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Discussion Starter · #1 ·
I've found that the magazine can easily override the magazine catch when doing and emergency reload. Not a great deal of force is required for this to occur. The magazine overrides the catch, and sticks in the "too high in the mag well" position. Pics attached.
 

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Discussion Starter · #2 ·
The result when this occurs is the same about 90% of the time. When the bolt is released, the magazine is thrust downward in the magazine well/lower receiver, runs past the mag catch, and falls out of the rifle. No round is chambered as a result.

Upon examining the lower receiver, it became apparent that the bolt catch does not limit the upward movement of the magazine sufficiently to prevent it from overriding the mag catch. As a comparison, the design of the AR bolt catch physically limits the upward travel of the magazine when inserted to prevent mag catch override.

The upward travel limit of the ACR bolt catch is quite generous, and the magazine can physically move farther up the magazine well/lower receiver than it should.

In addition, the mag catch spring on the ACR is rather weak, in comparison to the AR mag catch spring. With the ACR, this acerbates the issue by not "catching" the magazine on the way in, nor "catching" it on the way down when the bolt goes forward. This accounts for the magazine falling out of the rifle when the bolt is released - the mag catch spring was stronger, the magazine would likely be held in place and the top round would chamber.

I think Bushmaster should take a look at both issues, and perhaps upgrade the mag catch spring to one of greater force. The bolt catch issue might be too much to address with a redesign, but a slightly stronger spring might do the trick.

I think this rifle has great promise, as it is accurate and ergonomic in most other respects. But this magazine/bolt catch issue and the selector lever need some retooling.
 

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This happens to me sometimes when I do a reload "too fast?" with an AR one can just slam the mag in, give it a quick tug and go. On the ACR (usual when the bolt it locked back) if the mag is rammed in and tugged to check the purchase, it will often slide right out. You almost have to give it a second to catch the mag before bringing the bolt home.
 

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I've never had that problem. If anything, I have to slam in the magazine extra hard to seat it if the bolt is closed and the mag is full (30rds).
 

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For me it was the mags!

I had the same exact problem. This was with 6 Magpul magazines. When doing a reload with the bolt locked back, slamming the mag home and then tugging to insure it was locked in place always pulled it out. If I didn't tug, usually when I let the bolt go forward, the mag would drop to the ground.

Interesting thing is I was one of the early ones to have the full auto problem and they used my gun for testing when I sent it in. Since they put a lot of rounds through it, they actually gave me a brand new rifle in return. Guess what? Same exact problem.

I talked to BM and they felt it could be the mags. I purchased them all at the same time and the manufacture date was 2008. I got my hands on a GI mag and no problem. I contacted Magpul and the magazines have been through several revisions since I purchased the ones I had. They sent replacements for all of them - no more problem. I took some measurements and the older mags were slightly more narrow. This was enough for the protrusion on the magazine which stops the upward travel to slip past the catch. Since then, I have had no problem and I tried several other standard GI mags too.

So, could it be your magazines? Are they older Magpul mags? Try a GI mag and see if you have the same problem.

I have to say both Bushmaster and Magpul were great to work with. We spend a lot of time on the phone trying to figure out what was going on. Original mags were well worn and several years old - replace all with no questions asked...

Let us know what you find!
 
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