[willfully armed]

Number 1- you don't have a target rifle. That's a "service rifle".

I built a "target" AR about 5 years ago. RRA receiver set, bolt and LPK with 2 stage match trigger. LMT SOPMOD stock, yhm free float 4 rail. Put a cheap Vulcan 16" .970 stainless fluted barrel. And a cheap 12x Bushnell Scope.

It would put 62gr Wolf into .400 groups at 100 yards.
My new barrel is a WOA 18" SPR. It runs MK262 at .375-.400 groups all day long.

Long story short, your gun isn't really setup to do what you're expecting. I'm assuming here, but maybe you don't have a great technique for precision shooting yet either.

Breathing control, form, trigger control... It takes practice.

 

[willfully armed]

Shooting reloads doesn't automatically mean you're going to get good groups

Bug hole groups require extensive load development.

Bullet weight
Seating depth
leade length
Powder
Charge weight
Primers
Good dies.

You can develop a load for weeks and only get a 3/4-1" group, just to change primers and have them shrink to .375"

Seating from .010-.015 off the lands can make a huge difference.

I'm not doubting your ability, just providing possible answers