Change in AR accuracy after inital load work up

[Randy57]

I have an AR 15 with a S.Steel bull barrel from Rock River that I have had for a year. I broke it in slowly and I worked though a few dozen initial loads and got a great one that resulted in a sub MOA at both 100 and 200 yrds. Recently I noticed a loss of accuracy at both ranges with this load. Tried a new reduced load today and got back the sub MOA at both ranges. Does any one know Why it changed? I keep the barrel spotless could it be a change in the Harmonic or Vibration node as it seasoned? The new load is working great??

 

[Boyd Allen]

Throats get longer as they wear, increasing bullet jump, affecting tune. Was the ambient temperature that you worked up the load in the same as when you tested recently? Temperature affects tune. I get tickled when I hear someone talk about working up a load, as if it was a one time and you're done thing. This only works if your accuracy expectations are relatively low. I am pleased to hear that you found a load that has restored you rifles accuracy. If it is very slow, and you have some room in the upward direction, from your old load, you also might find that a half grain hotter might work too, but of course I would caution against the highest bolt action pressures in an AR.

 

[Randy57]

Thanks a lot! Great info and you're right I guess I expected the load to work forever! Never thought about the overall ambient temperature per se. I worked it up in the cooler weather and living in Fla it never stays cool for long!! The original load was near max and the load that works now is 1.2gr less same OAL and bullet. Shooting is fun and always a challenge for perfection. Again thanks.