perfect event/prem APC for the US to match up with the germans 251/9
armed with a single 75 mm M1897 gun.
and while I can’t find any historical photos of it seeming an 50 cal on the back:
Im not a fan of proper guns on APCs because at some point they just arent an APC but a tank destroyer or etc.
The stummel is only acceptable for me because allied tanks quicky get so much armor that the stummel cant even do anything to them.
But the M3 would be penetrating every single axis tank without a problem as those only start getting well armored in BR4.
If you allow a halftrack that removed their benches in favor for mounting a gun ontop to still be an APC then you will quickly run into the problem of tank riding.
Lots of nations had troops riding ontop of tanks so you could make a case for those tanks beeing an APC aswell.
If you allow everything to be an APC then you should allow this to be an APC aswell.
All of those examples arent even hard to find as there are plenty more pictures on he internet.
I know that the stummel is still problematic but adding more upgunned APCs wont improve the situation either.
Again APCs are NOT meant to fight tanks unless forced to, all of these types of cannon armed APCs should be BR 3 or above otherwise they would make other APCs pointless.
It is a mobile rally point that can sling a couple of HE shells at enemy infantry and you should use it as such, there is a reason it doesnt occupy the tank slot.