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Mag inserting too far?


gerritm

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Had a weird malfunction with my .223 AR over the weekend I built. Have shot this lower/upper combo many rounds without an issue, but never went prone before. Went prone with a double mag & it malfunctioned. BCG would reset enough to go click, ejected the spent case, but BCG would not close completely. Looks like the bolt catch may be getting pushed up by mag and dragging on bottom of BCG. Tested it with several different Magpul mags and could duplicate this. Mag release works fine.

 

Insert the mag & shoot offhand and it works fine, use mag as a pod and it happens.

 

Bad out of spec lower? Magwell is very tight with little play in mag when inserted. these are Magpul mags. 

 

Replace bolt catch (seems to be more play in it than my other rifles)? 

 

gerritm

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Figured this out. Wasn't the bolt catch or out of spec lower. Replaced the bolt catch and no change. Changed BCG's and no change. Replaced the buffer & spring with a slightly heavier one and problem went away. I think when you went prone mono podding off the mag put just enough drag on the bolt to slow it down slightly, enough not to completely close. 

 

gerritm

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gerritm, if your running adjustable gas and have it turned down to minimum it can also cause this but if it is running fine with a heavier buffer and spring and you did not increase the gas then it sounds like you found the problem.  The top round in the mag can rub on the bottom of the bcg and slow it down a little and it gets worse when you monopod.  I use heavy monopoding as the acid test for my adjustable gas level.

 

  Jeff

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Not running an adjustable gas block, yet. I shot well over 1K rounds thru this combo, but changed the barrel out. Never mono podded it before as I usually shoot open with a bipod. We tested it, zeroed it, and ran couple of hundred rounds before the match to make sure all was good. I guess this is one more check before taking it to a match.

 

gerritm

Edited by gerritm
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