AR-15 Failures to Feed - Dirty Bolt/Carrier

[Mark K]

Searched, but to my surprise didn't find anything.

I took my pretty-new AR-15 out to the Marriottsville range yesterday, trying to burn through some ammunition before we move in a couple months.

After about 250 or 300 at times rapid rounds, it started getting regular failure-to-feed problems. The bolt would catch the next round in the mag, but the tip of the bullet would get hung up on the respective feed ramp.

Cycling the bolt and blot carrier, there was a horrible amount of almost gritty friction. I could barely pull back the charging handle at times. So that was obviously the problem -- the bolt wasn't riding forward with enough force to feed the rounds.

The rifle was cleaned the last time I had it on the range, but I had my daughter out that time for her first time shooting the AR, and I think she's the one who cleaned it rather than me -- she may not have realized how gunked up AR bolts and bolt carriers can get, and I didn't "inspect" the rifle closely enough afterward.

Still, I wouldn't expect that sort of problem after any kind of cleaning, after only a couple hundred rounds...?

 

[Pinecone]

How much lube?

Extra lube helps the gunk migrate out of the areas where it can cause problems.

 

[BradMacc82]

For one, if the round is getting hung up on the barrel extension/receiver feed ramp cuts - You have a "clicker", basically the transition from receiver cut to barrel extension ramp isn't smooth, giving a spot for the round to catch/hang-up during feeding.

A blending/polish will alleviate that.

After only 250/300 rounds, the bolt/carrier shouldn't be dirty enough to affect operation - unless you were running steel-cased rounds suppressed. I've had range days that were 1k to 1500 rounds, and aside from the rifle getting uncomfortably warm, no operational issues arose.

Type of ammo, and some specifics on your upper would help any possible diagnosis.

 

[Mark K]

How much lube?

I generally use CLP, leaving a thin coating on the parts.

For one, if the round is getting hung up on the barrel extension/receiver feed ramp cuts - You have a "clicker", basically the transition from receiver cut to barrel extension ramp isn't smooth, giving a spot for the round to catch/hang-up during feeding.

[...]

Type of ammo, and some specifics on your upper would help any possible diagnosis.

It's a Del-Ton upper, and there's an Anchor Harvey mark on the right side between the charging handle and the brass deflector.

I was using mostly American Eagle 55 gr FMJ. Some miscellaneous stuff too, but all FMJ rounds with brass cases.

The reason why I think it's a bolt/carrier problem is the amount of friction I was feeling pulling back the charging handle. And the bolt carrier wasn't slamming forward as fast as should, either, even when it was chambering a round.

I'm a retired Army officer, and am at least somewhat familiar with M16s/M4s. I've never felt a bolt/carrier move with so much difficulty.

There was a lot of black sludge on the bolt and carrier when I was cleaning the rifle last night. And a lot of rock-hard carbon build-up on the bolt, particularly just behind the gas rings.

Now that everything is cleaned and CLP-ed, it all feels fine...

Now that you mention it, I can feel a bit of a "catch" or edge in the (M4) feed ramps, where the barrel extension meets the upper receiver. I suppose that doesn't help things, and it would probably be worth getting polished. But I still think the bolt/carrier's friction was causing the problem... it was really, really bad...

 

[clandestine]

I generally use CLP, leaving a thin coating on the parts.

NO. Use more lube. CLP is fine but it tends to evaporate if you store the gun. It also tends to cook or shed lube due to the viscocity. IMHO use a heavier lube. If you don't want to break the bank use Syn Motor Oil.

It's a Del-Ton upper, and there's an Anchor Harvey mark on the right side between the charging handle and the brass deflector.

I was using mostly American Eagle 55 gr FMJ. Some miscellaneous stuff too, but all FMJ rounds with brass cases.

The reason why I think it's a bolt/carrier problem is the amount of friction I was feeling pulling back the charging handle. And the bolt carrier wasn't slamming forward as fast as should, either, even when it was chambering a round.

The gun could be undergassed slightly. Youll notice that when a gun gets fouled or isn't lubed well. What weight Buffer is in it? If its a H or heavier remove it and install a standard Carbine Buffer. If the Recoil Spring is a XP one remove it and install a Colt Buffer Spring, or a Shrome Silicone Superior Shooting Solutions Flat Wire Spring.

I'm a retired Army officer, and am at least somewhat familiar with M16s/M4s. I've never felt a bolt/carrier move with so much difficulty.

