Federal 55gr seems to give large groups - the Remington 55gr stuff is pretty good
if you want the ultimate, treat yourself to a box of Creedmore stuff from the CMP
https://estore.thecmp.org/?cat=AMC
I have not checked the prices but this was a good deal for match ammo while back. Be careful creed more now offers "recondition" ammo using LC brass. At least on the 308/30-06 stuff vs lapua on the new stuff.
Following is a list of ammo that has done well by me and was a good price. This was before reloading.
Just remember if you find a particular ammo you and your rifle like try to buy as much as that lot# as possible.
1. PPU M193
2. Wolf gold...even recent purchase was good shooting. Hard to pass up good brass ammo for .29 delivered.
2. Wolf gold with 77 grain bullet. Not seen this for a while but it was .36 each
3. PPU match seen it out on the web recently .38
4. Remington 55gn soft points green and yellow box. On sale most places just before hunting season.
Other than that most "bulk" ammo sucks.
After shooting many brands over the crony it's easy to see why some bulk does not do well.
Fed M855 was the worst over the crony. Even getting beat by some early 80s Norinco silver box.
Bullet quality is another thing.
Like I said you pull down some ammo and you will see.
If your getting dime size groups with a particular weapon with a particular ammo don't waste or foul that barrel shooting other ammo that does not perform.
Another thing to consider is when you change bullets/ammo it may multiple rounds before your rifle bore gets "seasoned" to the different bullet.
I went through this reloading. Was having a awful time testing loads and bullets. Someone here on NES suggested not to test different bullets in one session. Clean the bore first or shoot 10 shots of the new bullet before trying for a group. I opted to give the bore a scrub between bullet changes.
So those expensive match bullets went from WTF to nice little nuggets like I was hoping.
My "match" ar seems to like 77s loaded to mag length the best.