AR15 Cycling Issues

[Hueco]

I was finally able to get my second AR build out to the range and...2 things kind of wonky.

I had to mix and match some parts, so, here were the starting builds (only pertinent parts listed)

1. Build 1: DMR
   1. 20" barrel with rifle length gas
   2. JP Captured buffer spring
   3. JP BCG
2. Build 2: Mid Length
   1. 14.5" barrel with Midlength gas
   2. A5 buffer tube with Sprinco Green, A5-H2 buffer
   3. Aero BCG

Wonky #1: Failure to Feed, Failure to fully lock the bolt back

Shooting the Middy, the rifle would not cycle. The BCG would not reciprocate far enough back to pick up another round. Occasionally, it would move far enough back to get stopped by the bolt catch (on a last round) but not far enough back...loading another mag and releasing the bolt would cause the BCG to just skip over the round. It looks like the bolt itself was sticking over top of the round while the bolt was locked. Using the charging handle to yank the BCG back all the way fed correctly.​

​

I switched to my other lower, using the Middy with the JP Captured spring and had zero cycling issues.​

​

This leads me to believe that my Middy needs an A5-H buffer instead of the A5-H2...no?​

Wonky #2: JP BCG failure to close

After deducing that both uppers cycled on the JP Spring, I went to sighting them in. I almost immediately started getting, what I thought, were light strikes. Turns out, the BCG was not fully locking into battery. What do you know, I actually got to use the forward assist! But really - this was a consistent problem.​

​

And it was a problem for both uppers. I swapped out to the Aero BCG and had no issues with either upper.​

​

I'm completely lost on how to explain this one...? ​

I ran both rifles dry, wet, and in between and the two wonkies above were consistent. When running, brass ejected into a damn near perfect little pile between 3:00 and 4:00 o' clock.

What do you think?

Read More

 

[Member 34319]

Both were never fired?

Why not start with lighter buffers? I don't start with heavier buffers, always carbine. Then I go one heavier until it won't cycle, step back one weight, double test and keep it if it is solid.

Id say both issues where likely short strokes. Likely both due to heavy recoil set ups.

 

[TTSX]

What ammo is being used? I have a couple rifles that work on NATO spec only, anything less and short strokes aplenty. Also, how sure are you your gas ports are aligned?

 

[P7M13]

After deducing that both uppers cycled on the JP Spring, I went to sighting them in. I almost immediately started getting, what I thought, were light strikes. Turns out, the BCG was not fully locking into battery. What do you know, I actually got to use the forward assist! But really - this was a consistent problem.

This is likely a headspace issue that I have recently wrestled with on my new AR10 build.
Do you reload - and if you do, do you have small base dies?
The cases can be measured to see/confirm. You can also have your head space checked at ORW as a courtesy.

 

[Ops]

lowers? gas blocks? reloads? factory loads?

blow through the gas tubes?

incorrect buffer weights, not enough gas. correctly installed barrels?

 

[Cerberus Group]

Is the JP BCG a lightweight competition design?

 

[Hueco]

Both were never fired?

Why not start with lighter buffers? I don't start with heavier buffers, always carbine. Then I go one heavier until it won't cycle, step back one weight, double test and keep it if it is solid.

Id say both issues where likely short strokes. Likely both due to heavy recoil set ups.

Why not start lighter? Because that would make sense and take away the joy of guessing and being right...at the cost of guessing and being wrong .The 20" was previously fired and had suffered the BCG issue (not going fully into battery). I hadn't gotten around to diagnosing that one until this last trip.

Any thoughts on why the JP BCG would short stroke while the Aero wouldn't?

What ammo is being used? I have a couple rifles that work on NATO spec only, anything less and short strokes aplenty. Also, how sure are you your gas ports are aligned?

Winchester M193. Decently sure the gas ports are aligned.

This is likely a headspace issue that I have recently wrestled with on my new AR10 build.
Do you reload - and if you do, do you have small base dies?
The cases can be measured to see/confirm. You can also have your head space checked at ORW as a courtesy.

I'm just getting into reloading and haven't for these, yet. Ammo was Win M193, factory fresh. I've got go and no go gauges that I used to check both bolts. As an additional point, the 20" is a Krieger barrel and I bought the exact bolt they used to check headspace after cutting the chamber.

lowers? gas blocks? reloads? factory loads?

blow through the gas tubes?

incorrect buffer weights, not enough gas. correctly installed barrels?

DMR lower is Seekins, Middy is Aero.
DMR barrel is Krieger using a YHM gas block, Middy is Ballistic Advantage for barrel and block.

Factory Win M193 ammo.

Blow the tube? Gettin' a little personal there, aren't we?

Is the JP BCG a lightweight competition design?

No. Regular Full Mass Operating System (FMOS) BCG.

 

[American123]

If it's not locking the bolt catch on an empty mag that is generally always a low gas issue or a too heavy of buffer/spring issue. Assuming your BCG isn't gummed up like paste.

Let's start with the easiest things first. Put a lighter buffer in it.

 

[Lasers]

I'd start with what you're already saying, change out to a lighter buffer setup and test again. I have one you can borrow in the parts bin if you need it

 

[TTSX]

Speaking of buffer weights, has anyone run a buffer with no weights at all? Like a hollow one? I'm channeling my inner arakboss tonight

 

[Cerberus Group]

With full mass BCGs running mid length gas...those two things will run an A5-H2 buffer with a green spring.

Am guessing gas issue.

When building an AR, gauge every part before assembly...it's amazing how many top rated parts and BCGs fail or are close to failing right out of the box.

 

[Ops]

jp probably weighs more than the aero. and id switch to a H , i prefer adjustable gas blocks myself

 

[arrowshooter]

Speaking of buffer weights, has anyone run a buffer with no weights at all? Like a hollow one? I'm channeling my inner arakboss tonight

I have/do. I have an 18" .223 that would not pickup the next round or lock back until I emptied the buffer, then it ran just barely making the 4:30 ejection. I have since taken the gas port up two steps and now it runs fine with a heavier buffer.

I also have a 16" 300 BLK that was pushing the brass to about 5:00 but ran. I put an empty buffer in that one just to insure I would not have any reliability issues.

I will say that the .223 was a very soft shooter, I mean 22LR soft, until I opened up the gas port which in turn brought on more muzzle rise and recoil. I bought one of those Oden Works (I think) adjustable buffers, which was fun to tinker with and solved everything.

 

[DirectDrive]

Good advice ^^^
Start with a carbine weight buffer and bone-stock carbine spring, get it running and then swap in the boutique parts one at a time.

I would have used carbine gas on that 14.5", so you are giving up a little dwell time with mid gas.
Ammo is good for the maiden voyage (or M855)

 

[Member 34319]

Any thoughts on why the JP BCG would short stroke while the Aero wouldn't?

Maybe one weighs less. Tighter tolerance in the JP could be the culprit.

 

[orygun]

Following along for info. I am a mechanic, after all, and I like to be able to fix things.

 

[arrowshooter]

Tighter tolerance in the JP could be the culprit.

Roger this. Deserves a couple hundred hand cycles with minimal lube in front of the TV.