Post by wfa on Jan 30, 2015 13:01:55 GMT -8
The 75gr A-Max is a good shooting bullet, but who wants to single load a "gas gun"? The five "ASC SS" mags I have will accept cartridge length of 2.30 inches without any problem, so I set off to see if I could make the A-Max feed at that COAL. Loading data was, of course, non-existent, so I selected a starting load for the 223 Rem using H4895, CCI 450 primers (thicker cup than the CCI 400), and Norma sized/trimmed once fired brass. The rifle has a BHW 18" Slim profile barrel with a mid-length gas system, BCM upper receiver, RRA bolt.
Bullet jump was obviously going to degrade accuracy, but how much? All that "free bore" (.155+ inches) should lower pressures, but would it? Short answers: Yes, and yes. Although I went to 24.5 gr of H4895 with no signs of excess pressure, I settled on 24.2gr based on accuracy. TEN SHOT groups are in the 1.125 to 1.0 MOA at 100 yards w/4X scope. The powder in this load is slightly compressed, but not very much. Of all the loads fired, EVERY ROUND fed perfectly; there were no failures of any kind.
Next step was to see how these loads did in a "conventional" rifled barrel; I wanted to check for pressure signs and velocity differences. The BHW is my only 18" upper, so I used a 20" barrel upper for comparison. This upper has only "BUIS" installed, but I wasn't too interested in accuracy. Accuracy turned out to be "just fine" given my old eyes, the sights, and the target I was using. Again, I had no failures of any kind. Pressure signs were marginally greater, but not enough for me to be concerned about.
Chronograph Results:
18" BHW, 1:8, 9 shots (Chronograph only works when turned on):
HI: 2783
LO: 2726
ES: 57
SD: 18
20" FN 5.56x45 chamber, 1:7, 10 shots
HI: 2861
LO: 2812
AVG: 2838
ES: 49
SD: 14
Draw your own conclusions. Clearly not a viable "match load" for a "Master", but for someone that wants to be able to tell "shooter error" from "flyers", I think it will work for me... and I don't have to "single load".
Bullet jump was obviously going to degrade accuracy, but how much? All that "free bore" (.155+ inches) should lower pressures, but would it? Short answers: Yes, and yes. Although I went to 24.5 gr of H4895 with no signs of excess pressure, I settled on 24.2gr based on accuracy. TEN SHOT groups are in the 1.125 to 1.0 MOA at 100 yards w/4X scope. The powder in this load is slightly compressed, but not very much. Of all the loads fired, EVERY ROUND fed perfectly; there were no failures of any kind.
Next step was to see how these loads did in a "conventional" rifled barrel; I wanted to check for pressure signs and velocity differences. The BHW is my only 18" upper, so I used a 20" barrel upper for comparison. This upper has only "BUIS" installed, but I wasn't too interested in accuracy. Accuracy turned out to be "just fine" given my old eyes, the sights, and the target I was using. Again, I had no failures of any kind. Pressure signs were marginally greater, but not enough for me to be concerned about.
Chronograph Results:
18" BHW, 1:8, 9 shots (Chronograph only works when turned on):
HI: 2783
LO: 2726
ES: 57
SD: 18
20" FN 5.56x45 chamber, 1:7, 10 shots
HI: 2861
LO: 2812
AVG: 2838
ES: 49
SD: 14
Draw your own conclusions. Clearly not a viable "match load" for a "Master", but for someone that wants to be able to tell "shooter error" from "flyers", I think it will work for me... and I don't have to "single load".
