I got an upper from a guy on MeWe. It has an Aero upper and an 18" Stainless HBar in .223 Wylde.  He said be only put 40 rounds through it and it ran flawlessly for him!  The upper did not come with BCG so I got a new stainless BCG from PSA.

I have since made 5 trips to the range and can't get it to stop short stroking. I have the upper on a carbine lower.

I have tried the following,

Tried another lower, another BCG, got a brand new gas block and new rifle length gas tube.  Also tried other mags and ammo. All ammo was NATO spec 5.56 55 grain FMJ.  I am at a loss now!

The photo below is it failing to eject the spent round. at times it will eject but never strip off a new round.

buffer spring and weight. 

Try a new BCG from a rifle you know works and put the new BCG in a rifle that you know works.

13 minutes ago, High Exposure said:

Try a new BCG from a rifle you know works.

I was praying you would chime in!  I did try another lower from a known working carbine. Same effect!  I do have an A2 clone and I will try that one with the rifle length tube and buffer.  I always thought an 18" barrel with a rifle length gas tube should work with a carbine lower.

Both lowers worked exactly the same, no change in the short stroking.

I did try a known good BCG as well with no change. I checked the cuts on the rings of both bolts and both were properly staggered.

16 minutes ago, JohnnyB said:

I was praying you would chime in!  I did try another lower from a known working carbine. Same effect!  I do have an A2 clone and I will try that one with the rifle length tube and buffer.  I always thought an 18" barrel with a rifle length gas tube should work with a carbine lower.

Both lowers worked exactly the same, no change in the short stroking.

I did try a known good BCG as well with no change. I checked the cuts on the rings of both bolts and both were properly staggered.

What kind of gas block?  Adjustable or fixed?  Is it on there properly?

Does it cycle ANY rounds or short strokes every round?

What kind of ammo?

And have you tried the upper on a known working lower with a known working BCG?

How is the barrel cut?  How does the brass look?  Possible the chamber was cut poorly and holding up the brass?

Does the gun fully cycle when you manually rack the bolt and then extract it?

 

I suspect the dwell time of the rifle length gas system is too fast and not pushing enough gas pressure to effectively cycle the action

Gas block is YHM fixed. Absolutely installed properly. It never cycles a round and Federal American Eagle 5.56 and PMC NATO surplus 5.56. all 55 grain.

1 minute ago, JohnnyB said:

Gas block is YHM fixed. Absolutely installed properly. It never cycles a round and Federal American Eagle 5.56 and PMC NATO surplus 5.56. all 55 grain.

Try 223 ammo instead?

And whose barrel is it?  Sure it is 223 wylde and not another variant?

And the does it rack and extract fine otherwise?  

6 minutes ago, Maksim said:

And have you tried the upper on a known working lower with a known working BCG? Yes

How is the barrel cut?  How does the brass look?  Possible the chamber was cut poorly and holding up the brass? Brass looks fine

Does the gun fully cycle when you manually rack the bolt and then extract it? Yes

The barrel is stamped .223 Wylde.

 

Quote

 

Here is a link to what the barrel looks like. right down to the lettering.https://sandersarmoryusa.com/product/18-hbar-stainless-steel-rifle-length-w18-twist-223-wylde-and-5-56-nato/

Two things I would check:

1) carbon build up in the gas block?

Plug the back end of the chamber, and Use an Air Gun to blow air into the barrel from the muzzle end. This should route the air through the  gas block port and blow any debris back through the gas tube.

2) Remove gas block and see if the hole (port) in the barrel is properly drilled, and there are no burrs blocking the gas port. Also check for proper alignment between the hole in the barrel & the hole in the gas block.

 

2 hours ago, Maksim said:

Try 223 ammo instead?

And whose barrel is it?  Sure it is 223 wylde and not another variant?

And the does it rack and extract fine otherwise?  

If the rifle is Short Stroking, it's not getting the proper amount of pressure to blow the BCG back far enough to allow the proper timing for ejection. Going from 5.56 to .223 would just reduce the amount of gas (pressure) and make it worse imo.

The cal. of the barrel should no impeed the stroke

8 minutes ago, JT Custom Guns said:

2) Remove gas block and see if the hole (port) in the barrel is properly drilled, and there are no burrs blocking the gas port.

This too.  I've read many a post about out of spec gas ports.  It does not happen often, but often enough that it comes up every now and then.

#1, eh, not so much.  15K+ PSI is a pretty good pipe cleaner.

