Truth be told, that’s from a bolt action- a Ruger precision rifle, shot prone from a bipod and a fortune cookie, with a vortex razor gen 1 5-25. But, it was fed from a Magpul pmag. And, that ammo is money in a 6.5 creedmoor lr-308 that I built for my dad, but I don’t have any groups from it.
Federal gold medal berger (130 gr) also shoots great and fits in a pmag.
All that is to say that you shouldn’t feel constrained by loading to mag length in a large frame AR.