AR 308 cycling issue

[outdare]

I have a PTAC AR 308 that I have built. It has a 18" cmmg barrel, slash heavy buffer, syrac adjustable gas block, ASR muzzle break and a PSA 308 bcg.

The main problem is the bolt gets stuck closed. I was able to muscle it open after some fidgeting. I have the adj. gas block open and the bcg would still hang closed. I was running the bcg wet for break in. I pushed through this and the bcg started to free up. Eventually the bolt would fte with the empty case in the receiver. I would have to hand cycle the charging handle to chamber the next round till I put the specwar on. With the silencer on it would cycle no issues.

So my first question is the heavy buffer too much with the adjustable gas block?

I had a gun smith verify the head clearance. The gun will hand cycle without any issues cold. Will the barrel and bcg lap each other till it fits correctly?
Should I try to polish the bolt where it mates with the barrel?

Thanks

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[Ole Cowboy]

If its cycling OK with the silencer on nut is slamming the door hard without, then it sounds like an overpressure issue at first blush, can you dial it back?

What length is the barrel and are you using the correct length of gas system for that length of bbl?

Your pics tell the story, especially the one of your brass, the BCG is hitting it HARD, look at the damage its doing.

The heavy buffer may not be reacting fast enough. No based upon your pics it will not lap in.

I don't think the problem has its origin in anything but overpressure. Polishing it out would only be a band-aid solution.

 

[outdare]

The barrel is a 18" cmmg rifle length gas. I had a gunsmith look this over when it was painted. The extractor spring has been updated. The bolt was not moving. The first shot it jammed up. I had to work to get the bolt to open again. I can turn the gas off. I just kept opening it as I went to try to get the bolt to cycle. I'm thinking that the bolt I have is not going to work with this barrel. I did start closing the gas off when the can was on.

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[Ole Cowboy]

The barrel is a 18" cmmg rifle length gas. I had a gunsmith look this over when it was painted. The extractor spring has been updated. The bolt was not moving. The first shot it jammed up. I had to work to get the bolt to open again. I can turn the gas off. I just kept opening it as I went to try to get the bolt to cycle. I'm thinking that the bolt I have is not going to work with this barrel. I did start closing the gas off when the can was on.

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You may be correct with that BCG.

Gas, Buffer, BCG:

All of the above, some of the above one of the above.

FWIW I build to OEM spec, then I mod from there. This makes it easy to identify the issue. If it works properly in OEM trim and you add a component and you have issues, then you know where to begin. Since you have added a can and you want performance from both w/wo a can and it appears to function properly with the can then the issue may well be the BCG. Go back to the mfg of your BCG and pose the question to them...

 

[grasshopperglock]

So the smith ran a Go and No-Go gauge through it? Seems from everything you say and the casing getting overly compressed on the rim.

The headspace is tight or the NATO ammo has a too long OAL on the casing shoulder.

 

[outdare]

I ran 3 different types of ammo. Freedom Munitions, Federal, and Fusion all 168gr. All the cases looked the same. PSA is the bolt manufacturer. They said I am SOL. They don't warranty anything but their own barrels. I have a call into CMMG. Waiting for a response. Is there a goto BCG for 308/7.62X51?

 

[Sam7sf]

I ran 3 different types of ammo. Freedom Munitions, Federal, and Fusion all 168gr. All the cases looked the same. PSA is the bolt manufacturer. They said I am SOL. They don't warranty anything but their own barrels. I have a call into CMMG. Waiting for a response. Is there a goto BCG for 308/7.62X51?

Stag. There is better and some may scratch their heads at me suggesting them but I have never gotten anything out of spec from them. And I'm talking a lot of rifles. For the price, buy stag parts and don't look back.

Edit: I also trust anything from bcm.

 

[outdare]

I spoke with PSA again and they are going to exchange the bcg. On another note how far out is a rifle length gas tube suppose to stick out. I can slide the bcg up to a point of resistance. I have included some pictures. Thanks

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[Sam7sf]

. I can slide the bcg up to a point of resistance.

So you're not supposed to get much resistance. If there is a little hiccup is fine but you shouldn't feel like it takes any force from your fingers or hand to slide the key over. Take your upper and stripped carrier, insert the carrier half way in or higher, tilt your upper at whatever you feel is a 45 degree angle. Eye it. Drop the carrier. Let it fall onto the gas tube. If it has an issue, you have sealing issues. Your length that its sticking out looks fine.

 

[grasshopperglock]

Clean off the gas tube nipple. Color the bare areas with a Sharpie marker. Cycle the bolt a few times and see if the wear is even all the way around the nipple. If its not, the gas tube needs to be tweaked until it uniformly enters the bolt key. (The gas tube is centered to the gas key)

As for length, I don't know. I don't think the gas key is shallow enough for an out of spec gas tube to bottom out inside the gas key. Make sure the gas tube is fully seated in the gas block just to make sure.

Edit: wanted to add. If you have to bend the tube to center. Flex the tube by the barrel. See if the flex moves the nipple any discernable amount. If you can get it centered by flexing it. You don't have to take it off and bend it by hand. Reinstall, check alignment, rinse and repeat. Don't stick a screwdriver to try and adjust the tube in the charging handle pathway. Nicks and gouges will mess up the upper receiver. The tube is easy to bend. Use something wood if you go that route. Or something plastic. Flex it gently.

