Will 308AR w/ rifle length gas & SOPMOD work?

[68bthp]

I want to have Krieger cut their 20" M110 308 service barrel down to 18", but they're telling me that they won't be held responsible if there's any functioning issues.

This gets me nervous, and makes me wonder if I can expect the barrel to work reliably with an LMT SOPMOD collapsible stock. I've also noticed that Fulton Armory sells 16" and 18.5" barrels in rifle length gas systems.....but don't offer any of their rifles with a collapsible stock.

I'm not familiar with the functioning differences of buffers and springs between a fixed stock and collapsible stock, and wonder if I'm going to have reliability probs.

 

[ORD]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

It SHOULD work, but will require some different parts and MAY require opening the gas port in the barrel a little bit.

If you have a fixed/rifle stock on the rifle now, you will need a different buffer tube, buffer and spring. To add any AR-15 collapsible buttstock to a 308 AR, you will need a specially designed/built 308 Carbine buffer from Slash, as well as a modified buffer spring. See here for more details: http://www.heavybuffers.com/ar10carbine.html

Now, with the proper buffer/spring combo, an 18" barrel with a rifle length gas system should function fine. However, as with any rifle, your mileage may vary. If you get some function issues, you may have to open up the gas port a little bit and several people here have done similar jobs on their rifles along those lines so help isn't far away if you need to go that far.

 

[BCP]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

Just to be clear you already have it on a rifle and want it cut down? If so it should run just fine at 18" however you may have to experiment with different buffers and springs to get it running 100%.

If you want an M110 except 18" then just buy an 18" barrel to begin with...

edit: FWIW I have a 16" with a rifle gas system and a magpul acs stock and it runs great so as long as you have the right gas port + buffer and spring combo it will definitely work.

 

[pupdawg]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

I run a rifle gas system on my factory LW AR10T barrel cut down to 18". Runs fine never had a stoppage yet for well over 2000 rounds on the cut barrel so far. I assume that if the gas port dimensions are the same as Armalite's AR10T then the Kreiger will run fine also.

I also run Slash's CAR-10 buffer like ORD said above with a magpul UBR. Contact Slash (Clint) and he can recommend the proper buffer for your configuration.

Hope this helps.

 

[68bthp]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BCP</div><div class="ubbcode-body">Just to be clear you already have it on a rifle and want it cut down? If so it should run just fine at 18" however you may have to experiment with different buffers and springs to get it running 100%.

If you want an M110 except 18" then just buy an 18" barrel to begin with...

edit: FWIW I have a 16" with a rifle gas system and a magpul acs stock and it runs great so as long as you have the right gas port + buffer and spring combo it will definitely work. </div></div>

Thanks, to all you gentlemen for the helpful input.

Actually, I had already tried an 18.5" 308 Fulton barrel built onto a SOPMOD with slash's buffer and spring. But, I was seeking tighter clustering then the 1 1/4" groups and pulled the rifle apart. During the short time that I fired it, it seemed to work well, and I took the reliable functioning for granted. But.... I was more focused on developing accuracy loads and never really paid much attention about reliability. Therefore, Krieger's statement made me take a step back and wonder if I was lucky with the few rounds that I fired.

I have checked the archives here (April 28) to see that other members such as "9H" and "Hamilton" also report good performance cutting back barrels, but suggested that the gas port is a .1" opening. When I get my Fulton barrel back from the a barrel company that held it for 8 months and did nothing,(if I really ever get it back from them....long story)I'll measure the port.

Thanks again. I feel better about this now, and I really had to be sure what I was doing before I went against the policy of a great company like krieger.

 

[9H_Cracka]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

I cut the same barrel to 18". Unsuppressed with the PRI adjustable gas block wide open it is slightly undergassed but functioning fine with stout match ammo using the Magpul UBR stock with a 308 buffer and spring in it.

Cutting the barrel in front of the gas port reduced the dwell time, therefore reduces the amount of gas going into the gas tube.

If you find it does not function in your application, 2 competent AR smiths told me they build their rifle length/18" guns with the gas hole in the barrel drilled at .100" which is slightly bigger than when doing a 20" rifle length, so worst case scenario is you need to open the gas port up a bit in your barrel.

 

[BCP]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 68bthp</div><div class="ubbcode-body">1 1/4" groups</div></div>

That's how my fulton barrel shoots with pulled 175smks; with 168 FGMM it is tighter.

WTF problem did you have with the barrel that took it out of your hands for 8 months??? I had a problem with my Fulton in that it was short chambered but they fixed it in a couple weeks...

 

[68bthp]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: _9H</div><div class="ubbcode-body">I cut the same barrel to 18". Unsuppressed with the PRI adjustable gas block wide open it is slightly undergassed but functioning fine with stout match ammo using the Magpul UBR stock with a 308 buffer and spring in it.

Cutting the barrel in front of the gas port reduced the dwell time, therefore reduces the amount of gas going into the gas tube.

