Well that's not good, maybe you have a worn out or sub par barrel.I’ve tried many bullets in my AR10. Off the top of my head 147 fiocci fmj, 150 hornady fmj, 150 Speer hotcor, 155CC, 165 hornady interlock, 168CC, 168 horn BTHP 168 eldm, 175SMK, and 178 eldm. Probably missing a couple.
My best groups are with the 168CC, and the best overall performer is the 168 eldm, so that’s what I shoot. But if someone asks about a bullet I have experience with, I’ll let them know.
I did a round of load development with the 150 FMJs and had a sub Moa load. It was clear they weren’t a top performer, so I loaded the rest of the box at the best charge and used them for practice. My experience with them is what it is. They aren’t match grade, but decent enough for practice ammo, and you can probably get them to shoot as good as any factory ammo with some load development. As opposed the the 147 fiocci, I have 950 I don’t even care to load because at 4 MOA you can’t even tell if you’re “doing your part”.
We use 168g smk gmm as a standard to go by. The factory rounds are a known benchmark.
They also load easily with varget and are fairly jump tolerant.
If it won't shoot that I would consider a new barrel.
Also since you have a collection of different ammo you may want to consider an E C Tuner Brake.
I never knew an ar could shoot 1/2 inch groups with me driving.
It may not take all the slop out of store bought but it will make a eisily measurable difference .