27 minutes ago, Scorpio64 said:

This too.  I've read many a post about out of spec gas ports.  It does not happen often, but often enough that it comes up every now and then.

#1, eh, not so much.  15K+ PSI is a pretty good pipe cleaner.

I've seen people clean the gas tube by spraying cleaner in it and using a pipe cleaner, but this tends to push the carbon sludge into the gas port. When trying to solve a problem, it's best to go through all possibilities because it's usually the one you miss in the first place....... jmo

@JT Custom Guns

It's a brand new gas block and tube. It is absolutely tight and lined up exactly with the port on the barrel. 

Let me clear up what scorpio is trying to tell ya. 

Da hole in duh middle of barrel is fukdup

Do me a favor take a rough measurement from the gas block to the end of the threads for the brake. I don't feel like clicking your link. 

 

18 minutes ago, JT Custom Guns said:

clean the gas tube by spraying cleaner in it and using a pipe cleaner, but this tends to push the carbon sludge into the gas port.

How many rounds before a gas port, block or tube gets gacked with carbon buildup... 100, 1000, 5000?  The upper has, if all accounts are true, less than 100 rounds through it.  If there is buildup, spraying cleaner is more likely to clog the system, instead of blowing anything out.  I've read more posts about people screwing up their rig trying to clean the gas system than I have about folks correcting it.

Whatever the problem is with the upper, it is compounded by using a carbine lower with a rifle upper.  A new gas tube and an inspection with gas port gauges is in order.

I didn't say to clean the tube, you only quoted a portion of what I said..............

19 minutes ago, Scorpio64 said:

How many rounds before a gas port, block or tube gets gacked with carbon buildup... 100, 1000, 5000?  The upper has, if all accounts are true, less than 100 rounds through it.  If there is buildup, spraying cleaner is more likely to clog the system, instead of blowing anything out.  I've read more posts about people screwing up their rig trying to clean the gas system than I have about folks correcting it.

Whatever the problem is with the upper, it is compounded by using a carbine lower with a rifle upper.  A new gas tube and an inspection with gas port gauges is in order.

As per the OP, he already replaced the gas block and a tube.  Leading to improperly done hole...

Humn, got access to a bore scope?

My first thoughts were screwed up chamber causing issues with extraction but more and more agreeing with @Scorpio64 that someone botched the barrel job.

And btw, for new folks... THIS IS WHY YOU TEST FIRE ANYTHING YOU BUY USED!  But I have yet to see a barrel from a quality producer have issues... and well.. whoever sold it to you saying 40 rounds with "no problems" likely lied.  

 

For @louu The hole in da middle is .0938 and very clean. It is exactly where it should be for the rifle length gas tube and block.

Thank you for asking! I appreciate the help from such experienced experts such as yourself and many others here!

Johnny, how are you insuring the gas block hole and gas port are aligned at installation?

22 minutes ago, Shane45 said:

Johnny, how are you insuring the gas block hole and gas port are aligned at installation?

I measured and marked the block and barrel then to verify, I connected .17" vinyl tube to the receiver end and blew air through the tube while holding the end of the barrel tip up to my ear while moving the block very slightly, stopping at the highest airflow.

While unconventional, the method is fool proof.  Logically speaking...It can't fail!

It was amazing how much a very slight movement of the block had a great effect on the air flow! I realized I could get pin point accuracy using this incredibly simple method! Wait! Did I just invent this or is this how everyone does it? It was the most logical method I could think of!

Indeed it is amazing how a tiny bit off impacts it. Leaves me scratching my head a bit. 

1 minute ago, Shane45 said:

Indeed it is amazing how a tiny bit off impacts it. Leaves me scratching my head a bit. 

I will try the upper with a known good lower setup with a rifle length buffer setup and report back!

At the end of the day, there is only one reason... "You're limp wristing it."

Really weird... 

This is what I use for dimpling and aligning a gas block.

 

https://www.wingtactical.com/accessories/gear-tools/gun-tools/slr-rifleworks-ar-gas-block-dimple-jig/

Any chance you’ve got an issue in the BCG?  Loose gas key? Occlusion in the gas key?  Does the bolt itself rotate and extend smoothly?  Gas rings on the bolt intact?:

30 minutes ago, DirtyDigz said:

Any chance you’ve got an issue in the BCG?  Loose gas key? Occlusion in the gas key?  Does the bolt itself rotate and extend smoothly?  Gas rings on the bolt intact?:

I tried using a known good BCG and same effect. I put a rifle lower on it and just have to get back to the range to test it.