Case Head Gouging on Bushmaster AR

[ZigZagZeke]

OK, so this Bushmaster Varminter has a Fulton Armory stainless bull barrel. It's fitted with the FA .936" gas block with a rifle length tube. The gas block is well aligned and sits just outside the hand guard. The rifle runs just fine. The issue is the ejector pin seems to be smearing the brass on the case head upon ejection. There are curved scratches on the case heads where the ejector pin would contact the head. Looks like it's caused by the ejector pin as the bolt rotates open to eject the spent casing. The scratches don't happen if the action is cycled without firing.

My best guess is that the BCG is getting too much gas pressure too soon and the case is being extracted before the pressure in the case has fully subsided. Thus, the case can't rotate in the chamber along with the bolt, and the ejector pin is being dragged around the circumference of the case head, causing these scratches. Naturally, I'd like to do something to remedy this just because it shouldn't be happening, but I have a feeling that it is also unsafe, and may also be affecting accuracy. The headspace has been checked, and it's on the tight end of normal, but it's within specs.

I've ordered a Wilson Combat adjustable gas block that will allow me to tune how much pressure the BCG sees, and how soon it sees it. That's my best thinking on the issue. Anybody got any other ideas or comments?

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[Velzey]

Take the ejector out of the bolt head and flat file .005 - .010 off of it, reinstall and test fire.

Helps to use a small vee block and clamp. But you can do it by eye also in a regular vise.

 

[bellarum]

Can you post a picture of your brass?

 

[ZigZagZeke]

Take the ejector out of the bolt head and flat file .005 - .010 off of it, reinstall and test fire.

Helps to use a small vee block and clamp. But you can do it by eye also in a regular vise.

That is the other possibility I was contemplating, that maybe the ejector pin is too long and is bottoming on the spring or something like that.

 

[ZigZagZeke]

Can you post a picture of your brass?

It's very hard to see in these pictures. These are .223 casings. It's more pronounced on the 5.56 casings, where it actually leaves a burr on the edge of the case, but I can't find any of those. The best examples here are the third from the left casing in the second picture, and the second from the left in the third picture. Click on them to see the full size pictures.

 

[ZigZagZeke]

I just noticed that I left out that this is a 24" barrel.

 

[bellarum]

I have some that look exactly like that. I recently upgraded my bolt with a new extractor and rings from BCM. It still happens. Makes them a PIA to get in and out of the shell holder when reloading.

 

[Rick4070]

Just out of curiosity, Zeke, what is you rifle chambered for, .223 Rem., or 5.56mm?
I ask, because if your rifle is chambered for.223, and you are firing 5.56 out of it, might that be part of the problem?
Oh, and I must admit that I don't know what FA chambers their rifles in, nor if it would make any difference at all, just throwing an idea out there....

 

[ZigZagZeke]

Just out of curiosity, Zeke, what is you rifle chambered for, .223 Rem., or 5.56mm?
I ask, because if your rifle is chambered for.223, and you are firing 5.56 out of it, might that be part of the problem?
Oh, and I must admit that I don't know what FA chambers their rifles in, nor if it would make any difference at all, just throwing an idea out there....

Fulton Armory barrels (at least this model) are marked .223/5.56. Here's what Fulton Armory has to say about it:

Fulton Armory uses a "5.56 Match" chambering in its rifles/uppers/barrels (in fact our barrels are marked as such), which is a slightly modified SAAMI chamber with a tad longer throat to accommodate NATO bullets. The Fulton Armory 5.56 Match chamber allows for the safe and reliable use of all SAAMI and NATO ammo, while offering the accuracy potential of the SAAMI chamberings with match commercial cartridges. Remember, there's often a large difference between bolt guns and military rifles. This is particularly true for the 5.56 vs .223; Fulton Armory is well known for the finest performance for any given platform, and our 5.56 Match chamber is one way we achieve that performance with the AR-15-type rifle.

 

[Rick4070]

Interesting, and it seems that you can safely fire both in a FA barrel, but I wonder why the marks are more pronounced on the 5.56 cases..
Have you tried pushing in on the ejector to see if it will push in farther than than the bolt face?
You mentioned that you thought the ejector might be too long, or bottoming out???
(Just another thought....)

 

[civilian75]

I have another theory. Could this be extractor marks, instead, caused by the same mechanism? Try twisting a clean empty case head against the bolt face, manually, as hard as you can. Make sure you add a mark somewhere to track alignment.

Also, I noticed one of the shells actually shows evidence of an extruded extractor (half moon)! Was all of this factory ammo?

If you could retake the pics, it'd be great. Force the lens to focus on case heads, not your fingers.

 

[ZigZagZeke]

I have another theory. Could this be extractor marks, instead, caused by the same mechanism? Try twisting a clean empty case head against the bolt face, manually, as hard as you can. Make sure you add a mark somewhere to track alignment.

Also, I noticed one of the shells actually shows evidence of an extruded extractor (half moon)! Was all of this factory ammo?

If you could retake the pics, it'd be great. Force the lens to focus on case heads, not your fingers.

What is an "extruded extractor (half moon)"?

And BTW, I believe the 5.56 are a slightly hotter load. If so that would make the condition worse.

Here are some slightly better pics. All the damage is at about the 1:00 o'clock position. Click on the pictures to enlarge them:

 

[ZigZagZeke]

OK, what I find in the extractor spring location is a spring and a small silicone cylinder/pad inside the spring. In the picture below of an extractor upgrade kit, it shows the spring and the blue rubber cylinder that was in mine. Mine did NOT have the O-ring though. Should the silicone piece be there? Mine looks like it's damaged. It's got a cut in it, and I think that one of the spring coils was caught in the cut, effectively increasing the spring rate of the spring, just like a spring rubber does in a NASCAR race car.



Is there somebody near Portland who sells these parts? I'd like to get some new parts before Saturday. I know that they make kits that include the extractor, spring, and silicone rubber pad. Should I, or could I just take out the silicone piece and go without it?

 

[ZigZagZeke]

OK, so I went to Curt's today and bought a new extractor and spring. Trouble is it won't fit my bolt. It's too wide and the pin hole is too big. The locking lug on the outside of it is a lot bigger too. What did they give me? I specified that it was for a Bushmaster AR. I guess I'll have to go back and take my bolt with me this time.

 

[Velzey]

Sounds like they gave you one for a .308 bolt!

 

[ZigZagZeke]

Yep, sounds like it. But the good news is that after the Memaloose cleanup today, I and a couple of other NWFA people stopped at Helion pit and shot a few rounds. My Bushmaster with the new extractor spring and buffer left almost no marks at all on the case heads. Looks like that one is laid to rest now.

 

[bellarum]

Did you remove the o ring?

 

[balline36m3]

I'm having the same problem on a upper build I just finished. What all did you change?

 

[ZigZagZeke]

I'm having the same problem on a upper build I just finished. What all did you change?

Did you remove the o ring?

If you scroll up and look at the picture above of the extractor kit, what was there originally was the spring and the little blue cylindrical buffer that goes inside the spring. My buffer had a cut in it, and one of the spring coils seemed to be hung up in the cut. There was no O-ring in mine. I replaced the spring and blue buffer pad inside the spring. That seems to have just about eliminated any marks, even on the 5.56 cases.

 

[bellarum]

Nice! I'm going to remove the o-ring and see how mine runs next time I go out.