AR short stroking, won't lock back

[Onagoth]

Can't figure this one out.

 

I recently built an 18" rifle with a rifle length gas system and a rifle (Magpul MOE) stock.

 

It did have an Aero adjustable gas block on it and I've had problems ever since day 1.  Some failures to cycle but it would always fail to lock back on an empty mag.  Never got it running very well so I put a normal gas block on it and it cycles fine now, but still won't lock back on an empty mag.  I can manually lock back the rifle on an empty mag but full power ammo doesn't seem to get it there.  It's also got a JP rifle buffer spring,  Aero rifle buffer tube.  Aero nitride BCG

 

Any ideas what the problem is?  There is no apparent binding but it's not exactly buttery smooth either.   I've built a couple 18" guns and never had this problem

 

Appreciate any help

[Dirty_J]

Gas block aligned properly? Barrel dimpled for the block? 
 

Fairly uncommon to have an under-sized gas port… I’d be looking at alignment. 

[stick]

Have you tried as different buffer spring?  

[Onagoth]

5 hours ago, Dirty_J said:

Gas block aligned properly? Barrel dimpled for the block? 
 

Fairly uncommon to have an under-sized gas port… I’d be looking at alignment. 

 

Yes...I can confirm the gas block was perfectly aligned.

 

4 hours ago, stick said:

Have you tried as different buffer spring?  

 

Tried 2 springs.  JP and one other

Edited June 4, 2023 by Onagoth

[Onagoth]

Is it possible the rifle buffer has too much weight to it?

[Dirty_J]

What barrel? What’s the port size? 

[NOSHMJ]

try an adjustable weight buffer, with adjustable gas block?  I had the same issue, had the gas port opened all the way, but ended up needing a weighted buffer on top of adjustable gas.   

[Onagoth]

3 hours ago, Dirty_J said:

What barrel? What’s the port size? 

Faxon match series 18” 

 

not sure the port size though.  

[Alaskapopo]

12 hours ago, Onagoth said:

Can't figure this one out.

 

I recently built an 18" rifle with a rifle length gas system and a rifle (Magpul MOE) stock.

 

It did have an Aero adjustable gas block on it and I've had problems ever since day 1.  Some failures to cycle but it would always fail to lock back on an empty mag.  Never got it running very well so I put a normal gas block on it and it cycles fine now, but still won't lock back on an empty mag.  I can manually lock back the rifle on an empty mag but full power ammo doesn't seem to get it there.  It's also got a JP rifle buffer spring,  Aero rifle buffer tube.  Aero nitride BCG

 

Any ideas what the problem is?  There is no apparent binding but it's not exactly buttery smooth either.   I've built a couple 18" guns and never had this problem

 

Appreciate any help

Need a JP light weight rifle buffer 

[dwbethue]

I'm running my White Oak 18" rifle length with a H2 carbine buffer and I've had no problems with it operating or locking back. You might give that a try if you have access to one (or any carbine sized buffer).

 

That's odd if you're run a similar combo on other 18" rifles without issue. 

 

Is the buffer damaged by chance? I had one rifle that went from super smooth to gritty and the cause was the roll pin in the buffer working itself loose and creating extra drag in the buffer tube.

[Onagoth]

3 hours ago, dwbethue said:

I'm running my White Oak 18" rifle length with a H2 carbine buffer and I've had no problems with it operating or locking back. You might give that a try if you have access to one (or any carbine sized buffer).

 

That's odd if you're run a similar combo on other 18" rifles without issue. 

 

Is the buffer damaged by chance? I had one rifle that went from super smooth to gritty and the cause was the roll pin in the buffer working itself loose and creating extra drag in the buffer tube.

I don’t think so.  Everything is pretty much brand new and nothing obvious stands out

 

i think I will try to remove weight from the buffer I have and try again.  if no joy, then maybe a carbine or adjustable buffer.

 

id rather not use a low mass BCG for this particular rifle….although I do like the JP one for my competition rifles

 

at this point, I’m inclined to think the gas port on the barrel is insufficient for the BCG and recoil buffer I have….which is odd because everything is fairly standard.  I will report back if I have any luck

 

thanks again all

Edited June 5, 2023 by Onagoth

[mmc45414]

I would try a different BCG, at least as a test.  A BCG bought as a component has never been test fired, I had an Aero that was flawed from birth.

