I just put one in, fit fine no modification needed.
But does it hold open the bolt after last round automatically. The 2 mags I have wont by hand. I have not shot it yet. But I would figure you could pull the handle back and let go and the catch would lock it open. But it only stops on the green follower.
Will work if I press the paddle while holding the bolt open.
From this video it says its a true BHO. I dont have that bolt its a all cmmg dedicated rifle, if that matters. http://www.youtube.com/watch?v=r6hd__qGDG4&feature=related
If you are doing it by hand you will have to give it a sharp pull. Be sure to watch the vid that shows proper fitting. Many times minor binding will hinder best function. We do offer a lighter weight bolt catch springs for the more stubborn rifles.
That said, you may not need to do anything. Give it a try as is.
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The bolt catch spring pressure is the biggest issue with the BHOA function.
Also, if the frame of the BHOA is tight in the upper, sand the sides of the frame for a looser fit.
it also dropped in my bushmaster and did the same thing, but I will have to shoot it to be sure
I figured it would work like a regular ar and lock back on an empty mag
Mine didn't lock on an empty mag but would work fine when used with live fire. Its all in how fast the bolt is moving back and how quickly that mag follower jumps up. Also, don't forget to carefully adjust it. The BHOA's sometimes need some "tuning". Our "mil-spec" ARs vary far more than most realize. Once you get it right however, its a nice piece.