Green Mountain 1/8 twist M16A1 barrel - any one have one ?

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[ARCHIVED THREAD] - Green Mountain 1/8 twist M16A1 barrel - any one have one ?

Posted: 12/9/2010 6:10:06 AM EDT

From the Green Mountain website:

"M16 A1 5.56mm 20" Barrel, 1:8 twist, 41V50 Mil spec vanadium steel, fully machined and assembled with extension, chrome lined bore and chamber, drilled gas port, parkerized finish.Original 1960s era M16 A1 spec. Click "view detail print" for more information... "

http://www.gmriflebarrel.com/productdetail.aspx?id=GM-M16

Any one have one ? The description is for M16A1, but the photo on the site looks like Government Profile (light under handguard, heavy at FSB). I am sending an e-mail to verify. I am thinking about one of these for my 2nd 605 build - 1/8 twist should cover 55 to 62 grain projectiles, chrome lined, new manufacture, dont have to cut up an old barrel - seems good to me.

ETA : they are listed at $149 on the website.

Posted: 12/9/2010 7:21:00 AM EDT

[#1]

this is the barrel you want for a 605 conversion

I bought a couple of these for just that purpose, but haven't had a chance (or the money) to do anything with them yet...but I'm hoping to send at least one of them out to Heatnbeat soon

Posted: 12/9/2010 8:07:21 AM EDT

[#2]

Their link for the "M16 A1 5.56mm 20" Barrel, 1:8 twist" Detail Print, results in a Not Found message.

This is the correct link here.

It would be great if they added the diameter specs to it, like they have on their other prints.

Edit: crackedcornish, can you relate the dia specs for your 1-12 barrels? Thanks.

Posted: 12/9/2010 8:54:07 AM EDT

[#3]

chris, unfortunately I don't have the means to accurately measure the diameter of the barrel, but I can tell you that my .625" fsb slides up to the step for the gas hole and is just a bit too snug to slide up onto it, so it should be a nice tight fit when the sight actually goes into position for mounting

You could probably get that info directly from Green Mountain, they're very easy to work with

Posted: 12/9/2010 9:50:48 AM EDT

[#4]

looks like a M16A2 govt heavy foward bbl in the pic....

Posted: 12/9/2010 1:52:38 PM EDT

[#5]

Quoted:
this is the barrel you want for a 605 conversion

I bought a couple of these for just that purpose, but haven't had a chance (or the money) to do anything with them yet...but I'm hoping to send at least one of them out to Heatnbeat soon

I already have a 1/12 605 barrel (old barrel that had a screwed up muzzle, so cutting it off actually made it usable again) I want to be able to use heavier projectiles and not just the 55 grain stuff.

The "short" 1/12 barrels are a good bargain for 605 builds.

Posted: 12/9/2010 2:10:58 PM EDT

[#6]

Quoted:

Quoted:
this is the barrel you want for a 605 conversion

I bought a couple of these for just that purpose, but haven't had a chance (or the money) to do anything with them yet...but I'm hoping to send at least one of them out to Heatnbeat soon

I already have a 1/12 605 barrel (old barrel that had a screwed up muzzle, so cutting it off actually made it usable again) I want to be able to use heavier projectiles and not just the 55 grain stuff.

The "short" 1/12 barrels are a good bargain for 605 builds.

have you tried shooting some of the slightly heavier loads through your 1/12?.....I have a couple that shoot anything up to and including Speer's fmj/bt 62's superbly.

Posted: 12/10/2010 3:12:32 AM EDT

[#7]

Quoted:
- 1/8 twist should cover 55 to 62 grain projectiles.

1/8 should cover 77's at mag length and even 80's single loaded. If you're not shooting high power "across the course" 80's aren't practical but then you won't be shooting an A1 XTC anyway. 77's rock out thru 600.

Posted: 12/10/2010 5:45:43 AM EDT

[#8]

Quoted:
...
have you tried shooting some of the slightly heavier loads through your 1/12?.....I have a couple that shoot anything up to and including Speer's fmj/bt 62's superbly.

I tried some and my group opened up from 2" with 55 grn to 12" with 62 grn - the barrel I have does not like heavier bullets (iron sights/ 100 yards)

Posted: 12/10/2010 5:52:35 AM EDT

[#9]

My 1/12 twist barrel handles 62grain ammo OK...In hot weather. (Ie: 95+ degrees, humid, texas, 100 yards off a bench) Couldn't tell a difference...

1/8 is weird, wonder why not 1/9, but I'm sure they shoot just fine. They have a good reputation, since they made the barrels in the colt kits going around now.

Posted: 12/10/2010 8:27:59 AM EDT

[#10]

Quoted:
My 1/12 twist barrel handles 62grain ammo OK...In hot weather. (Ie: 95+ degrees, humid, texas, 100 yards off a bench) Couldn't tell a difference...

1/8 is weird, wonder why not 1/9, but I'm sure they shoot just fine. They have a good reputation, since they made the barrels in the colt kits going around now.

