View Full Version : CMMG 10.3" barrel - questionable?
I just disassembled my CMMG 10.3" upper to install a Larue handguard. First of the all the taper pins were SOFT. The pics show some of the mushrooming but most is gone because I managed to force them through. Also the rear taper pin hole drilled into the bottom of the barrel doesn't make me happy. Now I haven't removed a lot of gas blocks but the rear hole is almost drilled so low that the bottom of the barrel is gone.
Thoughts?
I'm thinking of putting it back together-selling it cheap and getting an LMT upper or a Sabre Defence barrel.
(As an aside, being a mechanical engineer I'm absolutely thrilled to have found an AR15 site with people that think and aren't blinded by gun jewelry.)
http://audiemurphy.net/bbl-bottom.jpg
http://audiemurphy.net/bbl-side.jpg
http://audiemurphy.net/pins.jpg
Dont sell it and take a loss on it sent it back to CMMG and have them either make it right or get refund.
Well I just sent them an email with pics and respectfully asked how they intended to remedy the situation. Although I cannot say I would really want a CMMG barrel in what is going to be my go to weapon. This isn't the only issue I've had-I also had a bolt with a bad ejector from them. I'm disappointed having spent more money for their product expecting to get something better than a DPMS/RRA/Bushy upper.
Hopefully they'll take care of it and I can post a happy ending.
Here's a question: On the CMMG upper I have with M4 ramps: will an LMT or Sabre barrel extension line up with these? I'm hoping it's cut to spec.
Give them a chance to get it right.
Some forum members seem to be down on CMMG, but I've had good luck with them.
Please let us know how it turns out.
I've had no troubles with my 10.3, but I would contact them about the issue rather than posting on the boards to give them a chance to stand behind their product.
I've had no troubles with my 10.3, but I would contact them about the issue rather than posting on the boards to give them a chance to stand behind their product.
Well I was more or less asking if the taper pin holes were worth harassing them about.
It doesn't appear that it'll affect the funtion of the rifle. But if it perturbs you a tx to them won't hurt. Make them work for your money until you get what you want.
I've seen the same on some old Colt..
Get a refund from CMMG and buy a quailty LMT SBR 10.5'' .
yup thats what I would do. I was going to order a 18" SPR stainless barreled upper from them this week until I saw those pics with a MUR upper and other doodads. I have heard too many bad stories lately about their work going downhill.
? On A couple of Colt lightweight barrels I have, there is no "bottom" to the taper pin holes.
Heavy Metal
09-17-07, 08:31
Lightweights are thinner at this point.
I have 2x 10.3 CMMG's, a Colt 10.3 and 2 x 10.5 LMT's.
All are virtually indistiguishable - I've pulled the front sights off both the CMMG's and not had any issues.
Secondly on several Colt M4 and M4A1 (RO921HB) barrels I have - the front sight gas block has been drilled near the bottom and it is open at that point. No worries.
The Archangel
09-17-07, 16:49
If you do decide to get rid of the CMMG barrel, I'll take it. We can work the details out in PM.
AR15barrels
09-17-07, 17:43
Ideally, the taper pins should only cut half-way into the barrel.
The hole should not be so far up into the barrel that there is a complete circle all within the barrel.
Your complaining about the pin hole being close to the edge of the barrel for the wrong reason.
The complain SHOULD be that there actually IS a hole in the barrel instead of just a crescent cut.
Ideally, the taper pins should only cut half-way into the barrel.
The hole should not be so far up into the barrel that there is a complete circle all within the barrel.
Your complaining about the pin hole being close to the edge of the barrel for the wrong reason.
The complain SHOULD be that there actually IS a hole in the barrel instead of just a crescent cut.
Thanks Randall. As I haven't seen hardly any stripped barrels in person (drilled for taper pins) I wanted some feedback. I do see your point about the higher hole being a concern. I suppose if it were too close to the bore the metal would be thin resulting in a hot spot around the cut. Anyways it shoots well, so I'm going to put it back on with the new Larue handguard. However, I'll be buying some new taper pins that aren't soft. Trust me on the pins they were terrible before they got through. The first and second strikes were square and they mushroomed almost completely flat. I almost doubt they were ever hardened.
Granted, I only own .625" barrels now, but all of my taper pins have only been halfway into the barrel when I removed the FSB.
AR15barrels
09-17-07, 19:14
Granted, I only own .625" barrels now, but all of my taper pins have only been halfway into the barrel when I removed the FSB.
Good:
http://ar15barrels.com/tech/colt-fsb-park.jpg
Colt's pin cuts form a perfect half-circle cut into the barrel.
Bad:
http://ar15barrels.com/tech/lmt-fsb-park.jpg
Note how the LMT barrel has the holes all the way up into the barrel, creating a full circle.
Randall is that the standard way LMT does it?
AR15barrels
09-18-07, 00:21
Randall is that the standard way LMT does it?
Yes.
Just one more place where colt does it a little bit better.
To be fair though, I did show 0.625" colt barrels.
Colt's 0.750" barrels are not perfect crescents.
They are more like 3/4 of a pin in the barrel, leaving an open slot.
