AR pistol 7.5" problem.

[biggie24420]

Hello everyone,
I looked on NWFA and didn't find anyone who had the issue I am having so I wanted to start this and see if you guys can help me out...

This is my problem:
I have put probably 250 rounds through it and most have been .223 but I have shot probably 40 or so rounds of 5.56. My problem is that my BCG does not lock back after shooting the last round. With all the rounds I put through the firearm, it has locked back twice from what I can remember. If I push down on the bolt catch as if I wanted to lock the bolt back manually with the charging handle (on the normal side, left side of the receiver) the bolt will lock back after shooting the last round and I can still pull the BCG back and have a gap (1/8th inch or so) between the bolt face and the part of the bolt release that makes contact with the bolt to hold it back.

I am able to manually lock the BCG back and if I put an empty mag in and pull on the charging handle, the bolt will lock back and stay locked as it should.

I have used one Lance 30 round mag, one old Colt GI 30 round mag, and an okay industries 20 round mag. Both the OKAY and Lance mags are pretty new and no damage to either mag. They all feed good and work well with my Spikes M4.

My brass, depending on what buffer I use, it can be from 1 o'clock to 3 o'clock and from what I have researched, I am over gassed? I did not see anything weird with my brass either...

Parts I have:
-Upper: redXarms 7.5" upper DI ( I posted a pic of the info about the upper)

-Lower: Aero Precision lower with a PDQ ambi-bolt release already installed when I got it from Primary Arms.

-Bolt: Sharps reliabolt

-Bolt carrier: Whatever came with the Stag Arms M4 I had, looks like the M16 bolt carrier. I still have the original bolt too but running the sharps instead. I've ran the same bolt in my M4 and no issues.

-Brace: SB Tactical PDW brace with three positions. On the box it tells you it is "compatable with mil-spec bolt carrier groups and carbine buffers".

I have a carbine buffer spring (37 coils) and a non marked buffer that came off of a Stag M4. I also have a Colt carbine buffer spring (37 coils) and a wolff extra power buffer spring 16501, to be used in "colt car15 & M4, .223 Colt SMG, 9mm.

I have also used a Spikes tactical H2 and a Colt H3 buffer and still no bolt lock back on last round. I have not had a single FTF or FTE. It has been reliable and good..... only problem I have is the pesky BCG not locking back after shooting the last round. To be clear, I have used three buffers, unmarked and light weight, H2, and H3.

I did run my spikes M4 upper on the Aero lower and I had the same issue. I thought that maybe my ambi-bolt release was being held down by the dust cover, not allowing the mag follower to push the bolt hold open up to lock the BCG back.....and that was one of the reasons why I cut off a portion of the dust cover. So needless to say I am all kinds of confused. My M4, when shot as is, it has no issues, so I don't know why the M4 upper (BCG) didn't lock back on the Aero lower.

So I think I need to get an adjustable gas block..... what do you guys think?
I live in Beaverton, any good gunsmiths you guys recommend?



Thanks for your help boys and girls... I appreciate it.


This is the barrel my pistol came with.

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[308]

What happens when you put the stock bolt catch back in?

 

[biggie24420]

I don't have the stock one. I bought the new "blem" lower and it had the fancy bolt catch already installed. And it moves up and down freely... I don't feel any dragging or rubbing. It's so weird...

 

[Kruel J]

Have you checked the gas block to make sure its tight and aligned properly? Almost sounds like its under gassed just a bit and is short stroking.

 

[dmack]

If you had the same problem with two different uppers on the same lower, it sounds like the lower. My guess is an out of spec bolt catch,. Could be an out of spec lower, but I haven't heard of any issues with Aero precision. I would try to find a standard spec bolt catch to try.

 

[biggie24420]

Have you checked the gas block to make sure its tight and aligned properly? Almost sounds like its under gassed just a bit and is short stroking.

It looks like it's on there good and tight. It's not canted or sticking forward.

 

[MasterChief]

Type of ammo?

 

[biggie24420]

If you had the same problem with two different uppers on the same lower, it sounds like the lower. My guess is an out of spec bolt catch,. Could be an out of spec lower, but I haven't heard of any issues with Aero precision. I would try to find a standard spec bolt catch to try.

Ya I think that's the cheapest option I have for now. I mean I am glad that this is the only problem I have. I'd be sad if I had feeding or ejecting issues.

 

[biggie24420]

Type of ammo?

I've ran brass only. Just over the counter stuff. IMI, Federal, PPU, Blazer Brass, Wolf gold, Armscore. I do remember shooting some green tips too.

 

[old11bravo]

I agree with the earlier assessment that it sounds slightly under-gassed. An adjustable gas block will not do you any good for under-gassed rifles, they are for rifles that are over-gassed.