If you find it does not function in your application, 2 competent AR smiths told me they build their rifle length/18" guns with the gas hole in the barrel drilled at .100" which is slightly bigger than when doing a 20" rifle length, so worst case scenario is you need to open the gas port up a bit in your barrel.
</div></div>

When you say you "cut the same barrel to 18" are you referring to the Krieger 20" M110 barrel, or the Fulton 18.5" barrel?

I already have a Daniel Defense FF rifle length rail I intend to put back on this project. I will be buying an Armalite .875 compression gas block which is not adjustable. Therefore it is important for me to know what works best and know what size gas port to have krieger put in the new barrel. I might as well get it done right from the start when I place my barrel order with Krieger. I'm already going against their standard 20" barrel specs (and warranty), and so I don't think they will provide much helpful input about the gas port size. At this point, they'll just be polite and tell me "Whatever you tell us to do, we'll do it for you, but we're not going to warrant it" That's reasonable and OK....as long as I know what to instruct them.

 

[68bthp]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BCP</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 68bthp</div><div class="ubbcode-body">1 1/4" groups</div></div>

That's how my fulton barrel shoots with pulled 175smks; with 168 FGMM it is tighter.

WTF problem did you have with the barrel that took it out of your hands for 8 months??? I had a problem with my Fulton in that it was short chambered but they fixed it in a couple weeks... </div></div>


I'm a fussy handloader and demand accuracy or I'm not happy with the rifle, and I'll dump it. I tried MANY different loads with this 18.5" barrel. The Hornady 168 BTHP's with 41.3 of H4895 was the best. For accuracy tests, I go so far as weighing bullets, double weighing powder charges, checking cartridge concentricity, and benching the rifle while watching wind flags. My scope is set at 24X. Under these conditions, I've had many groups with 3 shots in 1/2" or 4 shots in 5/8". But, most groups average 1 1/4" when taking the one or two flyer shots into the group. I have targets with all 5 shots in 5/8" or 3/4", but I can't ever repeat it in the next attempt or two. The 18'5" Fulton barrel is honestly an easy 1 1/4" grouper, with 4 shots often in 1". To Fulton's credit, this is DARN GOOD barrel considering it is chrome lined and only about 2 1/2lbs. But, you are reading the anal input of a guy who's normal 5 shot groups are 1/2" or better with his two varmint rifles. My mistake was thinking that I could get consistant 3/4" groups or better out of a light chrome lined barrel because of Fulton's rave reviews, and the fact that the 18.5" barrel is a Krieger Criterion. At the time when I purchased the Fulton barrel, they did not have the 1 1/4" accuracy stats posted on their websight, and I believed their "no accuracy loss with our chrome lining process". Well, it is very accurate for what it is, but it's not the 5/8" 5 shot groups I'd like.

<span style="font-weight: bold">As for your wondering why or who it was that had my barrel tied up for 8 months?</span> I'm new at this websight, and don't yet know how tolerant the staff would be if I mentioned the name of the barrel manufacturer that did that to me. It was <span style="text-decoration: underline">not</span> Fulton. It's a fairly well known name in the business, and always has the one guy (the owner) who answers the phone. The man is a calm and patient sweet talking liar who falsely inspires confidence. I sent the barrel to him so the contour could be duplicated without chrome lining and be made just a little bit heavier. It remains to be seen if I will actually ever get my Fulton barrel back from him in the coming few days. It was sent to him in perfect condition with only 200 rounds through it before Thanksgiving last year. He's done nothing with it, except to tell me (only after I inquired 6 1/2 months later)that UPS lost it. Well, now 8 months later UPS managed to find it. Now he wants a payment up front before he starts the new barrel. (yea...right!) I wonder what shape my Fulton barrel will be in after being "lost". I'm worried it was thrown around the shop cement floors,and rusted, dinged, or Lord Knows what....<span style="font-style: italic">IF</span>, I actually get it back.

 

[9H_Cracka]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

I am referring to the Krieger M110 barrel.

 

[BCP]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

1) AR308's are difficult to shoot

2) AR308's like to throw the last round in the mag differently

So if you're getting tight groups with one flier, wider groups with a flier I'd think it was those two factors and not the barrel.

Once you (hopefully) get your barrel back if you still aren't happy with it consider either a drop-in match barrel ala rainier ultra match etc or selling everything and having a rifle built by a builder like GAP.

 

[Jgun]

Re: Will 308AR w/ rifle length gas & SOPMOD work?

I have a .308 AR that I put together myself. When I contacted Krieger about a barrel they told me the same thing. I ended up going with an 18" ABS carbon wrapped Mike Rock barrel with rifle length gas system. When I spoke to Mike to order the blank, he assured me that I should have no trouble with it. So far that has been the case. I have a CTR stock on it with an AR 15 buffer tube and the HB.com extra heavy buffer and spring.