I had the good fortune of being able to shoot today, and used the chance to collect some Chrony data.
I shoot the following rounds from a 16” (gasp) Model 1 upper. It was a blistering 40°F. Not bad for February 1. All strings were five shot.
Radway Green M855
Extreme Spread 64.87
Standard deviation 27.20
Extreme Spread 79.41
Standard deviation 32.49
Brunell 62grain Hollow Point
Extreme Spread 47.23
Standard deviation 26.85
Wolf 62 grain FMJBT This is the older and obviously slower stuff
Extreme Spread 102.4
Standard Deviation 41.94
M855 Clone using Reloader 7 @ 21.5 grains and ss109 62 grain bullets
Extreme Spread 83.34
Standard Deviation 30.61
From they way the spent cases ejected I would have guesses this was a much slower load than it turned out to be. The empty cases literally fell at my feet. According to my manual (which is quiet old) this is the max load. But I think I will bump the charge up a grain or a grain and a half to see if I can get to 2850FPS.
The following round I shot from a 24” bull barrel. I was not going for groups but it did look like they had potential.
Black Hills 68 grain match boat tail hollow point.
Extreme Spread 89.24
Standard Deviation 39.94
Thanks for looking thebrain
Not at all surprising. Port pressure and dwell determine bolt carrier movement parameters. RL7 is a bit fast on the burn scale - faster even than IMR 3031. I would guess that something slower like 748 (or even H335) would give more forceful ejection (higher port pressure).
Thanks for posting the data!
ETA: Pls, pls don't assume that b/c ejection is weak you must be below maximum pressure. To take the analogy further, you would KB the gun before you could get the gun to cycle even once using Alliant Bullseye.
Thanks for the insight.