6mmAR Problem.

Cory Lee

Cory Lee

Sergeant
Full Member
Minuteman
Apr 1, 2008
299
1
DFW
#1
This is a new AR build. I have built several in the past with no functioning problems at all. This is also my first time loading this caliber. I have also loaded several other calibers in the past with no problems at all.

This is a 6mmAR-P. Its a 243lbc from ar15performance.com. A 6.5Grendel necked down to 6mm. 243lbc is to 6mmAR as 264lbc is to 6.5Grendel.(The neck diameter & throat angle are slightly different but are interchangeable.) I bought both the 6mmAR-P barrel and his superbolt to match the headspacing.

I used the 6PPC dies held them .070" above the shell plate to resize and neck down the Grendel brass.

I loaded 20 rounds working up to 28.4gr of H4895 and loaded the 195SMK to 2.295". (Mag length for the Grendel magazines) I found this from the guy running ar15performance.com on another forum. I think it was beyond556.com. He goes by the name Constructor and was selling some barrels there. Claimed he was getting 2900fps out of this barrel and load.

Anyway, when I go to chamber the first round, it won't chamber and I can't pull the charging handle back.(Charging handle is still 1/2" from latching shut.) I had to use a screw driver to pry the bolt carrier back.

The bolt cycles fine when the gun is empty. When I push an empty case into the chamber and slam the bolt onto it, it closes but I can only pull the charging handle back about 1/2". Probably 1/2 of the time the bolt didn't catch the case and I had push it out with a cleaning rod. I loaded up a dummy round and it did the same thing several times. It did it when loading from the magazine or when pushing it into the chamber by hand. I tried seating the bullet .010 deeper but same results.

There are no marking on the cases. From what I can see the chamber looks ok. I double checked the bolt installation and everything is good there. The barrel nut is torqued to spec.

I think the problem is with the bolt, but could be in the chamber? Any help? I'm emailing him as well.




 
#2
I shoot a grendel and coal is all over the place depending on bullet design. I can load the vld designed out to 2.270 and get away with it. Sure, my mags will hold 2.295 but my bolt won't chamber. If I load 120 or 100 a max I have to drop back to 2.20-/+ .005, the 123 amax will chamber at 2.245. I know it will waste some components but I would drop back to 2.20 and work my way out to find my coal for any given bullet
 
#4
vagrendlier - COAL is all over the place. 2.295" is max mag length. I reloaded that length based on the barrel makers load. I just seated the bullet to 2.190 and it does the same thing as when I put an empty case in. The bolt closes but I can't pull the charging handle back more than 1/2". Had to pry it open again.

UA_Flyfisher - This is new Lapua brass. It may very well be an issue on my part. I've resized and trimmed to length. Like I said, I resized with a 6ppc die held .070" off the shellholder. My other options are to get a 6.5 Grendel bushing die and a smaller bushing or to get Whitley's $200 custom dies. There are a lot of people out there with 6mmAR's using the PPC dies.
 
#5
When I had first started using my 6mmAR from Whitley I had similar problems that were broken into two causes. First was from not pushing the shoulder back far enough. New brass would shoot fine and then after reloading would not chamber always, the cause was I tried to bump the shoulder back .003 and some would not go back that far or springback some so I had to move the die down to get .005 bump back average. The other problem I had was I used a Hornady 87gr bullet to mag length and the ogive was so far out it would jam the bullet and cause all kinds of problems, I had to push those bullets back to 2.175"o.a.l. to keep the bullet out of the lands. Just because your mag allows a 2.29 max doesn't mean you push the bullet all the way out there, you still have to check to make sure the bullet is short of the lands, unless you are intending to jam the bullet. You might have some measurements stacking up the wrong way and causing it not to chamber. try seating the bullet .070 deeper, .010 doesn't really make that big a difference if you are jammed by .050.
 
#6
He emailed me back within the hour. He says that I need to bump the shoulder back 1/16th turn until it chambers.

I've already seated the bullet back to 2.190"oal and bumped the shoulder of brand new brass back .007" from 1.213" to 1.206" measured with Hornady's gauges. The brass goes into the chamber far enough that sometimes the bolt doesn't catch the case.
 
#7
I don't know anything about this cartridge and my comment is only based upon what you say and the scratches on the neck of the case. It looks to me like the neck is too thick and maybe you need to turn them? You should be able to contact him and ask what the chamber was cut to. The only reason I'm saying this is I just went through this with a bolt gun in .284. If I deburred, chamferred, and FL sized the case. it would chamber, otherwise if it would chamber I had to knock it out with a cleaning rod.
 
#8
The neck may very well be too thick.

