Well, I'll tell you. I get decent/satisfactory groups out of M855 with my Sport. I get somewhat less decent groups out of the 193 (55 grain). The 855s seem more consistent. That goes for my 20" SGW also, which is a 1:9 SS barrel. With the 193s, my groups opened up about an inch, and I'd get an occasional flyer at maybe 2".. so, I don't shoot much 193 anymore. But I don't shoot much 855 either, as I'm a handloader. That's what I found though.

What works the very best in both are my handloads, which are 60 grain Sierra Varminter hollowpoints (Sierra #1375). Very nice groups; tighter than either the 193s or the 855s.

I figure, shooting with an EoTech that has a "1MOA dot" and no magnification, a baseball-sized group at 100 yards is just fine. It will do the job that the rifle is made for. If I want to shoot bullseye or want to really reach and touch someone/something, I have other, more suitable armaments.... and I want to stress that I feel the Sport and it's barrel are very capable of doing that with the correct optics on board.

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Roger
USN, Retired, NRA Lifer