AR-15 Help Needed: Failure to Feed

[Phil3]

I am at wits end trying to understand why my home built AR-15 has begun to often fail to feed (FTF) the next round. This happens about 20% of the time, no matter if it is a C-Products mag, MagPul P-Mag (in either 10 or 20/10 capacity). Two kinds of incidents are happening.

1) With rounds still left in the mag, pull the trigger and a light click only. Pull the charging handle back, and no round in the chamber. Pull charging handle back while simultaneously latching the bolt, and then hit bolt release to pick up the previously non-chambered round. Chambers OK and fires fine.

2) Round jams on it ways into the chamber. The bolt rides up on the case, denting it in one or two places from bolt lugs, just behind case neck. Drop mag, round falls out.

3) I think only once did the gun fail to lock the bolt back on the last round. It normally performs OK in this regard.

The rifle has previously fired hundreds of rounds of factory ammo without incident. It has started this with my reloads. Thinking those loads were too light to reliably operate the gas system and bolt, I kept creeping up in loads, but the FTF keeps happening. Even with 23.6 grains of Vhitavouri N133 behind a 53 grain bullet. Perhaps the N133 (and the Hodgdon H322 which does the same thing) are just too fast burning. But, quite a few others have told me these powders work fine for them. ???

I took the gun apart and found gas leakage at the joint between gas tube and gas block. Normal? The bolt is a mess. Too much lubricant? I can't enjoyable shoot the gun as I can not make it through 5 rounds without having to clear a FTF or jam. Extraction and ejection are 100% reliable. Barrel is 22" long. Distance from front of receiver to gas port is 12-15/16". Gas port diameter .092" with a bit of a loose fit using smooth end of drill bit. Gas block is JP Rifles non-adjustable.

Ideas? Pics below.

Phil


Looks like a fair amount of leakage between gas block and gas tube, shooting gases down top of barrel. That looks like erosion of top of the barrel but it is carbon. I can pick it off.


Note black deposits from gas block/tube leakage.


Note black deposits from gas block/tube leakage.


Gas tube end that fits into bolt carrier.


Young Manufacturing Match bolt.


Young Manufacturing Match bolt.


Young Manufacturing Match bolt.


Young Manufacturing Match bolt.

Phil

 

[BigDMT]

Not sure. Just gonna throw this out there...

Might want to seat your bullets deeper. Check your hand loads next to a factory round and make sure the bullets are not seated out further than that. A bullet seated out too far can cause the front of the round to lift too early from the magazine, or can jam the bullet when trying to enter the chamber.

AND...
When is the last time you took your BCG completely apart for a very thorough cleaning?

 

[Klong]

How many rounds have been fired with the bolt and bolt carrier? What was the factory ammo?
What is the barrel length?
Any lube in the buffer area?
Do you have a different CCG to try?

 

[jonbearman]

That bolt carrier assy is filthy and needs real cleaning,and who's 53 grain bullet are you using and seating depth in an autoloader is key to smooth operation. I would also make sure you clean that barrel and extension very carefully. Regarding the gas block leakage,it is common and even pinned blocks leak some.Just clean the od of the barrel and gas tube up nice and clean.The bolt carriers do like to be wet than dry.Some large hollowpoints will catch the edge of the barrel if seated out to far.

 

[Phil3]

I don't know how to quote multiple replies in my own single reply (if even possible), so will copy and paste responses below with my answers.

“When is the last time you took your BCG completely apart for a very thorough cleaning”?
Immediately prior to this last shooting trip. The entire bolt and carrier assembly was completely disassembled (except for gas ring removal), cleaned with solvent and brushes, then cleaned in an ultrasonic cleaner, and then dried with compressed air. The bolt and carrier assembly got the way they look after 40 rounds.

“How many rounds have been fired with the bolt and bolt carrier? What was the factory ammo”?
Approximately 500.
223 Remington -PMC Bronze 55 grain FMJ. Blackhills 55 grain. Neither gave problems. Blackhills showed signs of over pressure.

“What is the barrel length”?
22”

“Any lube in the buffer area”?
No.

“Do you have a different CCG to try”?
“CCG” Not sure what that is. I don’t have another bolt carrier group (BCG) if that is what you mean.

“That bolt carrier assy is filthy and needs real cleaning,and who's 53 grain bullet are you using and seating depth in an autoloader is key to smooth operation. I would also make sure you clean that barrel and extension very carefully. Regarding the gas block leakage,it is common and even pinned blocks leak some.Just clean the od of the barrel and gas tube up nice and clean.The bolt carriers do like to be wet than dry.Some large hollowpoints will catch the edge of the barrel if seated out to far”.

The bolt carrier group was white glove clean before I shot the 40 rounds that left it as you see it. The bullet is a Sierra MatchKing 53 grain flat base. The loaded length for all rounds has been mag length, or 2.250”. The barrel was inspected with a bore scope before the 40 rounds were fired, and it was quite clean. The extension is harder to clean, but yes, it could probably use better cleaning.