This is brand new Lapua 6.5 Grendel brass necked down to 6mm, then trimmed, chamferred and deburred. I did not neck size and haven't read anywhere that its required. The scratches on the neck are from being necked down. The scratches on the bullet are from the mag. It was loaded several times into the chamber.

The 6ppc is the 6mmAR just shorter. Same shoulder and neck. So the dies should be fine. They are commonly used for the 6mmAR. He's saying that I need to push the shoulder back 1/16th turn at a time until it chambers.

He says that if the bolt is grabbing the case, then its a problem with the case. But I've already FL resized and pushed the shoulder back so far that the empty case goes into the chamber far enough that the bolt doesn't grab it anymore.
 
#10
When I put an empty case in the chamber, half the time it goes so far into the chamber that the bolt doesn't grab it and I have to push it out with a cleaning rod. The other half, it completely chambers and the bolt closes, but I can't pull the bolt back more than 1/2"
 
#11
Oh.. And the case will come out without a cleaning rod if I hit the butt of the rifle on the ground lightly. So it's not stuck.. Just the bolt not grabbing.

Guess I'll go ahead and order the Grendel bushing die.
 
Last edited:
#12
Ok reading the above, I know on Whitley's 6mmAR you have to create a false shoulder on the initial fireforming loads because the chamber blows the shoulder a few thousandths forward. I believe the 6mm ARP chamber is similar. That would explain why the bolt can close without engaging the cartridge rim. Are there any fireforming instructions with that chamber?
 
#14
Is the follower catching the BCG (or some other mag related problem)?
It's very strange that the charging handle stops after 1/2", after all, the case has plenty of clearance in the chamber by the time it's 1/2" extracted.
Same results with or without the mag?

Joe
 
#16
UA_Flyfisher - Are you reading on the 6mmAR Turbo? There is no fire forming for the 6mmAR.

I have contacted the guy from AR15performance.com through email. He is helping me out. Or trying to anyway. He is answering my questions.

Scudzuki - It doesn't matter if the magazine is in or not, so nothings catching. I think the bolt is rotating and letting the carrier pull back 1/2" but the bolt won't pull the case out and gets stuck.

Sledge1 - I think this is a shoulder issue too. I'm curious to see what a fired case measures vs new brass.


I thought I had it fixed. I pushed the shoulder back to 1.192" and it is working properly. (New Brass Measures 1.213") I'm using Lee dies and the cases are measuring anywhere from 1.189 to 1.194" with the Hornady headspacing inserts. I can't pull charging handle out on the 1.194" and the bolt doesn't catch on the cases 1.190" and shorter. Same results from magazine or straight into chamber.


Are the rounds that the bolt isn't catching safe to fire? Or do I need to trash those. I would think it would be like fire forming. Just have to push the case out afterwards.
 
#17
Is there anyone else here shooting 6mmAR that can measure their headspacing on FL sized brass?

Is there anyone here shooting 6mmAR using 6ppc dies?


I guess I'm just going to set this brass and dies aside and order some new brass and the $200 dies from Whitley. Don't really want to mess with the Grendel bushing dies and have another issue. Thanks for everyone's responses.
 
#18
I am using neck size 6.5 Grendel die, I cannot help by directly answering your question and only offer this info for reference. I have no problems with Lapua brass. I can measure loaded and formed brass if you need me to for comparison.
 
#20
What I would do is smoke a sized case, or use machinist dykem blue on the case, carefully insert the case in the barrel and close the bolt, take it out and find where you are having fit problems by looking for places the dykem was rubbed off. I bought an AR barrel one time that the chamber was reamed off center that caused the same symptoms as your rifle....
 
#21
gree with ZX. I would make up a couple of dummy rounds, and coat them with dykem. That way, you can see where the cases are rubbing. My suspicions:
1. Shoulder needs to go further back.
2. Bullet is jammed too far into the lands.causes pressure issues too.
3. By sizing down a 6.5mm neck to 6mm, your necks may be too thick, and need to be turned. Without a bullet in the neck, the neck area could "swage" itself into the chamber. But the bullet would prevent the neck from swaging.
4. Your die is too far off the shellholder, and you may not be sizing the rest of the case as much as needed.
 
#24
So I got the Redding Type S bushing die in 6.5 Grendel with a 268 bushing. I also got new brass so I wasn't messing with anything I had already messed up. I got Hornady this time instead of Lapua. It didn't fix the problem.

The headspace measures 1.213" with the Hornady inserts. The Lapua brass with 6PPC dies were measuring the same before I pushed the shoulder back to 1.190" following his instructions to turn the die in 1/16 of a turn at a time until the problem was fixed.

I loaded a dummy round to 2.280" OAL and pushed it into the chamber by hand and let the bolt fly. Same results as before. The bolt still had 1/2" to go and it was stuck. Had to pry it open with a screw driver again.

