AR-15 Barrels

[Dietz]

pretty much no one besides fn and colt use to spec gas ports anymore even dds gas ports aren't to spec there is too much issue with under powered ammo like wolf, tula, herters etc with to spec gas ports. That being said just because the gas port isn't to spec doesn't mean the barrels are bad dd and bcm have out of spec gas ports for 10.5" and run just as good as colt and fn.

But good brands in my experience of 20k+ rounds through ar pattern rifles annually is that kac, dd, colt, fn, chf noveskes and bcm are going to be the best for a reliable and 2 moa or better barrel.

To-spec doesn't mean ####.

LMT makes the only proper 10.5 barrel on the market with a Crane-spec .071 gas port (the only port size a 10.5 should have, other than on a dedicated suppressed barrel). Colt's are WAY overgassed at .093 (they use their own spec, not an issue since they are unobtanium), as well as DD at .082 and everybody else, FN I don't know but good luck finding one. BCM doesn't make a 10.5.







OP, this thread is worthless without some numbers.

What was the actual gas port diameter on the Rainier barrel? What ammo were you running? And what did you get it opened to?

 

[katazone]

To-spec doesn't mean ####.

LMT makes the only proper 10.5 barrel on the market with a Crane-spec .071 gas port (the only port size a 10.5 should have, other than on a dedicated suppressed barrel). Colt's are WAY overgassed at .093 (they use their own spec, not an issue since they are unobtanium), as well as DD at .082 and everybody else, FN I don't know but good luck finding one. BCM doesn't make a 10.5.







OP, this thread is worthless without some numbers.

What was the actual gas port diameter on the Rainier barrel? What ammo were you running? And what did you get it opened to?

It was .071. And it spit out MFS, barnhaul shells right next to me and had FTF often. Norinco higher powered cycled but still didn't push the Bolt back enough from an observation from the guy next to me. I am more conserened anout the bulk ammo as I purchase a lot of those.
Casey , my gunsmith opened it up to .083 I believe the first time, still FTF.
I have no idea how big he went the second time but my guess is probably like the Colt at around .093 and problem fixed.
Shot everything from Stainless MFS to American Eagle without any issue.
I know LMT is fantastic. Now it is very possible that there is no set standards when it comes to custom builds. Buffer, spring all interact. I don't know.....your guess is as good as mine.

 

[Dietz]

It was .071. And it spit out MFS, barnhaul shells right next to me and had FTF often. Norinco higher powered cycled but still didn't push the Bolt back enough from an observation from the guy next to me. I am more conserened anout the bulk ammo as I purchase a lot of those.
Casey , my gunsmith opened it up to .083 I believe the first time, still FTF.
I have no idea how big he went the second time but my guess is probably like the Colt at around .093 and problem fixed.
Shot everything from Stainless MFS to American Eagle without any issue.
I know LMT is fantastic. Now it is very possible that there is no set standards when it comes to custom builds. Buffer, spring all interact. I don't know.....your guess is as good as mine.

I've shot thousands and thousands of MFS and Branaul crap through my 10.5 LMT and still do (that's basically all I shoot after I went through my crates of yellow box and white box Norinco and AE223), plenty strong ejection 10-12 feet away at my 4 oclock and that's with an H2 buffer.

Your problem was not the gas port size, it was the correct size to begin with.


What was wrong with the chamber exactly?

What gas block, tube, BCG/bolt, action spring and buffer was used? Is it absilutely certain that the gas block was perfectly centered over the gas port during assembly? Casey should have know that .071 was the correct size and likely not the culprit.

BTW when I say my 10.5 LMT, it's just the barrel that is LMT (maybe the H2 buffer but I lost track of which of my H2's are Colt or LMT in my AR's), everything else is an assembly of various MFG's parts to my liking. I measured the port myself to be .071".

 

[katazone]

I've shot thousands and thousands of MFS and Branaul crap through my 10.5 LMT and still do (that's basically all I shoot after I went through my crates of yellow box and white box Norinco and AE223), plenty strong ejection 10-12 feet away at my 4 oclock and that's with an H2 buffer.

Your problem was not the gas port size, it was the correct size to begin with.


What was wrong with the chamber exactly?

What gas block, tube, BCG/bolt, action spring and buffer was used? Is it absilutely certain that the gas block was perfectly centered over the gas port during assembly? Casey should have know that .071 was the correct size and likely not the culprit.

BTW when I say my 10.5 LMT, it's just the barrel that is LMT (maybe the H2 buffer but I lost track of which of my H2's are Colt or LMT in my AR's), everything else is an assembly of various MFG's parts to my liking. I measured the port myself to be .071".

Chamber was good. That was another guy.
Nothing out of the usual with this build. I have built several with no issue. I don't cut corners, I try to buy reliable MFG's parts.
The gas block was on proper.
I think I used Spike's ST-T1 in this one and regular power spring. Spikes full auto bolt. I swapped the set up with my good AR as I call her. Same issue.

That was the culprit. He took it apart twice. He re-ported it and this time this thing just runs like butter.
I'm no gunsmith but I'll take Casey's word.
The conversation of over gassing came up, we discussed, and he was careful not to go there.
I can't really tell you any more!

 

[Dietz]

Well that puzzles me... all things being equal you shouldn't have had a problem. Weird.

 

[katazone]

Well that puzzles me... all things being equal you shouldn't have had a problem. Weird.

Haha....well now you know why it was so frustrating this time for me. It was like


Casey saw a few of these Rainier manufactured barrels lately. That's what gave me the idea to share.

 

[Dietz]

Did you try it with a different BCG before sending it in?

 

[katazone]

Did you try it with a different BCG before sending it in?

Yea....did full swap with my reliable.
Anyways she's good now

 

[Leg]

The smaller port is used for 5.56mm NATO ammo as it runs higher pressures than .223. As a result it may have been under gassed for .223. That's why LMT advertises their 10.5" for NATO spec ammo only.

 

[Dietz]

The smaller port is used for 5.56mm NATO ammo as it runs higher pressures than .223. As a result it may have been under gassed for .223. That's why LMT advertises their 10.5" for NATO spec ammo only.

I see you kinda missed my post about me shooting thousands of underpowered crap through my 10.5 LMT.

 

[Leg]

No, I saw it. Glad you haven't had any issues. Despite your good fortune my point was that the OPs issue may be due to the ammo not meeting the design spec for the chosen gas port. I don't know what type of ammo Rainier had in mind or how they advertise that particular barrel. My point was simply that the spec may have been exactly what they intend it to be. Perhaps...

The "spec" for a MK18 gas port is exactly what the OP had originally. So it would seem to meet "mil spec" for a 10.5" barrel in military service used with NATO spec ammo. Otherwise manufacturers are free to manufacture to whatever spec they want. What is the spec? There isn't one, unless they're advertising it milspec, otherwise it's whatever they want. It can't be out of spec if that's the spec they chose. Starting to repeat myself, too much beer.