Phil

 

[BigDMT]

Mag length seating would be wrong. But 2.250" OAL should work. Could seat it down another .005" to .010" and try it. Perhaps make sure you bump the shoulders back to factory ammo specs as well. Or at least as far as your die will allow if you cant get that far.

another thought...
if its not any of that, check to make sure your buffer travels freely in the tube and that the port hole on the end of the tube is not plugged up with something.

 

[Phil3]

Mag length seating would be wrong.

I am not sure what you mean. ???

But 2.250" OAL should work.

From what I can find, 2.260" is maximum mag length. I used OALs according to reloading manuals, specifically the Sierra manual for the AR-15.

Could seat it down another .005" to .010" and try it. Perhaps make sure you bump the shoulders back to factory ammo specs as well. Or at least as far as your die will allow if you cant get that far.

This ammo was loaded using new Winchester cases, so the shoulders were pretty far back.

another thought...
if its not any of that, check to make sure your buffer travels freely in the tube and that the port hole on the end of the tube is not plugged up with something.

I just had all this apart, and not sure what you are referring to about a port hole on the end of the tube (buffer tube?). My buffer tube has a solid end with a configuration to allow a wrench to tighten it, and a spacer that goes behind it. Prior to taking it apart, the bolt retracts to a point that it is supposed to, indicating there is nothing preventing full travel.

By the way, thanks for your helpful suggestions, even if they are ruling out things and narrowing possibilities.

Phil

 

[BigDMT]

the fact that you took the BCG apart right before this issue has me wondering as well.....

with the BCG in your hands, you should be able to easily push the bolt head into the carrier, then swing it down really fast in a chopping motion (like swinging a hatchet) and it should fully deploy. Can it do that?

if the bolt head is not moving freely in the carrier, it can cause some feeding havoc.

 

[jonbearman]

The screw that bolts through the end of the buffer tube should have a hole drilled all the way through,otherwise when the buffer slides back it creates compressed air and feeding would be near to impossible if there was no where for the air to vent. This would be the upper screw in the butt stock.I too have had troubles with hollow points but not the ones you are using. The vmax or any tipped bullet would be a better choice for flawless feeding in my opinion.I would try a cleaner powder like h335 or blc-2 or something to take the sooting out of the equation.

 

[Phil3]

the fact that you took the BCG apart right before this issue has me wondering as well.....

with the BCG in your hands, you should be able to easily push the bolt head into the carrier, then swing it down really fast in a chopping motion (like swinging a hatchet) and it should fully deploy. Can it do that?

if the bolt head is not moving freely in the carrier, it can cause some feeding havoc.

I've taken the bolt carrier group apart innumerable times, and am confident it is together properly. The bolt head goes into the carrier with light finger pressure. And if I swing it, the bolt fully deploys. I don't have to swing really hard for this to happen.

Phil

 

[Phil3]

The screw that bolts through the end of the buffer tube should have a hole drilled all the way through,otherwise when the buffer slides back it creates compressed air and feeding would be near to impossible if there was no where for the air to vent. This would be the upper screw in the butt stock.I too have had troubles with hollow points but not the ones you are using. The vmax or any tipped bullet would be a better choice for flawless feeding in my opinion.I would try a cleaner powder like h335 or blc-2 or something to take the sooting out of the equation.

Yes, there is a hole in the rear screw. The N133 powder I am using is reputedly quite clean, and does appear cleaner than the H322. H335 is supposed to be really good and will try that, once I can find any.

Phil

 

[Phil3]

Now I found something interesting, and near impossible to believe. I pulled off the gas block and gas tube, as an assembly. I did this because I noticed some carbon buildup near the gas block/tube junction. See the photos. I tried blowing through the gas tube (from bolt carrier end). Very difficult to do. I didn't think it ought to be that hard. It was like I was hardly making any air flow. The gas tube was aligned properly in the gas block. I poured some gun solvent down the tube and let it sit a few minutes. Some ran out the other end fairly quickly, making me wonder if I imagined how hard it was to blow through the tube/block assembly. I ran a coat hanger down the tube about 6", until I got to the kink in the tube. I then blew it out with compressed air. Tried blowing through it again, and it seemed MUCH freer flowing.

I hard time believing the gas tube or block was blocked. Not with thousands of pounds of pressure blowing through the tube. I can't find anything else functionally wrong with the gun. I may just have to take it to the range and try it and see what happens. But, if it works fine, how in the heck can a gas tube become plugged or partially obstructed?

Phil

 

[Beau]

N133 is too fast for some guns.

Go to a slower powder like Varget, Re15, TAC, etc.

Oh, and gas tubes do get blocked. Don't use Wipe-out to clean your barrel. Change tubes every time you rebarrel and surely not less than every other time.