There was a lot of black sludge on the bolt and carrier when I was cleaning the rifle last night. And a lot of rock-hard carbon build-up on the bolt, particularly just behind the gas rings.

Sludge means nothing. Add lube and it will be fine. It dosent have to be clean, just lubed. The U.S. Military is obsessed with clean weapons and it does not matter.

Now that everything is cleaned and CLP-ed, it all feels fine.

This confirms nothing is wrong with the Upper but does not mean the buffer or spring isn't too heavy.

Now that you mention it, I can feel a bit of a "catch" or edge in the (M4) feed ramps, where the barrel extension meets the upper receiver. I suppose that doesn't help things, and it would probably be worth getting polished. But I still think the bolt/carrier's friction was causing the problem... it was really, really bad...

That's a clicker then as Bradmacc said. The barrel has to be removed to fix that. Polishing wont help, the steel barrel extension ramps have to be moved forward between .020-.040 and then polished. If you remove the anodizing from the aluminum ramps in the upper it will wear rapidly because the anodizing hardens the surface.

 

[Mark K]

IMHO use a heavier lube.

Like what, other than synthetic motor oil?

It had been about a month since I'd shot the rifle previously. You think the CLP evaporating would have caused the bolt/carrier friction after a bunch of rounds?

What weight Buffer is in it? If its a H or heavier remove it and install a standard Carbine Buffer. If the Recoil Spring is a XP one remove it and install a Colt Buffer Spring, or a Shrome Silicone Superior Shooting Solutions Flat Wire Spring.

The buffer is stamped with an "H." Too heavy, you think? What's the "H" buffer designed for?

I have no idea what kind of recoil spring it is. It's got 38 coils, if that means anything...

That's a clicker then as Bradmacc said. The barrel has to be removed to fix that. Polishing wont help, the steel barrel extension ramps have to be moved forward between .020-.040 and then polished. If you remove the anodizing from the aluminum ramps in the upper it will wear rapidly because the anodizing hardens the surface.

Scott's Gunsmithing in Glen Burnie isn't too far away. I assume you'd recommend them?

 

[clandestine]

Like what, other than synthetic motor oil?

It had been about a month since I'd shot the rifle previously. You think the CLP evaporating would have caused the bolt/carrier friction after a bunch of rounds?

It probably evaporated. Just be sure to relube before use again if you want to stick with CLP.

I use Motor Oil, but if you want gun lube stuff like Slip 2000 works well.

The buffer is stamped with an "H." Too heavy, you think? What's the "H" buffer designed for?

I have no idea what kind of recoil spring it is. It's got 38 coils, if that means anything...

H Buffer is normally the "Standard" fir a carbine, but this assumes the gun is gassed correctly, but this gun sounds undergassed which means the H Buffer is just slightly too heavy. I suggest buying a standard one (They are unmarked and are cheap and only cost $7.00-$15.00).

Scott's Gunsmithing in Glen Burnie isn't too far away. I assume you'd recommend them?

Normally yes, but he I not taking any work at the moment. I wont be back there till January if Im lucky.

 

[Mark K]

I wont be back there till January if Im lucky.

But they're still there, and taking work, right?

I'll just tell them you recommended them.

Undergassed, eh? Did I mention how gritty and hard the bolt/carrier was to cycle by hand?

 

[clandestine]

But they're still there, and taking work, right?

I'll just tell them you recommended them.

Undergassed, eh? Did I mention how gritty and hard the bolt/carrier was to cycle by hand?

Scott isn't taking work now. He severely backlogged.

The gun should run when its fouled. If it wont its either a lube problem, ammo problem, the gun is overbuffered or undergassed. Best bet is to lube better next time and get a lighter buffer. My AR's will run after throwing sand on an open dust cover, yours should too.

If you still have a problem switch lubes.

If you still have a problem after switching lubes, I would look into the gun leaking gas, or perhaps the BCG is just not up to par. The Gas Port can be opened in the barrel but that's a LAST resort.

Don't cut coils on the buffer spring.

 

[Mark K]

Scott isn't taking work now. He severely backlogged.

Ah, that sucks.

Good for him. Sucks for us.

I've removed the upper, and I'm running the bullet tip of a cartridge held lightly in my fingers up both feed rams. While I can slightly feel when the bullet tip runs over the junction between the receiver and the barrel extension, it doesn't hang the bullet up at all. So maybe it's not the feed ramps.

So my next thing to try will be to lube the bolt carrier better... What area(s) should I pay particular attention to?

