Battle rifle of choice for me is the Springfield M1A standard. .308W/7.62x51NATO. Plenty of 20-round magazines, the USGI stock (modified for enhanced rigidity). Some tweaks done to make it more accurate, consistently shoots about 2.5 MOA with NATO ammo, 1.5 MOA with match ammo. Topped with a Millett 4×16 mil-dot scope (quick-detach mount). Packs a punch, proven battle-field weapon and reliable. Downside is that it is heavier than AR-15/AK platforms, but that’s a trade-off I’ve decided to make.
I have others… but this is the SHTF/TEOTWAWKI weapon. Big and brutal, admittedly, but effective.