AR new barrel cycling issues

[Shoebox]

Hello all, I've been reading here for a while, but this is my first post. I've read several other threads with similar issues, but every situation is different, so I figured I'd ask about my own situation.

Currently equipped:
PSA upper and lower receivers
BA 18" Stainless .223 Wylde rifle-length barrel
Toolcraft nickel-boron BCG
Aero Precision stainless rifle-length gas tube
No name basic .750 gas block
Tubb flat buffer spring with 2-3 coils removed
Odin adjustable buffer, currently about 2 oz
Rise RA-140 trigger
Strike ambi mag release

I have what started out as a basic PSA 16" carbine-length 5.56/.223 AR. First upgrade after about a year was a Rise RA-140SST drop in trigger. I was never happy with the accuracy of the barrel, so I was leaning toward a Faxon or BA 20" rifle-length .223 Wylde. JoeBob's had a great deal on an 18" BA rifle-length stainless barrel, so I jumped on that, with a Kaw Valley gas block and JoeBob's stainless gas tube. I dimpled the barrel for the gas block using a Kaw Valley dimpling jig. Also swapped to a Toolcraft nickel-boron BCG at the same time.

First time firing it, regardless of ammo type, it was short stroking and not locking back on an empty mag. Gas was blowing out everywhere around the gas block. I contacted Kaw Valley, and they sent out a replacement gas block. This one seemed to seal properly, and factory Norma 55gr .223, Winchester 55gr 5.56, and Winchester 62gr 5.56 all cycled properly and would lock back empty, as would a CFE223 55gr FMJ @ 26.3gr load. However, 55gr FMJ over 22.4 H335 and 24.0 AR Comp that ran reliably with the original 16" barrel would not lock back, and the AR comp was hit or miss whether it would cycle a subsequent round reliably.

I swapped out the buffer spring and buffer for a Tubb flat spring and Odin adjustable buffer. Tried various weights from 1.5oz to 4.5 oz, with no change. I tried 2 different BCGs, with no change. Tested the BCG with bolt removed to check gas tube fit, no issue. Tested to make sure the gas block was aligned (though the dimpling jig ensured it would be, and removing the block I could see the holes matched up perfectly) by blowing air through with the barrel plugged. Gas key is tight and properly staked. Thoroughly lubed the bcg.

Around this time, I also tried new, hotter H335 loads, from 24.3-25.2gr, with no change to cycling at all.

Called Tubb to see if they have a lighter weight flat spring, and was advised to try cutting off 3 coils. Swapped out to a basic, no-name gas block my buddy sent me to try, with a new Aero Precision gas tube installed. The new gas block actually had a much tighter fit around the barrel journal than the Kaw Valley did, so I was encouraged. Tested these changes today at the range, but no real change.

No real change, although today at the range for some reason the bolt wouldn't reliably lock back on any ammo but the CFE223 reloads, and wouldn't even reliably lock back when I cycled the bolt via the charging handle on an empty mag. I also was able to chrono the ammo I shot today - factory loads were 3000-3100fps, H335 22.3gr was around 2700fps, AR Comp 24.0 gr @ 3000fps, and CFE223 26.3 @ 2800fps.

I am pretty certain there is no real problem with the lower, as I have a PSA 16" 300blk upper that I also shot the same days on it, and it cycled reliably no matter what changes I made to the spring or buffer.

At this point I am at a loss. The only other thing I can think to try is to have the gas port enlarged from the 0.093" it is now to something larger, maybe 0.100"? I will try spinning the bolt in the chamber to ensure it turns freely, but that's about the only thing I've read on other threads that I haven't tried. My LGS and the gunsmith at the range were stumped as well.

Does anyone have any other ideas of anything I'm missing?

 

[KZP]

and wouldn't even reliably lock back when I cycled the bolt via the charging handle on an empty mag

Did you try various brands of magazines? How much contact is your bolt catch making with your BCG?

 

[Shoebox]

Did you try various brands of magazines? How much contact is your bolt catch making with your BCG?

Yes, I tried 6 different Pmags, Amend, and metal magazines.

I need to check that, today was a new issue with the bolt not catching when I manually pulled it back.

 

[Shoebox]

How much contact is your bolt catch making with your BCG?

It's firmly held back. I can't tell as the bcg is traveling back over it, but there isn't really any wear on the catch.

 

[KZP]

How much over travel does the BCG have past the catch? Mine looks to be about 0.25"

 

[FCS]

18” bbl, rifle gas system, 0.093” diameter port, correct?

0.093” diameter port is normal for 20”, rifle gas system.
Probably need 0.098” to run w/o using suppressor, maybe as large as 0.102” but easier to open port so I’d recommend starting at 0.098”.

