re: Does anyone own a WW2 Era Browning Assault Rifle?

I think the ammo was actually a little weaker than todays stuff. I heard you can't shoot todays ammo in the M1 Garands either

Partially correct. 30/06 ballistics of that time were 150 gr bullet at 2700 fps. Today it is 2900 fps. But it is not the power of the modern rounds that is the issue. It is the pressure curve of the modern slow powders that can damage the piston rod of the M-1 Garand. If you use the proper medium burn rate powders (IMR 4064 or 4895), you can load to modern velocities and they are fine in the Garand. Hornady makes a special 30/06 Garand load that uses the proper powders. What will damage a Garand is a modern load with the slower powders like IMR 4350 or 4831.