20 rd mags are half a lb each. aluminum scope bases on M1A soon wear loose, the steel one weighs a lb. so does a decent scope, so does the bipod most such fools choose. Other 308 AUTOS, or the non\-match M1a, or the match M1a WITHOUT match ammo, have ZERO range advantage over the 223-AR. the standard M1A is 9 lbs, glass stock adds wt to that. heavy barrel adds a LOT of wt to that. So, 9 lb 308, 2 lbs of scope and mount, 2 lbs of spare mags, 6.5 lbs of 308 match ammo (100 rds),1 lb of bipod. and you STILL need a sidearm, and 22 pistol for foraging. Those total 5 lbs or more, counting holsters, ammo, spare mags, mag pouches, etc. THAT'S why you only carry 100 rds of 308 ammo.
without a can on the rifle, and being in open country in daylight, firing at too great ranges, or guys you can't SEE (using "cover") being too tired to be properly careful, etc, you'll NEEED to fire a lot of 308's, too. Then you'll get killed, and you'll DESERVE it. stupidity like THAT SHOULD be fatal.