Ar10 bolt jamming up on PMag/mag release

[hgfty]

this is kind of hard to explain, I am also pretty experienced with the AR platform, my M5e1 upper is assembled on an 80% lower. When I rack the bolt back on an empty magazine my bolt carrier jams up as soon as the carrier reaches the mag release and mag release area of the mag. It jams extremely hard, if I mortar the charging handle I can get the bolt carrier group past the bolt catch and everything then locks back as it should. If I do not mortar the BCG all the way back and drop the mag, the bolt carrier slams forward. I do not understand why the BCG is getting hung up on that spot. I have swapped mag releases and tried a few different PMags, haven't tried any other mags yet.

 

[Hecouldgoalltheway]

Try some other mags, but you may have an issue with the upper or lower machining. Does it pass smoothly when you take the upper and lower apart? Find that out, as it may tell you which half of the rifle the problem is in.

Take the buffer and buffer spring out, does that change anything?

Is there any marring on the BCG? With the kind of required force you're talking about, I would assume there is a point on the BCG that is catching some serious contact..

 

[hlee]

80% lower, you say? Try the mag/catch and upper on a factory machined lower. Then, when they all works together as they should, 86 the diy lower.

Seriously, It could be something as simple as the mag sitting too high in the mag well. If this is the case, you can modify the mags or the catch to allow them to sit lower when inserted.

Or, you can shit can the faulty lower…

 

[msgriff]

The first thing that I would check is if the mag is riding too high due to your mis-matched upper and 80% lower.
The mag catch channel location varies between manufactures, probably even more so with an 80%. On an Aero M5, the center of the mag catch arm, measured from the top of the lower, is ~0.790".
Next thing I would look at would be an incompatible bolt catch, which again vary between manufacturers.


ETA: If you can, take a picture of the BCG through the ejection port at the point which the BCG starts to bind. Doesn't need to be a close-up picture.

 

[bfoosh006]

Large Frame AR's have a variety of bolt catch styles in use.

It may be as simple as you have the wrong style in use.... worth checking IMHO.