AR's are picky

[.444 Marlin]

Untill you find that sweet spot. When I first started loading for my RRA, I couldnt find anything that would shoot better than 1" at 100yd or even 50yd but I got to tinkering with the seating depth and found that if the bullet is just barely off the inner wall of the magazine then that is about as close as I can get to the seating depth the rifle likes. I havent shot these loads at 100 yet but my 50 yard groups decreased in size by almost 1/2. Even the lighter bullets around 50-52gr are workin pretty good. Out of the 4 or 5 powders I have tried in this gun, BenchMark and the camp perry powder AA2520 work the best. I dont have the actual seating depth for each bullet because each bullet is different in length at the ogive but if all are seated to just off the inner wall of the magazine then they all should group pretty close.

.223 Remington
Winchester Brass
CCI SR primers
60gr Hornady SP & 60gr Hornady V-Max
26.4 AA2520 (Max load, no signs of excess pressure after shooting)

and

52gr SMK over 24.5gr Benchmark (1.0gr below max)
I dont have pics but my 50yd groups averaged around 1/2-3/4" which is more than enough for yote hunting around here and general plinking. All loads cycled fine.
I tried 2 different factory loads in it also, one was PMC 55gr FMJ, grouped fine, and cycled fine. The other was el cheapo Wolf 55gr FMJ, cycled fine, and grouped fine BUT they smoked like crazy.

 

[firefox]

Did you crimp?

 

[.444 Marlin]

Nope. I never have crimped cases. Not even on the .444 marlin or my .45-70.

 

[firefox]

Usually if I crimp the case into the bullet(even if it isn't cannelured) I get better groups than the same load standard seated. I also get higher velocities with less powder. My brass doesn't last as long since the necks usually split around the fifth sizing.