AR still won't work

[Sammael94]

Hey all, my AR is still not working. Today I went to my LGS and found they were having a going out of business sale, decided to get the above pictured fore end cap just on the off chance that my gas block was misaligned with the gas port in the barrel and that's why my gun wasn't getting enough gas to operate the action.

Turns out that wasn't the issue (as I'm sure you guessed), but it did bring to light a potential issue with the block its self bleeding gasses completely out of the firearm. The pictured above were taken after firing 9 rounds of IMI surplus ammo during the course of testing my admittedly far-fetched solution to my problem. As you can see, the cap is covered in carbon, and so was the barrel under the gas block when i disassembled this evening. Is all the gas leaking out of my gas block? Is that what's causing my cycling problems? Is my solution to simply get a higher quality gas block? Any input is appreciated. I'm tired of my super cool home built AR not working.

Thanks in advance for your time and help.

 

[LoonWulf]

Have u checked fore and aft alignment as well as side to side alignment? One of my gas blocks sits off the shoulder a bit to align properly.

Also i guess i missed your previous thread but can you describe the problem again?

 

[Sammael94]

Sure, it's been a while since I've posted about this or worked on it (not enough time, limited financial resources, and, honestly, waning interest), so I'm not surprised you don't know what's going on. I should have thought ahead and just described it in the original post, but it kind of sucks doing this on a phone and I just wanted to be done.

Somewhat long-winded excuses out of the way, my problem is that I'm not getting anywhere near enough gas back into the action of my AR to run the action. After each shot, the bolt carrier comes back not even enough to fully cam the bolt out of battery. In my thread before people were suggesting drilling out the gas port to increase gas to the action (which turned out to be a bad idea to try myself with a QPQ barrel and only a woodworking drill press), but I'm not sure that's where the problem is.

And to answer your first question, that's what I got the handguard cap for, to try a different alignment. It actually made the problem worse. I don't know what to do, I could have a gunsmith to drill out my barrel, or I could get a new gas block or a new barrel, but I just don't have the money to keep trying things that may not work.

 

[badkarmamib]

Sounds like either your gas tube is plugged, or, more likely, your gas block port is not mating either with the port in the gas tube or the barrel. Three holes leaves a lot for tolerance stacking...

 

[FL-NC]

You need a better gas block. The "clam shell" ones that have 2 or 3 allen bolts that clamp on from the side are the most reliable in my experience.

 

[tarosean]

and so was the barrel under the gas block when i disassembled this evening.

Sounds like a gas block fitment issue. Do you have a caliper to measure your barrel to ensure one or both are not out of tolerance?

(which turned out to be a bad idea to try myself with a QPQ barrel and only a woodworking drill press), but I'm not sure that's where the problem is.

Did you end up actually drilling it out?

 

[hdwhit]

Sammael94 wrote:
In my thread before people were suggesting drilling out the gas port to increase gas to the action (which turned out to be a bad idea to try myself with a QPQ barrel and only a woodworking drill press), but I'm not sure that's where the problem is.

Since you said this was a home-built gun, please explain in detail:

• What components were used,
  
• Whether the gun ever worked properly (and then stopped working) or simply never worked from the start
• What actions you have taken to try and solve the problem and what happened with each action.

While my first inclination is to say that the problem is that gas is not getting tapped from the barrel and properly fed back to the bold carrier, I don't want to overlook other potential problems (like the piston rings on the back of the bolt are damaged or missing or that gas key is loose).

 

[ClickClickD'oh]

Time for the canned air test.

Step 1: Take your upper off the lower and take the carrier assembly out of the.
Step 2: Duct tape the heck out of your. There are other ways to seal off the muzzle, but you don't want anything that can get stuck in there and everyone has duct tape.
Step 3: Use a standard can of canned air, such as used to clean electronics, and shoot in into the chamber and down the barrel. If you aren't shooting air right back out the gas tube, you have a blockage or alignment issue that needs correcting.

 

[briansmithwins]

You can leak enough gas to make an AR stop working, but you'd need an awful to of it.

They all leak some gas at the gas block when new, the gaps mostly carbon up with use and the leaks taper off.

I agree about making sure you have the gas block alined with the gas port in the barrel, and make sure the gas tube and gas carrier key are also unobstructed. Pics of the relevant parts would be helpful too.

BSW

 

[MistWolf]

Either the gas port is too small, the gas block is leaking, the gas port in the barrel isn't aligned with the port in the gas block, the gas key is loose or the gas rings are missing or damaged.

Let's start with the easy stuff first-
- Use an Allen key to tighten the gas key screws. If there isn't much carbon built up between the carrier & key, this should work.
- Inspect the gas rings. Remove the bolt from the carrier and see if the rings are damaged. There should be three rings, or one continuous ring with three wraps. Don't worry about staggering ring gaps. Ring gap alignment makes no difference. After reinstalling the bolt in the carrier, extend the bolt. With the bolt extended, hold the carrier so the bolt points up. The bolt should not slide back down into the carrier under it's own weight. If it does, the rings are worn and need to be replaced.
- Remove the gas block. On the bottom of the gas block are two set screws. Completely remove the rear set screw and look through the hole. You should see the gas port of the gas block and it should be in line with the set screw hole. Slide the gas block back upside down on the barrel. You should see the gas port of the barrel through the set screw hole and the gas port should be centered. If not, the gas port of the block and the barrel are not lining up, causing partial blockage. I had a barrel with a mis-located gas port and had to grind a little off the back of the gas block to get the ports to line up.
- Inspect the gas tube for blockage. Blow air through it. Don't go poking anything into the gas tube you don't want taking up permanent residence in there, especially cotton swabs or wooden sticks

 

[Sammael94]

I took my bolt carrier apart and cleaned everything, and took pictures of the bolt and gas key. I tried that trick for aligning my gas block and I'll see if that makes any difference.