I was sure that this was a sizing problem but now that I've got the Grendel bushing die and its doing the same thing, I'm not so sure. I've followed his instructions to a T.

I have an email out to him and am waiting for his response but was hoping y'all would have some suggestions.
 
#26
Thanks. I'm gonna wait and see what he says when he replies.

I think the scarring on the case neck happened when I necked it down from 6.5 to 6mm. I'll have to go home and look at the rest of the cases to see.

It very well may be a tight neck and I just need to turn them.
 
#27
I looked at all of the sized brass. It all has marks and scratches from being necked down. Not like the one in the picture though. That could be a from tight neck, or from being loaded from the magazine? Not sure. You can see the marks on the bullet from being loaded from the magazine.

I've emailed and called several times with no response. I haven't been able to leave a voice mail though. He may just be busy. He was answering my emails within 24 hours max.

Right now I'm stuck. The only thing I know to do is make a cast of the chamber, and I have no experience with that.
 
#29
Just some thoughts.

The case in the picture appears to not have the neck sized all the way and presumably not the shoulder bumped??? There's quite a bulge on the neck right above the shoulder and also the shoulder is rounded like it has not been touched by the die.

Have you measured the shoulder datum after sizing? Sometimes a bulge on the shoulder datum can be created if you are using a neck die. A true FL die or a form die will form the case correctly if everything is as it should be.

I would load the 105 amax to 2.265" in my 6mm ART40 and bump the shoulder .0045". First firing/sizing I'd screw the die down till there was a little resistance upon bolt closing, this created a false shoulder.

That's a good idea cutting the neck off completely and seeing if the case will chamber.

I'm thinking the chamber wasn't cut on center and/or not headspaced right.
 
#30
I've pushed the shoulder back from 1.213 to 1.190. It's not the problem. I've got new brass and new dies and same problem.

I've used the 6ppc and now Grendel bushing dies . I've pushed as far back as I can with the Grendel dies. Hornady and lapua brass. Exact same results until I get the shoulder back to 1.190" measured with the Hornady inserts. And that's probably closer to 6ppc size than 6mmAR.
 
Last edited:
#33
He's shipping the barrel and bolt back today. Here's what he said was wrong:

"This is a new one, never seen it before. When the case was in the bolt face it would push the extractor out just far enough that the back of the extractor would contact the lugs of the barrel extension.
Those extractors are thicker to make them last longer with that size rim but in this case it was too thick. I swapped out the extractor, changed the bolt to one with a little tighter headspace.
Your sized case was .006 smaller than a go gauge so now that the extractor isn’t sticking you may want to back the resize die off a little. Also this 6mmAR is a match chamber, it is designed to hold the base of the case snug to align the bullet in the bore better. It will be a little tougher to extract but when shot it should extract and eject fine. They are on the way back to you.
If you have any more trouble let me know."


I've emailed him back asking him to buy this ruined brass and primers from me and reimburse shipping since it was a problem with his product.
 
#35
Well at least the problems figured out and you can go on with life. I hate it when things like this happen to me! They happen more often than I care to acknowledge.

Expand those necks back up to 6.5, then down and create the false shoulder again or seat the bullets out far enough to hold the case against the bolt. Might have to single feed if seating the bullets out. Those marks on the necks will straiten out once they've smacked against chamber a few times.
 
#36
Finally got out to shoot it. This was my first 5 shots. (It rained on the target overnight.)
CAM00015_zps4aa96a17.jpg


And then straight to 492 yards after zeroing. I think I was 7 for 10 just holding for wind.

[video]http://s1232.photobucket.com/user/corylee4870/media/CAM00012_zps47afba7a.mp4.html[/video]


95 smk seated at ~2.290"
28gr H4895
2800 FPS
SD of 9
That's about 33.7moa to 1000 out of an Ar15 and still supersonic. I'm still hoping to get close to 2900fps.
 
Last edited:
You must log in or register to reply here.

Similar threads

RTTY
Chambering issue after expander mandrell.
Replies
48
Views
885
Ex E6
Ex E6
sacklunch
Pressure question…virgin vs fire formed
Replies
12
Views
418
912173
912173
Mumzergadol
7PRC problem. Brand new prefit barrel, reputable smith, bolt wont close on freshly sized new brass
Replies
10
Views
398
Mumzergadol
Mumzergadol
L
30-06 COAL and CBTO with 178 ELDX
Replies
12
Views
257
LambChoppa
L
Y
How smoothly should my resized cases load into the chamber with bolt ejector removed?
Replies
24
Views
471
918v
918v
Top Bottom
Back
Home
Forums
Merch
Alerts