 

[smokey]

What wear marks are you seeing on the bolt carrier and in the upper receiver? With everything cleaned, snap a picture of the barrel extension(feed ramps), the inside of the upper(with BCG removed), and the BCG itself from the top and bottom. Toss them up here and the gun-nerds can just take a glance at if anything looks odd.

You should be using much more lube. Aside from protecting the parts from premature wear and reducing friction, the lubes will also migrate carbon and keep fouling from building up too much. A lot of people will just keep a bottle nearby and when the gun starts slowing down, they'll dump it into the bolt through the holes until things run slick again. How are your gas rings? If you yank your BCG, pull the bolt all the way out, and stand it on the bolt-face, does it compress back in under its own weight or stay extended?

Oh, and a feed issue...what mags are you using. That's a pretty important component to a semi-auto working correctly. Pmags, troy battlemags, and lancers all seem to be solid in 30 rnd'ers. Larue just came out with their gay-pride hexmags if you prefer more colors.

 

[clandestine]

Here is how I lube an AR:

I use Synthetic Wheel Bearing Grease on the Charging Handle Stem, Cam Pin, and the 4 raised Carrier Rails. A dab of grease about the size of mentos mint is enough grease to do all of the above.

Then I dip the assembled Bolt Carrier Group into Synthetic Motor Oil up to the Firing Pin Retaining Pin and insert it into the weapon. Cycle it a few times and the oil/grease will migrate to where it needs to be and your set.

 

[bkuether]

Here is how I lube an AR:

I use Synthetic Wheel Bearing Grease on the Charging Handle Stem, Cam Pin, and the 4 raised Carrier Rails. A dab of grease about the size of mentos mint is enough grease to do all of the above.

Then I dip the assembled Bolt Carrier Group into Synthetic Motor Oil up to the Firing Pin Retaining Pin and insert it into the weapon. Cycle it a few times and the oil/grease will migrate to where it needs to be and your set.

And ever since I changed to this method nothing has ever gone wrong with any of my ARs. I was using light oil. My internals were starting to wear. You need heavy oil. Listen to Clandestine.

 

[clandestine]

And ever since I changed to this method nothing has ever gone wrong with any of my ARs. I was using light oil. My internals were starting to wear. You need heavy oil. Listen to Clandestine.

Im glad you have seen an improvement. Its why I post in tech threads, to help. Thanks my friend.

If people choose not to listen its their choice and their firearm. I just hope it dosent fail if they have to use if for defense.

 

[DaemonAssassin]

Well hell. Chad taught me something new. Thanks Chad!!!

 

[baltech]

Thanks for the information chad.

 

[ThawMyTongue]

Due to recommendations from Chad I bought a gallon of syn motor oil which happened to have an opening large enough to slip the BCG into and a travel shampoo container of the oil in my range bag. I run 'em wet and have not had an issue.

 

[engineerbrian]

And ever since I changed to this method nothing has ever gone wrong with any of my ARs. I was using light oil. My internals were starting to wear. You need heavy oil. Listen to Clandestine.

Same here. My AR's were jam o matics until i started using this method too. Havent had a problem since

 

[bigb201]

Any particular viscosity on the motor oil?

 

[Mark K]

I'm back.

Yeah, I'm learning quite a bit here, too. Thanks from me too, Chad.

It's really a cultural thing... I've always learned (I'm sure from the Army, since it's from so long ago) that weapons parts should only have a light coating or sheen of lubricant, in order not to attract dirt and gunk.

That's obviously not appropriate with an AR bolt and carrier. The lubricant obviously dried out on me, and that's what caused the cycling problems. I'll lube it all up next time I go to the range, and see how it works.

What wear marks are you seeing on the bolt carrier and in the upper receiver? With everything cleaned, snap a picture of the barrel extension(feed ramps), the inside of the upper(with BCG removed), and the BCG itself from the top and bottom. Toss them up here and the gun-nerds can just take a glance at if anything looks odd.

OK, let's see if this works:











The only wear I'm seeing on the bolt carrier, other than on the bottom from the hammer being cocked back, is at the front and rear ends of the four "rails."

How are your gas rings? If you yank your BCG, pull the bolt all the way out, and stand it on the bolt-face, does it compress back in under its own weight or stay extended?

I think the gas rings are fine...

Oh, and a feed issue...what mags are you using.

I was using Brownells aluminum 20- and 30-round mags -- five of each; the 30-round mags were brand-new. I was having the feeding problems with all of them at the end.