[stick]

1 hour ago, mmc45414 said:

I would try a different BCG, at least as a test.  A BCG bought as a component has never been test fired, I had an Aero that was flawed from birth.

Good idea.  I would swap piece by piece until you determine the cause. Right now, we are all grabbing at straws.

[Amra86]

I had a Faxon 18 inch rifle length barrel. I had to open up the gas port to get it to run right. The gas port in the barrel was too small. Faxon gas ports are on the small side in my experience.

[Onagoth]

4 hours ago, mmc45414 said:

I would try a different BCG, at least as a test.  A BCG bought as a component has never been test fired, I had an Aero that was flawed from birth.

How do you mean?

 

The mass is off?  Or the dimensions?
 

I noticed it’s not butter smooth in the upper receiver (when charging) but I did not think too much of it

[mmc45414]

7 hours ago, Onagoth said:

The mass is off?  Or the dimensions?

I am more thinking the plumbing.

You have confirmed the gas block is aligned, have you taken the bolt out of the carrier and eyeballed it?

Maybe while it is out blow an air hose through the carrier key to see if anything is restricted?

Just is my opinion that if 50,000PSI is not enough to blow it open the plumbing is the first thing that gets my scrutiny.  Much focus on the carrier key and everyone always makes sure it is staked, but it wouldn't have to leak much to do what the rifle is doing.  Maybe with the bolt in blow air into the carrier key and listen to see if any air is leaking anywhere, especially at the carrier key.  Maybe squirt some Windex on it like a leaky tire and look for bubbles.  Somebody coulda staked the dickens out of it but if they didn't get it tight enough before they did it might do what it is.

 

BTW, I got a rifle (pictured) with a rifle length gas system and a rifle buffer and tube, with the same MOE stock, and it shoots sweet.  I actually had it out of the safe a few minutes ago, I have some upgrades planned for it.

 

 

9 hours ago, stick said:

Good idea.  I would swap piece by piece until you determine the cause. Right now, we are all grabbing at straws.

Agreed, and the BCG would be the first straw I would grab! 

 

I just think when we buy assembled things like uppers and BCGs we have to acknowledge that a person that isn't a gun nut has a job assembling it, and it gets packaged without any test firing.  The BCG I mentioned had an extractor that was incompletely machined, no big deal that a tool probably broke during a high-speed run of parts and a bad one didn't get found.  But then somebody that doesn't know what an extractor does assembled it into a bolt, and it was an obvious flaw.  Then that bolt got put into a carrier by somebody else that didn't notice it, and then Mr. Oblivious here (am looking in the mirror) put it in a rifle without noticing it.  Just sure am glad I tried to cycle a couple of dummy rounds before schlepping it all the way down to the range 

 

But yeah, IMO the things are a marvel the way they function, but really not all that complex.  But most of the complexity is in the BCG, so it is where I would start.  Actually, the first place I would start would be the gas block alignment, but that has been confirmed.  After that I would try it on top of another lower.

 

ETA: I just had another thought, is the bolt catch free and smooth and sprung properly?  Maybe you can lock it back manually, but it is moving too slow when being fired?  I think I can remember needing to twist a drill bit in the hole by hand to clear a burr that was not letting the plunger move on one?

Edited June 6, 2023 by mmc45414
grammar

[Onagoth]

Just as an update

 

i disassembled the buffer and removed one weight bringing it down to 4.5 oz

 

functions perfectly now.

 

I also bought an adjustable buffer and second BCG just in case, but didn’t need them.  I will have to build another rifle to be sure they get used
 

thanks for the help.  I May end up putting the adjustable gas block back in but not sure just yet.  Want to shoot a few matches first

Edited June 26, 2023 by Onagoth

[NoKimberDave]

On 6/26/2023 at 4:17 PM, Onagoth said:

Just as an update

 

i disassembled the buffer and removed one weight bringing it down to 4.5 oz

 

functions perfectly now.

 

I also bought an adjustable buffer and second BCG just in case, but didn’t need them.  I will have to build another rifle to be sure they get used
 

thanks for the help.  I May end up putting the adjustable gas block back in but not sure just yet.  Want to shoot a few matches first

 

Late to the party. Glad you got it running.

I had an 18" faxon gunner barrel. Although I was using a -10% spring and lo mass buffer, as well as LW BCG, I was surprised to find the gas block was only like one click down from full open.

But it ran great, and was super soft shooting and very light/pointy. Was a pleasure to shoot.

Did you do any accuracy testing on the faxon?