I have a PSA 16 inch upper on a S&W lower. Wolf steel case .223 55 grain is very accurate. Federal brass 556 55 grain is all over the place. My Ruger AR shoots the Federal fine. Doesn't make sense to me

Have the barrel re tightened? True n glue? What optic?

Bushnell elite 3000. Proven good scope.

Clean it thoroughly and lube.

Double check scope rings and mount.

FMJ ammo, especially steel case is not expected to be accurate. 3 moa is common, sometimes worse.

If you have a muzzle brake remove it. Inspect it closely for bullet strikes, copper marks on the interior.

If your rifle won't shoot 69 grain Federal Gold Medal Match into tidy little groups you probably have a gun problem. I became so disgusted with ball ammo I stopped buying it 35 years ago. It is the worst ammo on the market.

Front and rear bags are required for consistent accuracy testing. I use an Uncle Bud's bag up front with either 2x8 pieces of wood or rubber sheets to achieve the elevation I need. I use a Protektor rabbit ear bag in the rear and shim the height as well.

It's important that the rifle is perfectly aligned on target for each shot without me applying pressure to steer it. I then concentrate on my breathing and trigger pull.

Some barrels are simply finicky. If your rifle shoots Wolf fine I would count your blessings.

I own a Springfield Armory National Match M1 Garand that never shot well even when it was new. I decided to have it completely rebuilt and rebedded with a new Douglas barrel. That rifle still doesn't shoot very well.

The nature of firearms and barrels is that each one is an individual. Some are picky about what you feed  them and some are not.