 

[Evintos]

No real change, although today at the range for some reason the bolt wouldn't reliably lock back on any ammo but the CFE223 reloads, and wouldn't even reliably lock back when I cycled the bolt via the charging handle on an empty mag. I also was able to chrono the ammo I shot today - factory loads were 3000-3100fps, H335 22.3gr was around 2700fps, AR Comp 24.0 gr @ 3000fps, and CFE223 26.3 @ 2800fps.

What direction is your empty brass ejecting? MK12 SPR gas port diameter is at 0.100" to 0.105 however military gas port diameters tend to be over sized to begin with necessitating heavier buffer mass. Even at 0.093" you might still be overgassed from 1.5 to 4.5oz that you've tested (and roughly the 2oz you've settled at currently). You may actually need 5oz or more and the failure with lock back on empty may be a sign of bolt overrun.

Make sure that the bolt catch is able to utilize its full range of motion. Remove the upper, pull on the bolt catch to ensure there's no excessive play/wobble. It should move freely when you use a finger to pivot the bolt catch outwards. If it's binding, it could be a broken bolt catch spring, broken bolt catch detent, broken bolt catch. Inspect the bolt catch lug for damage.

Assuming nothing is wrong with the bolt catch, inspect carrier gas key and lower castle tower for damage or wear. Inspect clearance available at full lock back. Easy test is as @KZP mentioned, look for BCG overtravel past bolt catch lock, some overtravel is a good thing. More difficult but not necessary test - remove the charging handle, leave BCG in, insert empty magazine, with a pen, punch, or finger (be careful with the finger) move the BCG back until it is locked to the wear with empty mag. There should be a gap between the castle tower and the rear of the gas key (side note: the smaller the gap without touching the castle tower at full compression the better). The rear of the gas key should be roughly half way or past midpoint but not touching the castle tower at lock back. Example image below. If the gap is excessive or gas key is less than midpoint, the following could be the issue/s causing incorrect stroke length:
1. Buffer bumper not properly compressing. Incorrect durometer material or bumper too long
2. Incorrect buffer body length
3. Excessive spring length. At full spring compression, compressed coils prevents buffer and BCG from reaching far enough into the receiver extension/buffer tube.
4. Gas key dimensions too long (although not likely because you've tried another BCG).

Some of these can be remedied by backing your receiver extension 1 or more revolutions out assuming it can still retain the buffer detent.

 

[Tiribulus]

Just to throw it out there, I recently bought a BA barrel and the port was undersized. Shoots great once I opened it up a hait, but wouldn't lock back no matter what before I did. A trivial operation. Took a few minutes.

 

[Shoebox]

Just to throw it out there, I recently bought a BA barrel and the port was undersized. Shoots great once I opened it up a hait, but wouldn't lock back no matter what before I did. A trivial operation. Took a few minutes.

I'm thinking that's going to ultimately be the solution. I'll try Evintos' suggestions first. I won't be opening up the port myself though, I'll leave that to a gunsmith, as every time I've ever drilled a hole in metal there's always a jagged edge or burr on the back side and I have no way of cleaning that up.

 

[n0glock]

New quality drill bit, cutting oil, go slow, you already have a pilot hole.

 

[Tiribulus]

New quality drill bit, cutting oil, go slow, you already have a pilot hole.

And put a cleaning rod in the bore to protect against accidental over drilling. Don't want to gouge the rifling on the other side from the port. I used a carbide bit. Make sure it's the right size LOL. I used digital calipers.

 

[Tiribulus]

I'm thinking that's going to ultimately be the solution. I'll try Evintos' suggestions first. I won't be opening up the port myself though, I'll leave that to a gunsmith, as every time I've ever drilled a hole in metal there's always a jagged edge or burr on the back side and I have no way of cleaning that up.

Once I had it done, I used the bit , turning it by hand to clean it up and then ran a bore snake through it a couple times. 100% good to go several hundred rounds later. Shoots great.

I would make it the path of last resort though. If something else fixes it, then that should be the fix imho. Mine was definitely undersized though. .053 from the factory. That's too small for a carbine length 16in. barrel. I opened it up to .065. Could have gone a little more, but that completely fixed the problem.

 

[bfoosh006]

Every thing wet with lube ? The bolt head photo looks a little dry .

 

[Shoebox]

What direction is your empty brass ejecting? MK12 SPR gas port diameter is at 0.100" to 0.105 however military gas port diameters tend to be over sized to begin with necessitating heavier buffer mass. Even at 0.093" you might still be overgassed from 1.5 to 4.5oz that you've tested (and roughly the 2oz you've settled at currently). You may actually need 5oz or more and the failure with lock back on empty may be a sign of bolt overrun.