 

[outdare]

How tight of fit is the gas block supposed to have? Here is the result of the rub test. I mark several surfaces to see which would stand out.

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[outdare]

Here is a pic of the bcg. It seems to rubbing by the gas key. At this point I am going to send the bcg back to PSA and see if a new one will fix this issue.

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[Sam7sf]

Send that whole upper back.

 

[Big Green]

In addition to the above, have you tried a lighter buffer? You said it cycles fine with the can but not without? What does it do when you open up the gas block unsuppressed?

I have a PSA 308 that I've only fired a mag out of to ensure it properly functioned. I will say that even charging the weapon empty is a completely different experience than my 556 sized ARs. Mil spec charging handle is nearly worthless, I upgraded to a Raptor LT which helps.

 

[ed308]

Here is a pic of the bcg. It seems to rubbing by the gas key. At this point I am going to send the bcg back to PSA and see if a new one will fix this issue. View attachment 137966 View attachment 137967 Sent from my SM-N920V using Tapatalk

The top of the gas key look like it's dented. It should be perfectly round. Also, the gas tube looks like it's slightly canted to one side (common mistake). But it may the be the angle of the picture. Try working the bolt in and out of position into the barrel extension without a round. Feel how smooth it works. Then try it with the gas key removed from the bolt carrier. If smoother without the gas key installed, you'll know the gas key it getting hung up gas tube.

I don't know how many rounds you've fired in the AR, but it can easily take 100 rounds for everything to seat properly. Looking at the feed ramps, there is a small lip on the barrel extension. You could smooth that lip out with a Dremel tool. Just knock off the lip where the bullet tip can't get hung up on it. Or leave it and the lip will eventually wear down on its own.

Most AR10 are going to be over-gassed and will cause swirl marks like what you see on the photos of your brass. An adjustable gas block will fix that problem. But it looks like yours is wide open. Heavier buffers and springs are really nothing more than a band aide fix. They don't address the problem. Most of my 6.5 CM/.308 ARs only need a little more than one full turn to run smoothy and not tear up the brass. Manufacturers make their ARs over gassed so they run with every ammo brand you feed it. So start with adjustable gas block turn all the way down then open it up till it cycle smoothly for the ammo your shooting.

When you get the upper back, work the charging handle and bolt back and forth 200-300 times. That can really help with break-in instead of using ammo. Run it wet. That always helps but keep it out of the chamber. I would get the AR running smoothly before adding the silencer. That's just adds one more element to deal with.

 

[popper]

Possible the AGB is mounted against the shoulder - it should be ~0.1 off - will make the gas tube possible too long. Loosen it, close bolt and push AGB to where it should be. What causes the case head damage? Ejector or extractor? If you cycles that case several times and the ejector did it, it's hanging somehow.
Both my LR308 bolts close with a gentle press of the thumb on the BCG add a case it's not too much harder but the ejector spring is strong. BCG will get worn on the side of the bolt pin, corners of the sliding parts of the carrier. Watch for excessive grooving of the bolt pin where it goes into the carrier.

 

[outdare]

So I bought the bcg in 2015 It is a multi year build. Kinda like Johnny Cash's Cadillac song. I did some research and I found examples of the extractor spring being to strong. This will cause the case damage seen in the picture.

To answer some of the questions. I have tried adjusting the gas block from full close to completely open. I have 120 rounds through this gun mixed commercial ammo. I may try to do the extractor spring fix and see if that works before I send the bcg back to PSA.

Lastly I did dry cycle the rifle several hundred times before my first range trip.


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[ed308]

I doubt it's the spring. Looking at your ejector, it's flat. Chamfering or removing the sharp edges on the ejector will help. But those marks are common on .308, 6.8, 6.5 Grendel and other high powered rounds that are over gassed. Your adjustable gas block should be open just enough to run smoothly.

Here's good article on chamfering the ejector:

http://bulletin.accurateshooter.com...-improved-reliability-with-larger-cartridges/

 

[popper]

Extractor pulls the case out and can bend/rip the rim. Ejector tossed the case out strong spring will dent the case head. Your can increases pressure. Extractor marks usually aren't that big, but if it is not moving correctly it will (should) roll over the rim. Looks more like ejector swipe to me. The round pin has to move back and allow the bolt to rotate to close (or open). It will hold the case head off the bolt face a few thous. but if head space isn't correct, it can jam the case against the shoulder. When fired, bolt tries to open (rotate) but the pin holds case head and tried to prevent rotating. Actually tries to rotate the case in the chamber. It also forces the back of the bolt lugs against the extension lugs so a LOT of force is needed to open the bolt. Called ejector swipe, see it on a lot of picked up 223 brass. My SWAG, H.S. is NOT right.

 

[outdare]

I removed the bcg today and checked the ejector. I could not get the ejector to move. It would not depress etc. That explains the marks on the brass.
I packaged up the bcg and sent it back to PSA. We'll see if this fixes my issue.

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