Re: FN TSR USA .223
The samples I have shot prefer the heavier bullets. I have shot as light as 45gr and as heavy as 77gr. Accuracy always increases as I went up in grain weight. The best groups I have gotten out of a TSR-XP USA is with Federal GMM 77gr, near 1/2 MOA. It also likes the 69 gr version, but not as much: consistant 1 MOA.
I was surprised because the twist rate is 1:9. Can't argue with the bullet, though. If you own a TSR-XP USa, give some 77gr bullets a try.
Hope this helps.
Semper fi,