I don't have a picture handy to show exactly what I mean, but you get the idea...
Not the best pic (I thought I had a better one hosted but it appears not)
http://img.photobucket.com/albums/v193/EvilKev/Weapons/M4build005.jpg
Colt M4A1 - about a 75% (of the pin) depth crescent.
next time I rip one of our guns apart here - I will take some better ones
Robb Jensen
09-18-07, 05:21
I just disassembled my CMMG 10.3" upper to install a Larue handguard. First of the all the taper pins were SOFT. The pics show some of the mushrooming but most is gone because I managed to force them through. Also the rear taper pin hole drilled into the bottom of the barrel doesn't make me happy. Now I haven't removed a lot of gas blocks but the rear hole is almost drilled so low that the bottom of the barrel is gone.
Thoughts?
I'm thinking of putting it back together-selling it cheap and getting an LMT upper or a Sabre Defence barrel.
(As an aside, being a mechanical engineer I'm absolutely thrilled to have found an AR15 site with people that think and aren't blinded by gun jewelry.)
http://audiemurphy.net/bbl-bottom.jpg
http://audiemurphy.net/bbl-side.jpg
http://audiemurphy.net/pins.jpg
I've used CMMG barrels for builds of my own and for customers. The taper pins are always soft, I replace them with Colt or DPMS taper pins. After the pin upgrade everything else works just fine. I wouldn't lose any sleep over where the taper pin hole is in the barrel as long as it's not through the bore.
Yes.
Just one more place where colt does it a little bit better.
To be fair though, I did show 0.625" colt barrels.
Colt's 0.750" barrels are not perfect crescents.
They are more like 3/4 of a pin in the barrel, leaving an open slot.
I don't have a picture handy to show exactly what I mean, but you get the idea...
So is this a result of workmanship?
Or is it a result of the way the FSB that each manufacturer uses lines the holes up?
Aside from being "different than colt", what's the functional reason for the shallower cuts? Is it a heat issue? Harmonics? Cosmetic?
Just one more place where colt does it a little bit better.
If you get unparked surfaces under the FSB in your shop do you park them? Or CAN it be done? Is it worth the hastle?
AR15barrels
09-20-07, 19:40
So is this a result of workmanship?
Or is it a result of the way the FSB that each manufacturer uses lines the holes up?
Aside from being "different than colt", what's the functional reason for the shallower cuts? Is it a heat issue? Harmonics? Cosmetic?
Every manufacturer is using almost the same FSB forgings.
How deep the pin is set into the barrel is mostly a function of how each company made their drilling fixture.
Some choose to put the pin in the middle of the pad on the FSB forging.
This works great on 0.625" barrels, but leaves the pin WAY too high on 0.750" barrels.
Colt pulls the pin down as far as they can to ensure that the whole pin is not going through the barrel.
The latter is desireable as it helps create a better seal at the FSB-gas port junction.
The pin being partly in the barrel and partly in the FSB makes the taper pull the FSB forging DOWN as you set the pin into place.
The closer you get to a 1/2 crescent cut, the more of this benefit you get.
AR15barrels
09-20-07, 19:42
If you get unparked surfaces under the FSB in your shop do you park them? Or CAN it be done? Is it worth the hastle?
The whole barrel has to be blasted in order to re-parkerize it.
It's not worth the hassle in my opinion, but some people have me do it.
It's usually done when the barrel is getting re-profiled as well.
Every manufacturer is using almost the same FSB forgings.
How deep the pin is set into the barrel is mostly a function of how each company made their drilling fixture.
Some choose to put the pin in the middle of the pad on the FSB forging.
This works great on 0.625" barrels, but leaves the pin WAY too high on 0.750" barrels.
Colt pulls the pin down as far as they can to ensure that the whole pin is not going through the barrel.
The latter is desireable as it helps create a better seal at the FSB-gas port junction.
The pin being partly in the barrel and partly in the FSB makes the taper pull the FSB forging DOWN as you set the pin into place.
The closer you get to a 1/2 crescent cut, the more of this benefit you get.
Awesome explanation, thank you! I guess it didn't occur to me that the holes in the FSB for the taper pins were drilled with the fsb in place. I assumed that they would have existing holes, and that the holes would be standard. You learn something every day.
Awesome explanation, thank you! I guess it didn't occur to me that the holes in the FSB for the taper pins were drilled with the fsb in place. I assumed that they would have existing holes, and that the holes would be standard. You learn something every day.
Yep. Years ago you'd get people wanting to swap their FSB out with an F marked version to go with the flat top they just bought from some bottom feeder.... as though you could simplely swap the parts....
No Senor!
AR15barrels
09-21-07, 14:54
I guess it didn't occur to me that the holes in the FSB for the taper pins were drilled with the fsb in place.
Here is LWRC's FSB drilling fixture:
http://ar15barrels.com/tech/fsb-installation.jpg
I'm actually working on a new drilling fixture of my own this week.
The two main complaints I have with CMMG barrels are the butter soft taper pins and the razor sharp barrel extensions that cut chambering bullets.
Other than that they are fine. :rolleyes:
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