Thanks for all the ideas!

Hard to tell direction because I'm troubleshooting at an indoor range with stalls. Appears to eject 3-4 o'clock. There is no way it's overgassed, but I bumped the weight of the adjustable buffer up to H3 weight for testing tomorrow at an outdoor range, just to see. I'll be able to tell ejection direction better as well.

Make sure that the bolt catch is able to utilize its full range of motion. Remove the upper, pull on the bolt catch to ensure there's no excessive play/wobble. It should move freely when you use a finger to pivot the bolt catch outwards. If it's binding, it could be a broken bolt catch spring, broken bolt catch detent, broken bolt catch. Inspect the bolt catch lug for damage.

Bolt catch is in good shape, moves freely, no damage.

Assuming nothing is wrong with the bolt catch, inspect carrier gas key and lower castle tower for damage or wear. Inspect clearance available at full lock back. Easy test is as @KZP mentioned, look for BCG overtravel past bolt catch lock, some overtravel is a good thing. More difficult but not necessary test - remove the charging handle, leave BCG in, insert empty magazine, with a pen, punch, or finger (be careful with the finger) move the BCG back until it is locked to the wear with empty mag. There should be a gap between the castle tower and the rear of the gas key (side note: the smaller the gap without touching the castle tower at full compression the better). The rear of the gas key should be roughly half way or past midpoint but not touching the castle tower at lock back. Example image below. If the gap is excessive or gas key is less than midpoint, the following could be the issue/s causing incorrect stroke length:
1. Buffer bumper not properly compressing. Incorrect durometer material or bumper too long
2. Incorrect buffer body length
3. Excessive spring length. At full spring compression, compressed coils prevents buffer and BCG from reaching far enough into the receiver extension/buffer tube.
4. Gas key dimensions too long (although not likely because you've tried another BCG).

Some of these can be remedied by backing your receiver extension 1 or more revolutions out assuming it can still retain the buffer detent.

The bolt is a little over 1/4" from the catch when pulled fully back with the CH. Removed the CH, did your test, its about exactly halfway. I have 2 springs, the milspec PSA carbine spring that came with it and a Tubb flat spring with 2-3 coils cut off. Spring compression is ok. I also have 2 buffers, the milspec carbine PSA buffer and the new adjustable Odin Works buffer. Both are in good condition.

I should reiterate that this lower functions perfectly with an unmodified 16" PSA 300blk upper with pistol-length gas system, regardless of which spring or buffer/weight I use, or which ammo I run through it - factory or reloads, super or sub.

 

[Shoebox]

Every thing wet with lube ? The bolt head photo looks a little dry .

I knew someone would comment on the bcg LOL. The one in the picture is the BCG from my 300blk upper. I had been cleaning both BCGs and the bolt from the .223 upper disappeared somewhere when I wanted to test that and get a pic, so I threw the dry 300blk BCG in there. Yes, they're both properly lubed when shooting.

 

[Shoebox]

To follow up, I have tried all the suggestions in this and mkrem's thread.

The latest attempt was installing a Breek Arms adjustable gas block and stainless rifle length tube. For those keeping score, that's gas block and tube #4. I opened the block completely, and the rifle wouldn't cycle any ammo at all. Basically bolt action. Removed it when I got home, everything was aligned and I could blow freely through the tube and block. So that block is basically useless to me, as even wide open it's too restrictive.

 

[Tiribulus]

Wide open is going to be the same as not having an adjustable gas block.

 

[Tiribulus]

Man. .093 is pretty big. At this point it can't hurt to take it out a little bit it would seem.

 

[Shoebox]

Man. .093 is pretty big. At this point it can't hurt to take it out a little bit it would seem.

It didn't even eject the spent case. I don't think closing it any would help. Worst case, I open the port and it's a little over gassed, I have an adjustable block to tame it a bit.

 

[KZP]

What do the rims of your fired cases look like, are they visibly bent? Wonder if they are getting stuck in the chamber and it's causing your BCG to lose momentum.

 

[Evintos]

Not ejecting a spent case can actually be a sign of overgassing. What happens is, your bolt unlocks and begins it's rearward travel before the brass in the chamber has a chance to contract enough to allow extraction as the pressure in the bore is still too high.

I'm assuming you've tried increasing buffer weight to 5+oz. If you're sure you're not overgassed next step would be at this point since all other attempts have failed will be drilling the gas port. To start off with aim for 0.100" to 0.105"

 

[Tiribulus]

It didn't even eject the spent case. I don't think closing it any would help. Worst case, I open the port and it's a little over gassed, I have an adjustable block to tame it a bit.

