A cut down BAR must weigh at least 14-15 lbs. I wouldn't want to carry it very far.

The FAL packs about the same power in about half the weight. It's fine for single shots but almost uncontrolable full auto. There are some heavy barrel FALs that split the weight difference. I hear they work pretty well on a bipod.

If you need more fire power than that, you have to step up to something like a M-60, MG-42 or 1919A4 belt fed beast.