cycling issues with my first 308 build

[808chx.irradicator]

     I've read some of the posts on this issue already but thought I'd check with everyone first before acting. First off let me give you the components in question: 22" Criterion hvy hybrid barrel, non-adjustable Ballistic Advantage gas block, rifle length Rosco gas tube, Fulton Armory bcg, Aero Precision enhanced upper and M5 billet lower, rifle length tube (don't remember who from) and the Armalite buffer and spring. The gas port on the barrel is .075", the gas tube is half way down the cutout, the internal depth of the tube is 9 3/4", spring length is 13 1/2", and buffer is 5 1/4" at 5.35 oz. If it matters I'm running the LaRue mbt trigger.

     So my issues are that it'll fire, but won't eject the case properly, and the bolt won't lock back at all. Its as if it's under gassed. I've only fired 12 rounds through it so far, and thats feeding the rounds in individually. After reading up on this my guesses are that possibly the gas port needs to be opened to at l east .085 - .090, or that maybe I'm running the wrong buffer tube length. I mean, if the port size is .0750 maybe I should be running a carbine system? I've also read that maybe I need to run it extremely wet, which I haven't done. The fulton bcg fit to the criterion extension is REALLY tight! Sometimes I really have to pull hard on the charging handle to get that thing out of battery.

     Any thoughts? I'd rather try the carbine length tube first before drilling the barrel to see if that does anything. Well, I guess first I'd like to try lubing the hell out of the bcg and see if that does anyting. Open to any suggestions! Thanks

Edited September 2, 2021 by 808chx.irradicator

[98Z5V]

What ammo are you running through this thing?  Lets start with that.

[98Z5V]

31 minutes ago, 808chx.irradicator said:

I've only fired 12 rounds through it so far,

 

31 minutes ago, 808chx.irradicator said:

I've also read that maybe I need to run it extremely wet, which I haven't done.

^^^  Those are two things working against you, right off the bat.  You can fix one, easily, and that's "Lube it UP!"  Heavy.  You can't fix the 12 rounds-issue, and sealing the gas block t the barrel, gas tube to the gas block - that's carbon fouling that does that.  You could do the Loc-Tite thing that alot of people swear by, but I personally thing that's stupid. As fuk.  Shoot the gun to seal those small ports - let it do what it's supposed to do.

[edgecrusher]

Also, did you have your bolt headspaced to the barrel? 

[808chx.irradicator]

20 hours ago, 98Z5V said:

What ammo are you running through this thing?  Lets start with that.

@98Z5VThanks for the responses/help. Ammo? The only kind I could find, Win. 7.62x51 149 grain M80 fmj. I agree with the carbon fouling over loctite as far as sealing the gas system. I've torn the rifle all apart to check things out but I think I'll put it back together and lube the hell out of the bcg and see what happens.

Edited September 3, 2021 by 808chx.irradicator

[808chx.irradicator]

13 hours ago, edgecrusher said:

Also, did you have your bolt headspaced to the barrel? 

@edgecrusher At the time I bought the barrel no JP or Fulton bolts were available so I didn't get that option with Criterion. I purchased the complete bcg from Fulton separately and have reached out to Criterion about maybe sending it to them for headspacing, but haven't heard back from them. Since they sell Fulton bolts on their site I thought it wouldn't be a problem. I was thinking maybe I'll use a little Flitz and polish the lugs on the bolt and extension to see if that'd help??

Edited September 3, 2021 by 808chx.irradicator

[dpete]

A good gunsmith that knows what he is doing will be able to headspace your bolt for you.  You need to remove the ejector first.

[98Z5V]

Just now, 808chx.irradicator said:

@98Z5VThanks for the responses/help. Ammo? The only kind I could find, Win. 7.62x51 149 grain M80 fmj.

What brand?  Some are good, and some suck.   Don't sweat this too much - we'll get this gun running.  Major parts accounted for, it's got solid operational gear. 

[808chx.irradicator]

4 hours ago, 98Z5V said:

What brand?  Some are good, and some suck.   Don't sweat this too much - we'll get this gun running.  Major parts accounted for, it's got solid operational gear. 