Please don't take this the wrong way. We don't know each other at all. Are you absolutely sure you have the right measurement on that port?

I don't know how it could be that big and not even eject the spent case. Even when mine were quite undersized, they both still at least ejected the cases.

 

[Shoebox]

What do the rims of your fired cases look like, are they visibly bent? Wonder if they are getting stuck in the chamber and it's causing your BCG to lose momentum.

Case rims are fine. The only markings on the brass are a scratch neck-to-shoulder from a sharp edge on the star chamber on ejection.

 

[Jsp556]

I have an 18” barrel with the same port size. Mine works fine with a standard spring and carbine buffer but chokes with an H.

 

[Jsp556]

Please don't take this the wrong way. We don't know each other at all. Are you absolutely sure you have the right measurement on that port?

I don't know how it could be that big and not even eject the spent case. Even when mine were quite undersized, they both still at least ejected the cases.

.093 is on the small side for an 18” rg barrel and pretty much the standard port size for a 20”. I remember reading somewhere that the crane barrels are ported at .0995.

 

[Tiribulus]

.093 is on the small side for an 18” rg barrel and pretty much the standard port size for a 20”. I remember reading somewhere that the crane barrels are ported at .0995.

Yeah, but mine were undersized by significantly more than that and still ejected the cases. Maybe it's more sensitive on longer systems.

You made a good point about the AGB. If you drill it out, you can always bring it back down if need be.

 

[KZP]

How far is your gas tube protruding into the upper? Does it end at the cam pin cutout like this one or is it shorter?

 

[Tiribulus]

Not ejecting a spent case can actually be a sign of overgassing. What happens is, your bolt unlocks and begins it's rearward travel before the brass in the chamber has a chance to contract enough to allow extraction as the pressure in the bore is still too high.

Wouldn't that show up on the casing though?

 

[Shoebox]

Please don't take this the wrong way. We don't know each other at all. Are you absolutely sure you have the right measurement on that port?

I don't know how it could be that big and not even eject the spent case. Even when mine were quite undersized, they both still at least ejected the cases.

That was clearly an issue with that particular gas block. With a milspec block, it ran properly on 3 different types of factory ammo (Norma 223 55gr, Win 5.56 55gr, and Win 5.56 62gr green tip) and one of 3 reloads I tried (CFE223 26.4gr ran, H335 22.4-25.2gr would cycle but not hold bolt open, AR Comp 24.0 would unreliably cycle next round, not hold bolt open). All of those would run normally on the original barrel.

 

[Tiribulus]

That sounds just slightly undergassed then at that point with the original gas block. Right on the edge. My BA barrel in the my Aero build was like that. Only failed to lock back some of the time. It has an Aero AGB, but it was opened all the way before I drilled the port.

 

[Shoebox]

Not ejecting a spent case can actually be a sign of overgassing. What happens is, your bolt unlocks and begins it's rearward travel before the brass in the chamber has a chance to contract enough to allow extraction as the pressure in the bore is still too high.

I'm assuming you've tried increasing buffer weight to 5+oz. If you're sure you're not overgassed next step would be at this point since all other attempts have failed will be drilling the gas port. To start off with aim for 0.100" to 0.105"

Not ejecting was definitely the gas block. See previous post. Yes, I tried the Strike (misidentified earlier as Odin) adjustable buffer from 1.75 to 5.6 oz. No change at any weight.

 

[Shoebox]

How far is your gas tube protruding into the upper? Does it end at the cam pin cutout like this one or is it shorter?

Exactly as pictured - all 4 of them.

 

[Shoebox]

.093 is on the small side for an 18” rg barrel and pretty much the standard port size for a 20”. I remember reading somewhere that the crane barrels are ported at .0995.

I'm on the fence whether to send the barrel back to BA or just to order some bits and drill it out myself, bit by bit. (BTW, a 3/32" bit exactly fits in the port.)

 

[Tiribulus]

Just think how great it will be if you fix it yourself

 

[Tiribulus]

We have a great STORE here that has every conceivable little man trinket there is. I got high quality bits for 35 cents apiece. I took my calipers with me and found the exact sizes I needed.

 

[Shoebox]

And if I trash the barrel, I guess a Faxon was meant to be.

 

[Tiribulus]

I hate to look at it this way, but even if something else is the "root cause," throwing some more gas at it may actually still make it run haha.

Although, if I'm keeping all this straight (not a given ) I still bet the port is at the bottom of it all.

