AR10 (.308) Home Build Problem Child - Won’t Cycle

[jab00]

I need some help/input trying to solve the latest problem with my AR10 home build.

Problem Description:

The rifle will not chamber a second round or lock-back on a empty mag, even with the gas block wide open.

Possible related problem: I noticed with the KAK buffer spring that there was seemingly more resistance than expected when I pulled the charging handle back and it was very difficult to release the bolt. This issue seemed to improve slightly after I change to the Orange spring with two coils removed but it still seems stiffer than any other gun that I’ve got

Things That I’ve Checked and Solutions That I’ve tried:

• Checked that gas block is aligned and tightened down properly
• Checked gas rings in the bolt to make sure that they’re staggered
• Buffer System Config #1: KAK heavy (blue) buffer with KAK 308 carbine buffer spring
• Buffer System Config #2: DPMS 3.8 oz buffer with Springco Orange spring with two coils cut
• 147 grain and 168 grain ammo with both spring combos

Parts List:

• Aero Precision Upper
• Aero Precision BCG
• Aero Precision 16” mid-length gas barrel
• Superlative Arms bleed off gas block
• Aero Precision mid-length gas tube

Questions:

• Should I keep cutting coils on the spring until it cycles?

 

[Spblademaker]

16 clicks out on superlative is wide open.
Gas block shimmed at .025-.030

 

[jab00]

16 clicks out on superlative is wide open.
Gas block shimmed at .025-.030

I did four full rotations from fully closed. I guess I’ll close it up again and count 16 clicks and take trip to Home Depot for some feeler gauges

 

[DRAM40A1]

Yes, check that you are actually fully open. 4.5 turns out from fully closed. Also from what I read, the orange spring is for severely overgassed rifle. Use the red spring. In fact, the best thing is to run an extended length receiver extension, 3/4 longer than carbine, with an H3 buffer and either red spring or an Armalite AR10 spring.

 

[Spblademaker]

Thanks Dram. Just found my install card. 18 clicks, not 16 like I stated.

 

[jab00]

Yes, check that you are actually fully open. 4.5 turns out from fully closed. Also from what I read, the orange spring is for severely overgassed rifle. Use the red spring. In fact, the best thing is to run an extended length receiver extension, 3/4 longer than carbine, with an H3 buffer and either red spring or an Armalite AR10 spring.

So, right now I’ve got a Daniel Defense 6 position carbine buffer tube on the gun. Should I try swapping out the Orange spring for an Armslite spring and try that out with the 3.8 oz buffer and see what happens before I swap buffer tubes?

 

[DRAM40A1]

You want the extended length tube with a 5.4 ounce H3 buffer. Armalite sells a kit with the tube, buffer, spring for $55. I think it will cure your issues.

 

[DRAM40A1]

I don’t know how to share a link from my phone but this is a deal. $55
Both KAC and LMT use the extended length tube and standard carbine length buffers. BTW, I have a BA 16” mid gas barrel and it runs great with this combo. Edit to add I’m using a standard gas block.

 

[jab00]

I don’t know how to share a link from my phone but this is a deal. $55
Both KAC and LMT use the extended length tube and standard carbine length buffers. BTW, I have a BA 16” mid gas barrel and it runs great with this combo.

Great - thanks! I'll jump onto Armalite's website and take a look at the kit.

 

[DRAM40A1]

I bought another recently and had to call them because of an issue with ordering from the link. They may have fixed it by now but fair warning, it goes out of stock often.

 

[mewillis]

I just did the carbine conversion on my SASS, if you want your stock to fully close you will need buffer tube 10207027 which
is a 7 position tube. the kit has the 6 position and won't fully close. just a heads up..........

 

[MolassesTreeJ]

Are you certain the parts stackup is correct? Such as, if you are using the m4 'carbine' receiver extension, you need need the proper dpms ar308 carbine buffer.

However, using the a5 length receiver extension will allow using the ar15 h3 carbine buffer.

Make sure nothing is binding or impacting.

Use a5 buffer tube, h3 buffer and the superior shooting system ar10 flatwire recoil spring. Or the proper rifle length setup..

Next, make sure the gas tube is not shrouded inside the gasblock. Sometimes the mass machined parts are off. I had a gas tube that when pinned in the block, was 50% obscured/shrouded. The hole in gastube was poorly cut. So, I used a drillbit that matched the gasblock port size to 'ream' the gastube. A few wraps of 3m electrical tape on sides of drillbit to prevent chewing up the gasblock, a little pressure. Excellent.

