AR15 Cycling Issue

[Csafisher]

Ok help a dummy out….

Putting together a new upper build, took it out for the first time today and it won’t pick up the next round or lock back.

It’s a 11.5” Craddock carbine plus 1 gas system. Superlative arms adj gas block with set screws. Superlative arms bolt carrier and JP bolt. Gas port appears to be around .080” +/- just eyeballing with calipers. Don’t have gauge pins….I triple checked to make sure it was in the all open position. Still building out the lower but put it on an existing lower with a Geissele super 42 carbine spring and H2 buffer. Carbine tube.

I thought it was gas block misalignment but it appears to be fine. I noticed some carbon on the gas tube right at the block. Not sure if that normal. Now wondering if it’s something with the buffer system???

Any ideas? I do have another lower with a geissele spring and h1 buffer to try. As well as another BCG. The one strange pic is the gas block looking into the adjustment area. Couldn’t get it clear. I also put some fishing line down the tube. Didn’t feel any obstructions.

 

[TonyTheTiger]

First guess before seeing your pics was gas port alignment, but that looks good.
Next guess is your JP bolt has the garbage one piece gas ring.

After that if the bolt/carrier/key/gas block are all sealed well enough without some serious leakage I would say it's just undergassed and you need more port diameter.

If it won't run with a standard spring and buffer setup, and you get it to run with a slightly lighter buffer, guess what, it's still gonna be borderline and you'll run into problems eventually if you don't sort the root cause.

 

[Csafisher]

I guess it could actually be over gassed? I didn’t try any other settings but I’ve read that the bolt could just be out running the magazine…. Not sure if that’s true.

 

[Csafisher]

Pics. Ejection was about 4 o clock

 

[oldrifleman]

I guess it actually be over gassed? I didn’t try any other settings but I’ve read that the bolt could just be out running the magazine…. Not sure if that’s true.

Yeah that could be and would be the obvious first thing to check ( and easiest to check). Second is using a verified good magazine.

 

[TonyTheTiger]

I guess it could actually be over gassed? I didn’t try any other settings but I’ve read that the bolt could just be out running the magazine…. Not sure if that’s true.

Could be, some overgassed symptoms can be surprisingly similar to undergassed. I don't put a ton of importance in ejection angle but this is one place that it might help point you in the right direction.
Overgassed rifles also feel like straight up clown shit when they cycle too, so its usually pretty obvious if a gun is so overgassed it won't snag the next round.

Edit: as said above, trying a few magazines is an important and free diagnostic step.

2nd edit: bolt pic definitely looks like a 1 piece. Maybe not THE problem, but a huge problem nevertheless that needs fixing before any other diagnosis is worth doing.

 

[Csafisher]

Could be, some overgassed symptoms can be surprisingly similar to undergassed. I don't put a ton of importance in ejection angle but this is one place that it might help point you in the right direction.
Overgassed rifles also feel like straight up clown shit when they cycle too, so its usually pretty obvious if a gun is so overgassed it won't snag the next round.

Edit: as said above, trying a few magazines is an important and free diagnostic step.

2nd edit: bolt pic definitely looks like a 1 piece. Maybe not THE problem, but a huge problem nevertheless that needs fixing before any other diagnosis is worth doing.

What’s the issue with the JP 1 piece rings?

 

[TonyTheTiger]

They don't work at all and have caused short stroking in every rifle I've tried them in, every time.
Thought I was doing something wrong, consulted with a bunch of my shooting peeps and some JP team shooters (my match shooting stomping grounds extend into MN, JP fanboi territory..) and it turns out they all threw theirs away too.

 

[TheJammar]

Set up a phone and film the bolt in slow motion. See if it’s clearing the mag and where the issue is. Will give good info on gas as well.

 

[bfoosh006]

At the range...

Load one single round into a magazine... insert mag, drop bolt , fire, and see if the bolt catch functions properly. Inspect and let us know the result.

And what specific ammo ( brand , weight , etc ) are you using ?

I would follow SA's adjustment instructions to a "T" as well. ( reread them to make sure )
https://suparms.com/assets/images/Content Images/SA-DIGasBlock-Intructions-090125.pdf

 

[Csafisher]

At the range...

Load one single round into a magazine... insert mag, drop bolt , fire, and see if the bolt catch functions properly. Inspect and let us know the result.

And what specific ammo ( brand , weight , etc ) are you using ?

I would follow SA's adjustment instructions to a "T" as well. ( reread them to make sure )
https://suparms.com/assets/images/Content Images/SA-DIGasBlock-Intructions-090125.pdf

I did and it didn’t lock back. Which makes me think it’s not over gassed but idk.

It was monarch brass 62gr 223 and hornady black. I think 62gr

 

[oldrifleman]

Swap the bolt, I have not had an issue with the JP bolts, but it it is an easy check. Turn the gas block adjustment screw and de if ANY thing changes.
Edit: swap to a fixed gas block and try it. That will tell you if the SA block is working.

 

[B y r o n]

"Note: The 11.5” version uses Craddock Precision’s custom-length gas system called CPO and ships with the custom-length gas tube included. CPO was designed by Craddock Precision to run both suppressed or unsuppressed with a fixed gas block, carbine buffer, and carbine spring. When paired with a “K-can” style suppressor it yields roughly a 16” OAL. Check out the articles on our Knowledge Base discussing our LE-DMR concept which predicated the 11.5” barrel we offer today: [002] The LE-DMR Concept and [014] The LE-DMR Concept pt 2"

As stated, "fixed gas block, carbine buffer, and carbine spring" so your lower doesn't match these components and probably the source of your problem.

 

[JR1200W3]

Do you have a suppressor? Put a high back pressure suppressor on it just as a quick easy test to see if it locks back on an empty mag.

 

[WeR0206]

Ok help a dummy out….

Putting together a new upper build, took it out for the first time today and it won’t pick up the next round or lock back.

It’s a 11.5” Craddock carbine plus 1 gas system. Superlative arms adj gas block with set screws. Superlative arms bolt carrier and JP bolt. Gas port appears to be around .080” +/- just eyeballing with calipers. Don’t have gauge pins….I triple checked to make sure it was in the all open position. Still building out the lower but put it on an existing lower with a Geissele super 42 carbine spring and H2 buffer. Carbine tube.

I thought it was gas block misalignment but it appears to be fine. I noticed some carbon on the gas tube right at the block. Not sure if that normal. Now wondering if it’s something with the buffer system???

Any ideas? I do have another lower with a geissele spring and h1 buffer to try. As well as another BCG. The one strange pic is the gas block looking into the adjustment area. Couldn’t get it clear. I also put some fishing line down the tube. Didn’t feel any obstructions.

Some good suggestions in the thread. In summary I would try swapping to an entirely different BCG (if you don't have a spare make sure your gas key screws aren't loose on the carrier and you have fresh 3 piece gas rings on the bolt) and as others have said a different mag that you know works well (doesn't have "slow" springs/follower etc). Try all of this with a standard strength carbine length spring with standard carbine 3oz buffer. The super42 spring acts almost like an enhanced power spring (similar to sprinco blue) and the H2 buffer might be too much reciprocating mass for your gas port to overcome if it's right on the edge.

Re: ammo if your barrel is 556 or 223 Wylde I would try some 5.56 ammo since it's a little higher pressure unless you want the gun tuned to run on anything (not sure what ammo you usually like to run).

If you're still getting short stroking after all of the above I would look into other areas but start with the above b/c they are cheap/free to troubleshoot besides the ammo.