 

[Tiribulus]

I have to say. With the first one, when I took it out after drilling the port and it was 100%, it was a great feeling.

I WIN!!! So THERE

 

[Shoebox]

Yeah, that's pretty much all that's left.

 

[Evintos]

Wouldn't that show up on the casing though?

Sometimes. Usually they present themselves as excessive pressure powder loads (extractor marks, ejector marks). Torn case rims are a good indicator. However, sometimes the signs are very subtle. Example - old saved picture from one of my 308 builds (too lazy to dig through my 5.56 folder) and 168gr FGMM.

 

[Evintos]

I'm on the fence whether to send the barrel back to BA or just to order some bits and drill it out myself, bit by bit. (BTW, a 3/32" bit exactly fits in the port.)

IMO, If you have the option to send it back to manufacturer for repair or replacement, that should always be the first option.

 

[Tiribulus]

IMO, If you have the option to send it back to manufacturer for repair or replacement, that should always be the first option.

I totally get this, but I can't stand not fixing stuff myself. Call it a mental quirk. It will haunt me that I probably could have fixed it myself.

 

[Shoebox]

Sometimes. Usually they present themselves as excessive pressure powder loads (extractor marks, ejector marks). Torn case rims are a good indicator. However, sometimes the signs are very subtle. Example - old saved picture from one of my 308 builds (too lazy to dig through my 5.56 folder) and 168gr FGMM.
View attachment 7855588

I will test this week and see if this is the issue. I just assumed with it all the way open it was still under gassed. I'll try factory ammo and close the block a step every 2 rounds and see if anything changes.

 

[Evintos]

And if I trash the barrel, I guess a Faxon was meant to be.

Just be aware, Faxon 18" 5.56 (rifle length gas) are drilled to 0.093"

 

[TonyTheTiger]

And if I trash the barrel, I guess a Faxon was meant to be.

FWIW, I've never seen a Faxon barrel that shot particularly well.

 

[Shoebox]

Just be aware, Faxon 18" 5.56 (rifle length gas) are drilled to 0.093"

Well all this would probably be moot if I hadn't been cheap to start with. I'd wanted a 20" barrel, but JoeBobs had a great deal on these 18"

So if I replace it it'll be a 20"

 

[Shoebox]

FWIW, I've never seen a Faxon barrel that shot particularly well.

Good to know, I'd read good things about them overall.

 

[r.tenorio671]

I will test this week and see if this is the issue. I just assumed with it all the way open it was still under gassed. I'll try factory ammo and close the block a step every 2 rounds and see if anything changes.

....if the AGB you are using is the "detent" type, you can save some ammo by using the procedure of (1) AGB Closed, 1 round in mag, fire, check for lock back. (2) If no lock back, adjust AGB 1 click out, 1 round in mag, fire, check for lock back. Repeat until lock back achieved. Once achieved, load 2 rounds in mag, fire to confirm cycling is good and feeds 2nd round and locks back after 2nd round is fired. If not feeding 2nd round, open AGB 1 click, repeat sequence until cycling, feeding * firing of 2nd round and lock back are achieved. Once achieved, open AGB 1 more click for reliability and test with no less than 5 rounds in mag.

...you want to test with your "weakest" ammo, then validate with your "hottest" ammo, adjusting your settings to reliably function with BOTH without having to make adjustments when swapping between the weakest & hottest and any in between loads. Unless your weakest ammo is significantly "weaker", there most likely will be a setting on your AGB that will function reliably for both. This procedure applies to ANY brand of barrel.

 

[Shoebox]

@r.tenorio671 you are awfully optimistic about this thing. I am 99.5% sure it's undergassed, and starting with the AGB closed will be a waste of ammo. I need to start fully open and close it a click at a time to see if by some miracle it's overgassed. I am almost certain there is no setting on the AGB that will let it run properly.

With the milspec block it would only run normally on the hottest ammo, wouldn't lock back on anything else, and would not cycle the next round about 10% of the time on others.

 

[r.tenorio671]

@r.tenorio671 you are awfully optimistic about this thing. I am 99.5% sure it's undergassed, and starting with the AGB closed will be a waste of ammo. I need to start fully open and close it a click at a time to see if by some miracle it's overgassed. I am almost certain there is no setting on the AGB that will let it run properly.

With the milspec block it would only run normally on the hottest ammo, wouldn't lock back on anything else, and would not cycle the next round about 10% of the time on others.

....just trying to contribute relevant info, it's up to you if you wish to use it. Keep in mind, an over-gassed system can also exhibit the same symptoms of an under-gassed system, i.e., the BCG out-racing the magazines feeding and activating the bolt catch speed. Good luck on your efforts.