I've never used anything but 7.5's in 223. They came highly recommended, worked great, so I never looked into primers any further. I'll push the loads to a grain or so over "max" in the loading manuals, for rifles. .5 grain in pistols, with the slower burning powders. With the really lw bullets, 50-70 grs in 9mm or. 45, with the huge hoillowbase cavities, you have to use so much Bullseye, just to get the slide to cycle reliably, that it freaks out people who "think" that they know something about reloading. I mean 6-7 grs of BE in a 9mm, 12-13 grs in a .45. Gotta have a fully-supported barrel and tough, thick brass cases, tho. I had loads that were perfectly safe in a p35, blow cases every time, fired in a Taurus copy of the Beretta. Badly unsupported at the feed ramp. I welded it up and recut it for optimal support, still bulged those cases badly.