Check the gas key end of the tube for wear too.

 

[jonbearman]

They make extra long pipe cleaners for doing just this(sinclairs) and some powders as I made reference earlier are way dirtier than others.I would switch to something different like h335 or blc-2 or 748 or whatever to avoid the excess soot. If you shot it with oil in the barrel it will force minute amounts down the gas tube and start the process of gooping the tube up. Soak the tube in a good bore cleaner and run the pipe cleaner down to dislodge what will come off.

 

[chuckbuster243]

Another thing you can check to see if you are getting a full cycle. Put one round in the chamber and a empty mag in the well. Fire the one round and the bolt should lock back if it has enough gas. If not you have either to light of load or gas obstruction. If it does, it is something with the ammo itself not wanting to feed. Which these guys have already spoken of. Matt

 

[rcw3]

Phil3

IMO - addressing your issues - the gas port is marginal (i.e. as in too small) for an N133 load with light bullets. The pressure curve on N133 drops off fast and light bullets compounds the problem. The factory ammo you say cycles fine, but your hand loads with N133 and light bullets do not cycle enough in some cases for the bolt to get back far enough to pick up the next round out of the magazine (i.e. hence why you pull the trigger, hear the click of the hammer falling and then there's nothing in the chamber). N133 was never a powder considered for the porting of AR-15's (and most AR barrels are not set up with porting for such powder with lighter bullets) and if you are going to run it (and no reason why you cannot) you will likely need to open the port another .005" in dia. (i.e. try .098 or thereabouts).

You point #2 is also a porting symptom caused by the bolt not cycling far enough back on the case but then nudging it forward into a jam (i.e. because it never got all the way back beyond the back of the case to pick it up firmly to push it forward).

Your point #3 - a marginally cycling action may still lock back on the last round because there is less friction on the carrier when the magazine is empty and the last round is in the chamber and it cycles back fine on an empty magazine.

Robert

 

[racesnake]

Failure to feed is because your BCG is not coming back far enough to pickup a round from the mag. Scrape carbon from inside the bolt carrier bore, check that bolt key is not clogged, replace gas rings on the bolt (be sure to align gas rings properly) and look for stoppages in rest of gas system. One other thing - be sure buffer is not binding - lube it and the outside of the BC. Should fix the problem.

 

[Phil3]

Phil3

IMO - addressing your issues - the gas port is marginal (i.e. as in too small) for an N133 load with light bullets. The pressure curve on N133 drops off fast and light bullets compounds the problem. The factory ammo you say cycles fine, but your hand loads with N133 and light bullets do not cycle enough in some cases for the bolt to get back far enough to pick up the next round out of the magazine (i.e. hence why you pull the trigger, hear the click of the hammer falling and then there's nothing in the chamber). N133 was never a powder considered for the porting of AR-15's (and most AR barrels are not set up with porting for such powder with lighter bullets) and if you are going to run it (and no reason why you cannot) you will likely need to open the port another .005" in dia. (i.e. try .098 or thereabouts).

You point #2 is also a porting symptom caused by the bolt not cycling far enough back on the case but then nudging it forward into a jam (i.e. because it never got all the way back beyond the back of the case to pick it up firmly to push it forward).

Your point #3 - a marginally cycling action may still lock back on the last round because there is less friction on the carrier when the magazine is empty and the last round is in the chamber and it cycles back fine on an empty magazine.

Robert

Robert,

Thanks so much for this response.

I went with the N133 and light bullet as it was the "accuracy load" in the Sierra manual for the AR-15. But, their barrel was 2" longer than mine, and who knows what port size was used. I think I would rather run a powder that is more suitable for the port I have now. I have four powders on hand. In order from fastest to slowest according to the Hodgdon site, and their numerical rank (out of 145 powders):

Hodgdon H322 (#74)
Vhitavouri N133 (#79)
Alliant Reloder 15 (#97)
Hodgdon Varget (#99)

Depending on source, the N133 and H322, may swap positions.

With a 1:9 twist barrel, I am generally shooting 52 to a max of 69 grains (not tried those yet). Do you have any recommendations on a proper powder that would be a good start and has a reputation for working well in ARs with my barrel length? Would the Reloder15 and/or Varget work well with light bullets? I have 52, 53, 55, 68, and 69 grain bullets on hand. Do you think the fast burning powder and short stroking would negatively affect accuracy? It surely interrupted my shooting concentration, but wondering how accuracy is affected.

Thank you.

Phil

 

[jonbearman]

Is the barrel torque ok,in another words does the barrel have any play if you try to move it and looking at the barrel nut. I have seen a few loosen slightly and cause problems that is the barrel extension.

 

[JeffinTX]

fairly standard high power shooters' load with what you have on hand would be 25grn of Varget/RL15 with the 68/69 bullets. Seat them 2.255". If you gun can't shoot this well, it has bigger problems.