GM-M29 barrel

[1168]

Good afternoon,

I was wondering if anyone here has messed with the following barrel: https://www.gmriflebarrel.com/gm-m29...ato-1-7-twist/ and has anything to say about it. Particularly in comparison to .gov contract guns.

From the website: “5.56 mm, 1:7 twist, 14.5" long, 41V50 steel, weighs 1.7 lbs., carbine length, extension with M4 feed ramps, chrome line bore and chamber, phosphate finish, button rifled, air gauged, stress relieved. Barrel is not pinned for the front sight base.”

It looks to have a profile similar to the Criterion Hybrid, conceptually. Kinda like Gov’t, but better, and not a “long straight taper”, pencil, or “SOCOM” type profile. Looks like it should balance well. There are some interesting claims in the reviews.

Said barrel would be going inside a 13” URX4 or G Mk8 on a beater gun, and I am also considering a variety of other 14.5/.7” barrels, such as Colt 6920/Gov’t, MMC, Colt, or Rem “SOCOM”, BA 14.7” Pencil, Ba Hanson, Spikes CHF, BRT CHF, and GM-M19, some of which I already have. I also have a buddy looking to assemble a very similar upper with a 13” G Mk8 or a similar quad, and has not yet picked a barrel, so discussion in comparison to other barrels is welcome, but I’d like it to be mostly about this barrel, or at least this brand.

[1168]

E9EEF96A-63DA-4EEF-B7DB-4B2E7CBEB94A.png

[Leonidas24]

I think 26th INF has some experience with these, or Green Mountain at least. Hopefully he'll chime in.

The little I've seen is that they are a bit wide on gas port diameter.

[vicious_cb]

I think 26th INF has some experience with these, or Green Mountain at least. Hopefully he'll chime in.

The little I've seen is that they are a bit wide on gas port diameter.

Pretty much this, other than the larger gas ports (0.071") they are good barrels.

In regard to your usage, if you are putting it under a longer handguard you might as well go midlength gas. The real niche I think GM fills is that they are the only decent barrel maker producing CARBINE length barrels in not stupid profiles ie. gov't profile and their price point.

[everready73]

I had 2 gm m8 barrels which is a 16"middy. Both performed well and were good quality. I sold both the uppers I had with these but they were a little over gassed from what I remember. Accuracy was good for the type of barrel it is, about 1.5 moa

I switched to using Sionics as they are ported better and have some extra qa/qc steps for not much more money, those have been vapor ware for the last year though

[1168]

Thanks for the replies so far. I see that overgassed is a common theme. I tend to use an EZ Tune tube with most everything at this point, so its not as big of a deal as it could be. Except in principle, of course.

I think 26th INF has some experience with these, or Green Mountain at least. Hopefully he'll chime in.

The little I've seen is that they are a bit wide on gas port diameter.

I tried to PM him, but I have not seen him on here lately, and cannot find him in the User Directory.

Pretty much this, other than the larger gas ports (0.071") they are good barrels.

In regard to your usage, if you are putting it under a longer handguard you might as well go midlength gas. The real niche I think GM fills is that they are the only decent barrel maker producing CARBINE length barrels in not stupid profiles ie. gov't profile and their price point.

What barrel did you measure .071”? Was that another carbine gassed 14.5”? I don’t mind carbine gas, generally.

I had 2 gm m8 barrels which is a 16"middy. Both performed well and were good quality. I sold both the uppers I had with these but they were a little over gassed from what I remember. Accuracy was good for the type of barrel it is, about 1.5 moa

I switched to using Sionics as they are ported better and have some extra qa/qc steps for not much more money, those have been vapor ware for the last year though

Could you elaborate on your accuracy testing? Did Sionics even do a 14.5”?

I actually have a SPR type barrel from GM that I should shoot someday.

[everready73]

I usually just use 16"barrels to avoid p/w if not going sbr or pistol. I was referring to Sionics 16"

I test accuracy using 5 shot groups at 100 yards. I use 77 grain imo razor core and australian outback 69 grain for accuracy tests usually. I can't remember which one shot better and don't have log book handy

[vicious_cb]

What barrel did you measure .071”? Was that another carbine gassed 14.5”? I don’t mind carbine gas, generally.

0.071" is their porting for 14.5 and 16 carbine length barrels.

[1168]

0.071" is their porting for 14.5 and 16 carbine length barrels.

A bit big. Not quite a dealbreaker, since its so easy to choke them down these days, although I wish Colt port sizes were copied more frequently.

[DG23]

SNIP...

Could you elaborate on your accuracy testing?

SNIP...

I actually have a SPR type barrel from GM that I should shoot someday.

You should. They make good barrels. Well worth your time to try out what you have at least and form your own opinion.

These are all Colt carbine uppers / barrel assemblies as they came from complete factory carbines with nothing added, swapped out, or exchanged for a different part. Only removed the hand guards for the picture...



The one in the middle has a Green Mountain barrel with same profile as what you are looking at.

A green Mountain barrel that Colt decided to source / contract and use on some of their carbines that they were selling to the general public...