They made some of them.Not all.I think the green mountain rep said they made them for century or one of the other vendors when the kits first came out.I'm still guessing that Citadel made most of the others.

Posted: 12/10/2010 8:52:37 AM EDT

[#11]

Quoted:
They made some of them.Not all.I think the green mountain rep said they made them for century or one of the other vendors when the kits first came out.I'm still guessing that Citadel made most of the others.

Crap, he's right. They do have a good reputation, but they did NOT make all of the barrels.

Posted: 12/10/2010 10:36:24 AM EDT

[#12]

Quoted:

Quoted:
...
have you tried shooting some of the slightly heavier loads through your 1/12?.....I have a couple that shoot anything up to and including Speer's fmj/bt 62's superbly.

I tried some and my group opened up from 2" with 55 grn to 12" with 62 grn - the barrel I have does not like heavier bullets (iron sights/ 100 yards)

Try some 62's from a different manufacturer. I'm just sayin'. They're not all created equal and they don't all perform equal in different rifles.

Posted: 12/10/2010 11:22:00 AM EDT

[#13]

Quoted:

Quoted:
...
have you tried shooting some of the slightly heavier loads through your 1/12?.....I have a couple that shoot anything up to and including Speer's fmj/bt 62's superbly.

I tried some and my group opened up from 2" with 55 grn to 12" with 62 grn - the barrel I have does not like heavier bullets (iron sights/ 100 yards)

It is not about bullet weight, but length and bearing surface.

The M-855 bullet is 0.905" long +/-. You will need a 1/9" twist, or faster, to stabilize this bullet. Yes, in some conditions, and at high velocities, you could stabilize this bullets with a 1/10" twist, but 1/9" is the minimum.

There are some shorter 60gr Flat Base bullets that could do better, but with a 1/12" twist, just stick with the 50gr to 55gr bullets.

Posted: 12/10/2010 11:31:56 AM EDT

[#14]

I shot some LC and Port 62s and they key holed with my 1/12.

Posted: 12/10/2010 5:39:58 PM EDT

[#15]

I just shoot Ball M193 out of them all.No worries.

Posted: 12/11/2010 7:20:03 AM EDT

[#16]

Quoted:

I shot some LC and Port 62s and they key holed with my 1/12.

This is what happens 90% of the time in a 1/12 barrel despite what some will tell you with M855. Those who often tell you about stabilizing 62 grain bullets with kick arse results are shooting shorter FMJ lead core bullets and not the M855. As stated earlier by another poster it is bullet length not weight that causes the problem, the M855 long for it's weight. 1/7 is the best twist for the widest range of projectiles although 1/8 is acceptable also.

Posted: 12/11/2010 9:38:26 AM EDT

[#17]

Quoted:

Quoted:
Those who often tell you about stabilizing 62 grain bullets with kick arse results are shooting shorter FMJ lead core bullets and not the M855. As stated earlier by another poster it is bullet length not weight that causes the problem, the M855 long for it's weight. 1/7 is the best twist for the widest range of projectiles although 1/8 is acceptable also.

Again, I was shooting M855 (Steel core, magnetic) rounds out of a 1/12 barrel, and they worked just fine at 100 yards, but again, it was a very hot (95+) day, and I understand that as temperatures drop rounds don't stabilize as well. The groups I were getting were larger than what I'd have expected with 55grain rounds, but I didn't have any keyholing or huge shotgun like patterns. The only reason I was shooting the 62 grain ammo through that rifle was that I'd screwed up when I left home (Indiana) and was all the way in Houston, TX, before I realized I'd grabbed the wrong boxes.

For what it's worth, about five days later I had the same rifle out in ~50 degree weather back closer to home, and the same 62 grain ammunition was flying all over the place at distances of 50-75 yards, so again, I would never intentionally repeat that experiment since I bet it's mostly pointless to try it most times and probably just a waste of ammo. My buddies took me to the local shop, I picked up some M193, and the rifle was shooting AOK again.

As for the best twist, I'm going to say that 1/9 is probably my favorite, since it seems to handle just about everything, and doesn't wear out as fast as 1/7. But hey, the great thing about America is that we can still spend our own money of what we want...So far...

Posted: 12/11/2010 10:27:15 AM EDT

[#18]

yeah, a 1/12 that will shoot heavier stuff is definitely an exception to the rule, but if you shoot the stubbier fmj bt's you're more likely to run across one

Posted: 12/11/2010 2:18:28 PM EDT

[#19]

1-9 twist is the most popular produced AR barrel today for a reason. It's the most ammo friendly. Buy one of each twist if you got the coins. I want one of those 1-12 $90 Green Mountain barrels so bad I can taste it. Food or a new barrel, decisions, decisions.

Posted: 12/15/2010 7:25:40 PM EDT

[#20]

I confirmed today during a conversation with the rep at Green Mountain that the 1:8 AR barrel is Government profile (skinny under the handguards, .750" at the gas block, and heavy out to the muzzle).

Harlan
NoDak Spud LLC