SBR cycling issues

[Diesel Kinevel]

I recently put together my 10.5" upper after getting my stamp back. While test firing it failed to feed on multiple occasions. It seems as though the bolt is not moving far enough back to strip the next round out of the mag. I tried several different mags to no avail. I checked the gas system and everything is functioning as it should.

I tried an H and an H2 buffer with a Wolff power spring. Neither solved the issue.

Any ideas?

Thanks,

Z

 

[iH8DemLibz]

It needs more gas.

I've built some guns that didn't have enough bore left in front of the barrel gas port. This did not allow for the gas to trapped in the bore long enough to be effective.

My fix was to open the gas port in the barrel a tad at a time until it cycled properly.

My theory on semi's has always been either too little gas in front or too much spring in the back.

I'm certain others will have their own opinions on the matter.

 

[Flipz]

I recently put together my 10.5" upper after getting my stamp back. While test firing it failed to feed on multiple occasions. It seems as though the bolt is not moving far enough back to strip the next round out of the mag. I tried several different mags to no avail. I checked the gas system and everything is functioning as it should.

I tried an H and an H2 buffer with a Wolff power spring. Neither solved the issue.

Any ideas?

Thanks,

Z

Who made the barrel?
What muzzle device are you using?
Have you tried a standard milspec buffer spring and carbine buffer?
What ammo have you tried?
How do you know the gas system is functioning as it should if you're having malfunctions?

 

[amoebicmagician]

where's your gas port drilled?

 

[amoebicmagician]

It needs more gas.

I've built some guns that didn't have enough bore left in front of the barrel gas port. This did not allow for the gas to trapped in the bore long enough to be effective.

My fix was to open the gas port in the barrel a tad at a time until it cycled properly.

My theory on semi's has always been either too little gas in front or too much spring in the back.

I'm certain others will have their own opinions on the matter.

Damn it, beat me to it

 

[clandestine]

Wolf Springs or XP SPrings, and H Buffers are not the answer for a short stroking/undergass issue. Use a COLT Buffer Spring (Action Spring) and a Standard Carbine Buffer.

Who made the upper? What Gas Block or FSB is installed? Do the Ramps match? What kind of ammo? Is the Hammer notched? Is the Carrier Shrouded? WHO makes the BCG? (Yes it matters a great deal)

 

[K-Romulus]

Could also be lack of lube. I had this same issue happen to my 11.5" when I tried a "new" method of using "just enough" lube instead of my usual "drown it" method.

2000 prior rounds had no problems, 200 rounds after going back to the old lube method have seen no more probs.

The only causality I can think of is that lack of lube was increasing friction and slowing things down enough to cause problems; for a few times the carrier didn't even complete it's full forward movement.


Sent from my iPhone using Tapatalk

 

[Calengor]

My centurion 10.5 MK18 would not cycle with an H2 buffer, and runs fine with an H buffer. You may need a lighter buffer than that.

The problem is not the gas system itself, but rather that you have too much resistance in the form of the extra powered springs and heavier buffers, as others mentioned.

 

[coopermania]

 

[Wayne1one]

go slow one change at a time, carbine buffer should do the trick.....

 

[JailHouseLiar]

I recently put together my 10.5" upper after getting my stamp back. While test firing it failed to feed on multiple occasions. It seems as though the bolt is not moving far enough back to strip the next round out of the mag. I tried several different mags to no avail. I checked the gas system and everything is functioning as it should.

I tried an H and an H2 buffer with a Wolff power spring. Neither solved the issue.

Any ideas?

Thanks,

Z

As other have said, try running it with a standard spring and buffer. Place one round in the mag, fire the rifle. Pay attention to the ejection pattern, 2:00, 3:00, 5:00?

Does the bolt cycle enough to lock open on the empty mag? Not enough gas and too much gas sometimes act the same way. Also some ammo is a touch underpowered.

Where are you test firing it?

For comparisson, who made the barrel or upper and what size is that gas port hole?

Answer these and we may be able to zero in on what's making it short cycle.

 

[rsideout]

WHO makes the BCG? (Yes it matters a great deal)

True. One of my SBRs had trouble cycling. I swapped the BCG with one of my other ARs and never had another problem.

 

[Diesel Kinevel]

Thanks for all the responses. Here's a run down of the parts:

Stag upper with a JoeBob BCG

Rainier arms 10.5" barrel with A2 on the front

Carbine length gas system

I did check the gas system and found it to be in line with other rifles I have that function reliably. I have yet to try a carbine buffer and standard spring. The bolt will lock open on an empty mag.


-Z

 

[coopermania]

Wolf Springs or XP SPrings, and H Buffers are not the answer for a short stroking/undergass issue. Use a COLT Buffer Spring (Action Spring) and a Standard Carbine Buffer.

Who made the upper? What Gas Block or FSB is installed? Do the Ramps match? What kind of ammo? Is the Hammer notched? Is the Carrier Shrouded? WHO makes the BCG? (Yes it matters a great deal)

Personally Diesel, I would answer all of Chads questions and listen to his advice.

 

[clandestine]

Put in a std weight colt spring and standard carbine buffer and retry. If you are using any steel cased or pmc then use something else to test. Pmc is awful in my experience.

Test gas tube alignment by removing the bolt head from the carrier and drop the carrier into the upper without a charging handle. There should be no binding when the gas key telescopes over the gas tube. If there is that's one of the problems.

If it still don't run with a buffer and spring swap then swap the bcg from a functioning gun. If that dosent work then its likely the gas port size.

What king of fcg is in the gun?

 

[clandestine]

Personally Diesel, I would answer all of Chads questions and listen to his advice.

You are too kind. Someones gonna hate on you for that

 

[CATMdude]

Wolf Springs or XP SPrings, and H Buffers are not the answer for a short stroking/undergass issue. Use a COLT Buffer Spring (Action Spring) and a Standard Carbine Buffer.

Who made the upper? What Gas Block or FSB is installed? Do the Ramps match? What kind of ammo? Is the Hammer notched? Is the Carrier Shrouded? WHO makes the BCG? (Yes it matters a great deal)

Thanks for all the responses. Here's a run down of the parts:

Stag upper with a JoeBob BCG

Rainier arms 10.5" barrel with A2 on the front

Carbine length gas system

I did check the gas system and found it to be in line with other rifles I have that function reliably. I have yet to try a carbine buffer and standard spring. The bolt will lock open on an empty mag.


-Z

I see that you are in Frederick. If you need it, I have a Colt buffer and spring that you can borrow.

 

[Diesel Kinevel]

Put in a std weight colt spring and standard carbine buffer and retry. If you are using any steel cased or pmc then use something else to test. Pmc is awful in my experience.

Test gas tube alignment by removing the bolt head from the carrier and drop the carrier into the upper without a charging handle. There should be no binding when the gas key telescopes over the gas tube. If there is that's one of the problems.

If it still don't run with a buffer and spring swap then swap the bcg from a functioning gun. If that dosent work then its likely the gas port size.

What king of fcg is in the gun?

The lower came complete from Engage. So whatever they use. The ammo that was used was some old bulk ammo I had as well as some new xm193 from federal. Thanks for the help.

-Z

 

[Diesel Kinevel]

I see that you are in Frederick. If you need it, I have a Colt buffer and spring that you can borrow.

Thank you for the offer, I will let you know. Working mids all weekend so i won't get to shoot it until next week sometime.

-Z

 

[CATMdude]

No problem. Stay safe.