Also, are you bumping the shoulder back enough to properly chamber those reloads?

There is a number of problems it could be.

Tell us what is happening when it 'fails to chamber'? If it does not lock back, it sounds undergassed. No spring should be strong enough to prevent full gas on a mid length system from locking back unless there is a mechanical fault.

Are you having pinched brass?

What direction does the brass throw? How far?

 

[jab00]

Are you certain the parts stackup is correct? Such as, if you are using the m4 'carbine' receiver extension, you need need the proper dpms ar308 carbine buffer.

However, using the a5 length receiver extension will allow using the ar15 h3 carbine buffer.

Make sure nothing is binding or impacting.

Use a5 buffer tube, h3 buffer and the superior shooting system ar10 flatwire recoil spring. Or the proper rifle length setup..

Next, make sure the gas tube is not shrouded inside the gasblock. Sometimes the mass machined parts are off. I had a gas tube that when pinned in the block, was 50% obscured/shrouded. The hole in gastube was poorly cut. So, I used a drillbit that matched the gasblock port size to 'ream' the gastube. A few wraps of 3m electrical tape on sides of drillbit to prevent chewing up the gasblock, a little pressure. Excellent.

Also, are you bumping the shoulder back enough to properly chamber those reloads?

There is a number of problems it could be.

Tell us what is happening when it 'fails to chamber'? If it does not lock back, it sounds undergassed. No spring should be strong enough to prevent full gas on a mid length system from locking back unless there is a mechanical fault.

Are you having pinched brass?

What direction does the brass throw? How far?

Right now, the BCG isn’t moving rearward at all when a round is fired (it’s acting like a straight pull where I have to pull the CH to chamber the next round). I had someone watch the ejection port while I pull the trigger and they said that the BCG isn’t moving at all when the round goes off.

Nothing seems to be binding when I pull the CH back manually. The only thing that I’ve observed is that the Bolt Release is exceptionally tight with both springs (the KAK and the trimmed Orange)

I can’t say anything about the ejection pattern yet since I’ve yet to get the system to cycle at all (this is leading me to believe the root cause has to be something in the gas system since, as you mentioned, nothing should prevent “full gas” from cycling the s ruin)

I’ll take some pics of everything and post them so that everyone can see what I’m dealing with)

 

[jab00]

I just did the carbine conversion on my SASS, if you want your stock to fully close you will need buffer tube 10207027 which
is a 7 position tube. the kit has the 6 position and won't fully close. just a heads up..........

Luckily, the state of New Jersey has resolved all collapsible stock issues by banning them on semiautos

 

[padom]

Right now, the BCG isn’t moving rearward at all when a round is fired (it’s acting like a straight pull where I have to pull the CH to chamber the next round). I had someone watch the ejection port while I pull the trigger and they said that the BCG isn’t moving at all when the round goes off.

Nothing seems to be binding when I pull the CH back manually. The only thing that I’ve observed is that the Bolt Release is exceptionally tight with both springs (the KAK and the trimmed Orange)

I can’t say anything about the ejection pattern yet since I’ve yet to get the system to cycle at all (this is leading me to believe the root cause has to be something in the gas system since, as you mentioned, nothing should prevent “full gas” from cycling the s ruin)

I’ll take some pics of everything and post them so that everyone can see what I’m dealing with)

If your bcg isnt moving backward at all when you fire a round it's not a buffer issue. You have a gas issue. Bad gas block, gas port hole properly aligned with hole in block. Not just side to side, but front to back as well. When you remove the block, what do you see around the gas port burn wise? Bad gas tube... proper gas tube...

 

[jab00]

If your bcg isnt moving backward at all when you fire a round it's not a buffer issue. You have a gas issue. Bad gas block, gas port hole properly aligned with hole in block. Not just side to side, but front to back as well. When you remove the block, what do you see around the gas port burn wise? Bad gas tube... proper gas tube...

I just pulled the block off of the port and there was some “burn” around the port. I just used some feeler gauges and retightened the block .027” from the shoulder and checked to make sure that it’s lined up with the port.