@98Z5VSorry, Winchester brand. You know, the white box with red lettering and cowboy on it. They look like old stock cause the casings were really discolored, like they could've been previously fired. Yeah I believe the components are good, just need to figure out what the issue is. But on the good side my first 3 shots out of this rifle were really good, 2 rounds right on top of each other and the 3rd just right a bit, all fitting under a nickel and that was with a crappy 1-6 scope at 100 yds. So I have high hopes.

Edited September 3, 2021 by 808chx.irradicator

[808chx.irradicator]

6 hours ago, dpete said:

A good gunsmith that knows what he is doing will be able to headspace your bolt for you.  You need to remove the ejector first.

@dpeteIf I had go/no-go gauges I'd do it myself but for right now I'm not thinking it's the headspace...but we'll see 🤷‍♂️

[jtallen83]

6 hours ago, 808chx.irradicator said:

If I had go/no-go gauges

They won't cost that much more than shipping the barrel back and forth to Criterion, then you have them for the next build. 

I wouldn't mess with the lugs, they will mate up with their partners pretty quick from just rounds down range. Lube it up and run a couple boxes, start out one round at a time hoping for lockback then load it up as it starts to function. That's all quality parts so expect her to be a little tight to start. 

[808chx.irradicator]

3 hours ago, jtallen83 said:

They won't cost that much more than shipping the barrel back and forth to Criterion, then you have them for the next build. 

I wouldn't mess with the lugs, they will mate up with their partners pretty quick from just rounds down range. Lube it up and run a couple boxes, start out one round at a time hoping for lockback then load it up as it starts to function. That's all quality parts so expect her to be a little tight to start. 

@jtallen83  Thanks, that's what I've decided to do. "expect her to be a little tight to start" 😂😂😂 yah... I been looking for some 308 gauges but I guess they're a hot item, hard to find those damn Clymers

[808chx.irradicator]

Some recreated pics to show what I was dealing with at the range. After every fired shot this would happen. The case would fall back in when locking the bolt to the rear, and then I tip the rifle to get it out, load another one and so on.

[808chx.irradicator]

Also here's some pics of the buffer tube ID and the gas tube looking in from magwell.

[808chx.irradicator]

Ran into something else. Don't know if it's important or not but thought I'd show it anyway. In inspecting the spent casings further I noticed 2 vertical scratches and between the scratches at the case opening its flattened out. The picture doesn't really show it very well, but in person its noticeable. My first guess would be the feed ramps? I'm sure the collective knowledge on this forum will know a lot more about this than me. I've built 'many' ar15's with practically no issues, so this is a first for me, but was expected in reading up on building 308's.

[98Z5V]

Receiver extension is the required 9 11/16" internal, on the money.  Buffer should be 5.200" long and weigh 5.4 oz.  Recoil spring should be 100% identical to the Armalite AR-10 EA-1095 spring.  No other substitutes. Dimensions of that spring can be found on HeavyBuffers.com, in their "reference" link.

Gas tube is the right length. 

What's your gas port diameter in the barrel?

[808chx.irradicator]

20 minutes ago, 98Z5V said:

Receiver extension is the required 9 11/16" internal, on the money.  Buffer should be 5.200" long and weigh 5.4 oz.  Recoil spring should be 100% identical to the Armalite AR-10 EA-1095 spring.  No other substitutes. Dimensions of that spring can be found on HeavyBuffers.com, in their "reference" link.

Gas tube is the right length. 

What's your gas port diameter in the barrel?

@98Z5V The gas tube, spring, and buffer are all Armalite. Buffer weighing in at 5.35oz. The gas port on the barrel is .0750. In reading up on this in other posts its mentioned that the port size should be between .085-.095. But before I go doing that I think I'm gonna run the rest of the box and the 2 others I have with it well lubed first to see what happens.

[98Z5V]

40 minutes ago, 808chx.irradicator said:

@98Z5V The gas tube, spring, and buffer are all Armalite. Buffer weighing in at 5.35oz. The gas port on the barrel is .0750. In reading up on this in other posts its mentioned that the port size should be between .085-.095. But before I go doing that I think I'm gonna run the rest of the box and the 2 others I have with it well lubed first to see what happens.

