I read this in the OP:
The local range doesn't permit M2.
So this does not make sense:
I've never heard of a range that bans lead core 30 caliber ammo. are you sure the guy didn't think you were talking about penetrator ammo(black tip)?
Most M2 ball surplus around (whether USGI or Greek HXP) has a steel jacketed bullet; it attracts a magnet, therefore is banned at many ranges.
The M1-specific ammo from Hornady is copper jacket; CMP sells them but they are months behind right now. Both loads run in my rifles. Not sure about the Federal AE M1 ammo, since Federal might have some steel jacketed 7.62NATO bullets around.
Also, the Greek HXP ammo is a little hotter than USGI M2 ball, but really, the later USGI was made weak and the HXP is normal.
That said, probably a gas or spring problem. In addition, is it possible that an adjustable gas nut was already installed and it has been adjusted so your ammo does not work?