Yes, the Garand muzzle flash does amount to great big ‘Hidy ho!” to your opponents. The FAL is a bit more discreet in that regard.
I do have a small collection of AR15 types just for the reason that you mention. But I qualify at the local Appleseeds with the FAL. I’ve bee ntempted to take the Garand, but the mag changes that some exercises require are too fidgety for me. The Grarand’s designed to shoot 8, reload and then shoot 8 more. Yeah, I know there are 5 and 3 round ‘sleds’ but I never got around to getting them.
Been saving my stash of 30.06 Lake City black tip for the inevitable rainy day.
Try the Remington 125-grain *reduced recoil* load. It doesn't shoot to the same point of aim as full-house ball, of course, but at night that's not a big deal. And a slotted M1D-type flash suppressor, much like those on the British inch-pattern L1A1 FALs helps too.