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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.

Has this occurrence ever happened to anyone else? I can try and provide pictures but it's pretty difficult to see.
 
Hmmm, strange. Try a different brand of magazine? Interested in other's responses here......
 
You could have an out of spec or wrong bolt catch. I'd first try a different magazine, and then switch out to a Aero/different brand bolt catch if the problem persisted. Can you see where exactly the unwanted contact is happening? A white sharpy is a great way to find where the contact it. It might just need a little hand fitting to work perfectly.
 
You could have an out of spec or wrong bolt catch. I'd first try a different magazine, and then switch out to a Aero/different brand bolt catch if the problem persisted. Can you see where exactly the unwanted contact is happening? A white sharpy is a great way to find where the contact it. It might just need a little hand fitting to work perfectly.
I've used an aero ar10 bolt catch and a V7 ar10 bolt catch. I cannot imagine both of those being wrong. They are both reputable reliable companies.
 
Here you can see the bolt initially caught on the lip of the mag. Upon pulling back harder the bolt becomes hung up on the bolt catch, and the following images show the tooling damage common to the BCG looking from inside the magwell.

I think I'm just gonna buy an M5e1 lower with the hopes the problem is solved.

19D96725-F41E-476C-930E-349FCB49B8CF.jpeg 6299013D-50B1-492F-98B5-1442E3FCD87D.jpeg AD9B3152-10DD-47C7-AD73-B027849C6C5E.jpeg DAFFD712-D2FC-4DB7-992C-DECD231C1B66.jpeg 78946FCE-C6CA-4321-9ED8-FF6ED3A5FB24.jpeg 1A853730-E15B-4F10-85B4-9B7B8118E7B1.jpeg
 
Have you tried swapping BCG's with your buddy's gun?

It would at least rule that out.

Or even try swapping the whole upper to narrow down if it's the upper or lower.


Sounds like an ideal situation if you have access to the exact same rifle owned by a friend.
 
Is it catching without a magazine in it?. is the spring missing on your bolt catch, or maybe too weak a spring?
Have you tried swapping BCG's with your buddy's gun?

It would at least rule that out.

Or even try swapping the whole upper to narrow down if it's the upper or lower.


Sounds like an ideal situation if you have access to the exact same rifle owned by a friend.
Idk why I have not done this yet. That needs to be done ASAP.
 
Oil it...This is an AR and AR's like to run wet. That BCG looks very dry as does that entire gun. wetter is better ;)

oil up the mag catch and make sure it moves freely but springs back as it should.

on your mags make sure the followers are springing up as they should and not sticking or jamming up.

make sure the magazine fully locks into place.

Also what brand and generation is your upper receiver, lower receiver, and bolt carrier?

By generation I mean is it DPMS gen1 or DPMS gen2?

From the Magpul website regarding the PMAG LR/SR Gen M3 magazines.
*NOTE: Compatible with older model Bushmaster .308 ORC, Remington R-25, and DPMS LR308 rifles, but not optimized for bolt lock functionality with newer models based on the DPMS GII design. NOT compatible with Armalite AR-10B, Springfield Armory M1A, Rock River Arms LAR8, FN SCAR 17S, PTR-91, HK417 or any other rifles that utilize M14, FN FAL, or HK 91/G3 patterned magazines.

To accommodate longer than SAAMI-spec match ammunition, this magazine may not drop free from all makes of lower receivers.
 
Oil it...This is an AR and AR's like to run wet. That BCG looks very dry as does that entire gun. wetter is better ;)

oil up the mag catch and make sure it moves freely but springs back as it should.

on your mags make sure the followers are springing up as they should and not sticking or jamming up.

make sure the magazine fully locks into place.

Also what brand and generation is your upper receiver, lower receiver, and bolt carrier?

By generation I mean is it DPMS gen1 or DPMS gen2?

From the Magpul website regarding the PMAG LR/SR Gen M3 magazines.
This issue occurs even when drenched in oil
 
Did you ever figure out a solution? Mine is doing the same thing, hanging up on the empty mag. It doesn't get all the way back to the bolt catch, it hangs up and locks on mag in the backwards motion and stays there.It dkea this with multiple uppers. If the mag is not inserted, the bolt catches on the bolt catch just fine. When firing, the bolt comes down on top of many of the rounds, putting a dent in the cartridge.
 
I'm no expert but this was happening to a friend and it ended up being a feed ramp issue. Hogged it out a bit and polished it and it ran fine - and this was after numerous trips back to the smith that built it.

Take it FWIW and find yourself an experienced AR 10 smith cuz it isn't the same beast as the AR 15's.
 
So you can look up a previous thread I had started maybe even after this one (this thread is pretty old now) but my issue was my lower. I was using a m5e1 upper as well with a toolcraft BCG.
The issue with my lower was kinda the opposite as yours (I suspect) my issue was that the mag catch/release was milled out to low/far away to raise the magazine up to the proper height and would fail to feed. I had to solder on a stainless tab of 16 gauge sheet metal to raise the mag to proper height to feed correctly.
I suspect that your issue may be that the mag catch/release is up too high causing your magazine to impede on the bolt catch and causing excess friction on the BCG as it travels because with any mag it can never fully return to its fully "arms inside the ride till complete stop" position.

I'll try and find that thread. In that thread there were some mighty helpful folks who sent in a BUTTLOAD of AR/10 AR308 dim.'s and that really helped me troubleshoot it. Once I fixed that it ran like a champ.

This seems to be a somewhat common issue with these lowers.
 
Not sure which if any work yet, but here's some measurements:
Noreen DPMS: 0.659 and 0.256
Tactical Machining DPMS: 0.667 and 0.267
5D DPMS: 0.651 and 0.260
80lowers DPMS: 0.660 and 0.252
80lowers SR-25/AR-10A: 0.660 and 0.252

My 5D is similar to everything else, so the 0.695 might be a machining error on that lower and not a deliberate design intention. As far as I know the magazines for the original military Armalite AR-10, current Armalite AR-10A, SR-25, and DPMS LR-308 are intended to be the same, they're just usually called "DPMS" because that's probably the most common standard at the moment.
Here ya go. If yours is off on this dimension that's your culprit. Swapping all the components in the world won't work unless you figure out a way to lower that mag catch itself. That will probably be trickier than raising it in my case. But ya never know, could just be simply grinding the catch lower.
And it's really only the little tab that sticks out from the "armature" that needs lowering.

Here's the whole thread for reference:
 

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