450Bushmaster.net

Hello. First time posting on this forum, bit very active on others. I am primarily a bolt gun guy, but I'm working on developing loads for a friend for his 450 BM for MI hunting. I wanted to start by saying that I do not believe that my problem is a reloading problem, I think and hope that it is a buffer weight problem. Here are the details of the issue and what I have done so far:
1. The point of impact shifts significantly between the first shot of any string and then shifts back on the third shot.
2. The shift is aprox 3-5 moa between the first and second and then almost returns to original point of impact from the first shot.
3. The problem has been consistent over two different 450 uppers onnthe same lower.
4. The problem has been very similar when shooting 250 grain factory ammo and 160 grain reloads.
5. The problem has persisted between two different scopes.
6. *** The problem goes away almost 100% if I load one round in the mag, put it into battery and shoot, and then repeat two more times. So, I am replicating the same feeding scenario with each shot.
7. All groups referenced are three shot groups.
1. Action open, 3 rounds in chamber, depress the varying button.

2. Second round is loaded automatically after firing the first.
3. Third round is loaded automatically after firing the second and the action locks back as mag is empty.

Welcome aboard OM.

Slowing down the round strip and chamber speed may help with autoloaders but chasing problems like this can drive one batty because the problem can also be influenced by neck tension. The factory rounds are not necessarily a reliable control group where neck tension is concerned. Taper crimps can be tricky, finding the right degree of crimp. If you have a reliable caliper or better yet, a good mic, increase your taper crimp a few thousandths. Its amazing how far down you can go and still achieve a reliable "thunk".

Hoot

First what brand of barrel ? Second what is the position of the gas tube rifle length or pistol length ?

I have never found a problem with buffer weight and a gun not functioning properly in 450 BM....have found where the hole for buffer is not in the right position or to small !

First thing I would do is strip the gun down and make sure it's properly assembled and barrel is torqued properly ! Then shoot to see if anything has changed....