I don't remember the brands for any of the relevant parts other than that the BCG came from Palmetto State. The barrel, gas block, and gas tube all came from Midway USA and were the cheapest options they had.

It may also be relevant that I'm using a 10.5 inch barrel in a pistol. I posted in rifles because I figured as an AR it's more relevant to this forum even though legally speaking it's a pistol. Anyway, I'm attaching pictures of the bolt and the gas key in case they're helpful.

Thank you all for your help. I really appreciate it.

 

[MistWolf]

How did the gas port of the barrel line up with the set screw hole?

 

[wally]

In my thread before people were suggesting drilling out the gas port to increase gas to the action (which turned out to be a bad idea to try myself with a QPQ barrel and only a woodworking drill press),

I believe I was one of them in your other thread, but I suggested doing it " by hand" using a pin vice to hold the drill and working up starting with the highest number drill (smallest diameter) that doesn't fit freely in the port. I agree its a last resort, but I've had to do it on several "non-standard" builds where the factory port was just about 20% too small in area -- which is not a major change in diameter.

It may also be relevant that I'm using a 10.5 inch barrel in a pistol.

Could be. Is the gas tube "pistol" (~5") or carbine (~7") length? It may sound dumb, but if your 10.5" barrel is drilled for a "carbine" gas tube and you used a "pistol" length tube the tail won't protrude enough to enter the gas key. Unless your bolt photo was taken when new or you cleaned the snot out of it before taking the photo, it looks awfully pristine around the gas rings -- certainly an indication of not much gas flowing through it. Make sure the carrier key is not plugged up!

 

[carbine85]

Does the AR eject and FTF?
Does the AR eject, FTF and not cycle the hammer back?
Check the Gas Key and make sure it's torqued properly. A loose key is a gas leak
A loose receiver extension (buffer tube) can cause a short stroke. The carrier can't travel properly
What size are the ports in the barrel and gas block. I've never seen a defective gas block.
Is the gas tube long enough to reach the gas key?
Does the action manually cycle easily? Check it with a mag installed and dummy rounds.
Have you tried different ammo?

 

[RussellC]

Had the same problem with a 300 BO ar15. If I blew on the gas tube with the valve shut, (adjustable) gas block, I could see vapor of my breath forming where the tube went into the block. I didnt think it was enough to make a difference, but a new block cured the problem.

That said, mine just wouldnt lock back.

Russellc

 

[Sammael94]

I checked the gas key and it's not plugged, neither is the gas tube. I have carbine length tube installed and it mates with the gas key just the same as does the tube in my father's DPMS that has a carbine length gas tube. I haven't tried other ammo, but the same stuff runs flawlessly in my dad's AR. Everything I've checked is tight. I've not put more than 20 rounds through the gun and it's been cleaned a few times, although the bolt wasn't deep cleaned until today.

 

[pert near]

I've never had this problem nor have I tried this fix, but just for what it's worth.
Some say a sloppy gas system fix is to use Permatex gasket sealer when fitting the tube to gas block & when fitting the block to the barrel. I would do this sparingly being careful not to get any in the port. May be worth a try.

 

[wally]

I've never had this problem nor have I tried this fix, but just for what it's worth.
Some say a sloppy gas system fix is to use Permatex gasket sealer when fitting the tube to gas block & when fitting the block to the barrel. I would do this sparingly being careful not to get any in the port. May be worth a try.

Who are some who say?
IMHO that is a really bad idea. The gas block to barrel is in no way a "gasket" type of seal. It relies on precise metal to metal contact and there are several places where tolerance "stack-up" among the parts can cause issues. As Briansmithwins said above, they all will leak a little at least when new. But if its leaking enough to not function, either something is not fitting together right, something is plugging up the gas system (block, tube, or gas key), or the barrel maker screwed the pooch and made the port too small for the barrel length, caliber, and port location (there are some options within a given barrel length for the port location which influences the required diameter of the port).

 

[briansmithwins]

It may also be relevant that I'm using a 10.5 inch barrel in a pistol.

And we have a winner!

That is a problematic build to get to work reliably when not assembled from parts from the clearance bin. I wish you good luck sir.

BSW

 

[pert near]

...Who are some who say?

This advice comes from the owner/gunsmith of AR Performance when building new uppers or diagnosing problem gas systems . Permatex seems like a simple low cost option to test.

Just IMHO...

 

[LoonWulf]

This advice comes from the owner/gunsmith of AR Performance when building new uppers or diagnosing problem gas systems . Permatex seems like a simple low cost option to test.

Just IMHO...

I smear red loctite on the barrel and inside of the block, install, torque then blow air thru to clear the port. I haven't had an issue and no leaks.

 

[Zerodefect]

Looks too loose to me.

I put the block on upside-down. The gas port should be centered in the set screw hole. Not any gap distance between the block and any step on the barrel near the block. Mark the barrel around the gas block. Spin the gas block 180 degrees. Makes sure it's still in the right place. Make sure the dimple is centered.

I prefer the BCM low pro gas blocks.

I have a spare gas block that I drilled all the way through the gas port. I use it as a jig. I put it on, center the hole over the gas port. Tighten the front set screw. Check alignment, Then I drill the rear dimple and put the setscrew in.

 

[Walkalong]

It may also be relevant that I'm using a 10.5 inch barrel in a pistol.

Yes, quite relevant.

 

[MistWolf]

If the gas block ID and the barrel OD are in tolerance, there is no "tolerance stacking". If the gas block fit is too loose, one or the other, or both, are out of tolerance

 

[carbine85]

You still have to check port sizes.