I had the chance to do some blasting this weekend, Saturday and Monday actually. I was shooting the Oly, 11.5" bbl with long flash hider. Anyhow, Saturdays fodder was Winchester white box 5.56. I ran out so on Monday I switched to Federal XM193. Both days it was overcast, similar weather. I was freekin amazed at the difference btw the two loads. The Winchester (which is what I'm used to) creates just a bit of flash noticable on the hider slits. On the other hand the Federal shoots a flame about two feet long for the hider! My wife commented after she fired it, 'it's like shooting a flamethrower!', and it was. The Federal seemed to have more 'kick' as well.... for an AR anyhow. For what it's worth I used one of those british mags the whole time, it worked flawlessly.