One thing I did notice is that it looks like I made have had the block a little too far out based on that line that I circled in red (previous block position)

The gas tube inside the upper looks unremarkable. The gas key slides in freely and the opening looks clean

 

[hlee]

In addition to the line on the barrel, it appears that there is an impression of a small circle in front (to the left in the picture) of the gas port on the barrel. If that is not my eyes deceiving me, it looks like you had the gas port completely occluded by the gas block.

 

[2ndamendfan]

In addition to the line on the barrel, it appears that there is an impression of a small circle in front (to the left in the picture) of the gas port on the barrel. If that is not my eyes deceiving me, it looks like you had the gas port completely occluded by the gas block.

Yep, I see it also.

 

[DRAM40A1]

That’s what I’m seeing as well.

 

[SupressYourself]

Also make sure your gas tube is not installed in the block upside down. My brother did that once.

To check gas flow, you can plug the chamber with something and blow air (with a compressor) down the bore from the muzzle end. If air doesn't come out the tube on the chamber end, something is out of alignment.

 

[MolassesTreeJ]

I have found some gasblocks and barrel dimples.. do not line up properly..

I normally measure the edge of gasblock to port. Then, use a sharpie or white grease pen to mark 'guide lines' on the barrel. So I get the gasport lined up with the gasblock. I mark centerline of the barrel gasport on barrel shoulder. Then, slide the block where it needs to be in relation. Generally the gasblock is a 0.125" hole which compensates for the ~.030" of handguard shim not in place. This oversize also helps with being slightly clocked. So, minor offset of gasblock also usually has very few issues..

One time I had a barrel with the dimple drilled at 0430oclock, not six. It had a similar issue like you are showing.

Hope this helps.

 

[padom]

I see a gas block hole not centered over the gas port. You appear to be blocking it as others have said

 

[2aBaC̶a̶]

There's probably a carbon spot on the inside of your gas block where the barrel port was.

1. Verify tube hole lines up with gas block hole. If you can't get a visual through a screw hole, you can blow air through it and should feel no resistance, same as the tube off.
2. Verify gas block hole lines up with barell hole. Using some calipers measure the hole from shoulder of the barrel and compare it to the hole from the end of the gas block that touches the shoulder. That will give you the amount needed to shim.

 

[jab00]

Thanks for the observations above, I believe that you guys are narrowing in on my issue. I really appreciate it!

Does anyone happen to have a Superlative gas block laying around that they could measure the edge of the gasblock to the center of the port for me? I hate to ask for someone to do this but, among the other many "benefits" of living in New Jersey, they require that all muzzle devices be permanently attached so I can't get to the underside of my block any more?

I found a schematic of the block on the Superlative Arms website but it doesn't indicate where the port is (just the outside dimensions)

 

[padom]

Thanks for the observations above, I believe that you guys are narrowing in on my issue. I really appreciate it!

Does anyone happen to have a Superlative gas block laying around that they could measure the edge of the gasblock to the center of the port for me? I hate to ask for someone to do this but, among the other many "benefits" of living in New Jersey, they require that all muzzle devices be permanently attached so I can't get to the underside of my block any more?

I found a schematic of the block on the Superlative Arms website but it doesn't indicate where the port is (just the outside dimensions)

Which block do you have? .936?

 

[srt-4_uk]

Plug chamber
Put air down muzzle
Move gas block around until it air flows most freely
Secure it

 

[jab00]

Which block do you have? .936?

.750

 

[DRAM40A1]

My .750 SA is very near .260 to the center. If you secure it .025 forward of the shoulder, it will line up.

 

[DRAM40A1]

Also your rear screw of the block is in line with the gas port. Just an FYI.

 

[jab00]

My .750 SA is very near .260 to the center. If you secure it .025 forward of the shoulder, it will line up.

Thanks. I just pulled out my feeler gauges and secured it at .025 and checked to make sure that the adjustment screw is centered on the line that I drew from the center of the gas port on the barrel. I’ll take the gun to the range next weekend and post an update

ETA: Another lesson for myself about the importance of reading directions from time to time.. If I had just flipped over the piece of cardboard that was in the package with the gas block, I would have seen the explicit instructions to use the feeler gauges to space the block .025" from the shoulder

 

[2aBaC̶a̶]

I use a little 1/4" rubber hose attached to the gas tube inside the upper to blow air through (using my mouth). I also use a little lock tight around the hole to seal it up.

Good luck.

 

[jab00]

Problem solved, thanks guys!

I took the rifle back to the range this morning and it’s cycling just fine after moving the gas block.

Thanks again!