I too just got a 527 in 223. Mine is a M1 American topped with a Weaver 3-9X38 scope.
I was shooting The Remington / UMC 45 grain JHP out of mine and it worked great.
I then tried some 55 grainers from Hornady, Federal, and remington.
The Hornady was the ballistic tip, the Fed was FMJ with a boat tail and the Remington was soft point.
Out of the four.... Have to go with the Bulk Rem for my rifle at 100 yards.Nice tight group about the size of a quarter off of the bench with out a rest.
The others were a little larger. I used what I have for my other 223's. Really like this little rifle.