I would check and make sure the gas key on your BCG is aligning and sealing on the gas tube each time it cycles. There will always be a little bit of gas escaping around where the gas block is mated to the barrel but look for any signs of excessive leakage. Check the gas system for any blockages that could be inhibiting the gas flow. Blow air through the gas block and tube to make sure it's clear. Last of all, if you remove the gas block you can check the alignment of the port in the gas block to that of the port in the barrel. If the gas port holes are misaligned, there will be tell tale marks and you can fit the gas block for better alignment.

Hope this helps. Good luck and update us with any new findings.

 

[biggie24420]

I agree with the earlier assessment that it sounds slightly under-gassed. An adjustable gas block will not do you any good for under-gassed rifles, they are for rifles that are over-gassed.

I would check and make sure the gas key on your BCG is aligning and sealing on the gas tube each time it cycles. There will always be a little bit of gas escaping around where the gas block is mated to the barrel but look for any signs of excessive leakage. Check the gas system for any blockages that could be inhibiting the gas flow. Blow air through the gas block and tube to make sure it's clear. Last of all, if you remove the gas block you can check the alignment of the port in the gas block to that of the port in the barrel. If the gas port holes are misaligned, there will be tell tale marks and you can fit the gas block for better alignment.

Hope this helps. Good luck and update us with any new findings.

Well I've done the oil on gas key checking for air bubbles. The sides of the key are not leaking but in front of the key, right under the gas key where the gas tube fits into or slips into the key (orange circled area in the pic), I have seen air bubbles when testing.

I have checked my spikes tactical bolt carrier and same thing with that gas key. But I think that's normal and it's the sides of the gas key that's important, if it leaks from that area. But someone correct me if I am wrong.

The gas block isn't showing any leaks from anywhere and is on the barrel nice and tight. It also looks straight and not canted or sticking forward..... it's resting nice and tight against the shoulder I guess you'd call it.

Since the pistol feeds and ejects just fine, I'm not too worried but eventually I want the BCG to lock back as it should after the last round.

Yeah I will definitely keep everyone up to date with this issue.

 

[old11bravo]

Try running your Spikes BCG in the trouble rifle. I once had a lightened BCG with issues similar to your description. Maybe a heavier BCG will have enough inertia to lock back on the empty mag.

 

[Stomper]

It could also be the extra weight of the ambi-release hanging off the right side of the receiver (since the pivot-pin is on the left side of the receiver) causing just enough resistance so it won't engage fast enough when cycling.

 

[Garg]

If you have tried two different uppers, and the problem persists, I would say the problem is the lower. A standard bolt catch is what I would try first.

 

[308]

If you have tried two different uppers, and the problem persists, I would say the problem is the lower. A standard bolt catch is what I would try first.

Pretty much narrows it down to one common denominator

 

[biggie24420]

Try running your Spikes BCG in the trouble rifle. I once had a lightened BCG with issues similar to your description. Maybe a heavier BCG will have enough inertia to lock back on the empty mag.

I've tried using the spikes BCG but same problem.... doesn't lock back after last round.

 

[biggie24420]

I'm gonna buy a Colt bolt latch and go from there.

 

[biggie24420]

I did some more research and found someone who bought the same lower as mine and had some issues like I'm having. It's looking more and more like the PDQ ambi bolt release is the problem. The Colt bolt hold open lever has been ordered. I'll have the part installed just in time for my visit to the range next month.

 

[Velzey]

As of late I've found the bolt catch location .015 to high on a blem lower. On the same rifle I found a bolt carrier that was .025 thick on the bottom, but still in spec. This combo was just enough to have a short stroke problem.
The interference was just enough to slow the action down and cause short stroking.
I was able to work around the problem by putting an adjustable gas block and give that sucker more fuel to work the action.

But it bothered me that I had to do that so I spent hours measuring and seeing what he hell was actually worn with this one.

I assume you built/assembled this pistol?

 

[biggie24420]

As of late I've found the bolt catch location .015 to high on a blem lower. On the same rifle I found a bolt carrier that was .025 thick on the bottom, but still in spec. This combo was just enough to have a short stroke problem.
The interference was just enough to slow the action down and cause short stroking.
I was able to work around the problem by putting an adjustable gas block and give that sucker more fuel to work the action.

But it bothered me that I had to do that so I spent hours measuring and seeing what he hell was actually worn with this one.

I assume you built/assembled this pistol?

I put the internal parts inside the lower. All the lower had was the PDQ ambi-bolt catch.

The upper was a fully assembled upper without a BCG and charging handle.

If the Colt bolt hold open latch doesn't fix it I'm gonna probably take it to a gunsmith....