Gas PORT DIAMETER IN THE BARREL, or is that the gas block journal size?  The size of the gas block that you have to fit over the barrel?.  I'd like for you to link those other posts that you've referened, right here in your thread, below.  I'll look at them.

On 9/1/2021 at 7:56 PM, 808chx.irradicator said:

     I've read some of the posts on this issue already but thought I'd check with everyone first before acting. First off let me give you the components in question: 22" Criterion hvy hybrid barrel, non-adjustable Ballistic Advantage gas block, rifle length Rosco gas tube,

So, barrels details are necessary, and it's necessary that they're accurate...    22" Criterion barrel.  Got it.  Rifle gas system.  Got it.  What's the gas block journal diameter on the barrel, and what's the gas port diameter IN the barrel?

the numbers you threw up there are kinda all over.  0.085"~0.095" covers everything in a 0.750" journal diameter from 18" midlength gas .308 Win all the way up to 18" and 20" rifle gas .308 Win. 

details are important.  If you're on rifle gas, 22" .308 barrel, you're gonna need to be on the small side of some of the numbers that you've posted.  Pending journal size, of course.

 

What size was that BA non-adj gasblock that you bought?  It's either 0.625", 0.750", 0.875", or 0.936".  BA doesn't make two of those sizes, so...   that will answer the journal diameter question.  Only other question is what size gas port did Criterion put in that 22" rifle-gas barrel?...

Don't sweat it - we'll get this gun running.  It just takes accurate details to figure out what needs to be done to it, if anything. 

Edited September 5, 2021 by 98Z5V

[808chx.irradicator]

1 hour ago, 98Z5V said:

Gas PORT DIAMETER IN THE BARREL, or is that the gas block journal size?  The size of the gas block that you have to fit over the barrel?.  I'd like for you to link those other posts that you've referened, right here in your thread, below.  I'll look at them.

So, barrels details are necessary, and it's necessary that they're accurate...    22" Criterion barrel.  Got it.  Rifle gas system.  Got it.  What's the gas block journal diameter on the barrel, and what's the gas port diameter IN the barrel?

the numbers you threw up there are kinda all over.  0.085"~0.095" covers everything in a 0.750" journal diameter from 18" midlength gas .308 Win all the way up to 18" and 20" rifle gas .308 Win. 

details are important.  If you're on rifle gas, 22" .308 barrel, you're gonna need to be on the small side of some of the numbers that you've posted.  Pending journal size, of course.

 

What size was that BA non-adj gasblock that you bought?  It's either 0.625", 0.750", 0.875", or 0.936".  BA doesn't make two of those sizes, so...   that will answer the journal diameter question.  Only other question is what size gas port did Criterion put in that 22" rifle-gas barrel?...

Don't sweat it - we'll get this gun running.  It just takes accurate details to figure out what needs to be done to it, if anything. 

@98Z5V Ok, I just put her back together today and don't want to tear her apart and take pics to answer these questions so I'll do my best. The gas block journal size on the barrel is 0.875, and that's the size of the internal diameter of the BA non-adjustable gas block. The gas port diameter IN the barrel is...actually let me go take a pic

[808chx.irradicator]

15 minutes ago, 808chx.irradicator said:

@98Z5V Ok, I just put her back together today and don't want to tear her apart and take pics to answer these questions so I'll do my best. The gas block journal size on the barrel is 0.875, and that's the size of the internal diameter of the BA non-adjustable gas block. The gas port diameter IN the barrel is...actually let me go take a pic

ok, as per my Frankford Arsenal calipers, the gas port diameter in the barrel is 0.075" hopefully that clears up my numbers confusion.

[808chx.irradicator]

1 hour ago, 98Z5V said:

Gas PORT DIAMETER IN THE BARREL, or is that the gas block journal size?  The size of the gas block that you have to fit over the barrel?.  I'd like for you to link those other posts that you've referened, right here in your thread, below.  I'll look at them.

@98Z5V Um, how do you do that? Kinda new to forums so... let me look

[808chx.irradicator]

4 minutes ago, 808chx.irradicator said:

@98Z5V Um, how do you do that? Kinda new to forums so... let me look

Found it. The title of the post is "LR-308 won't cycle. Please help so I don't have to pay my gunsmith any more money" posted by Mrj209. In that post is where I learned about really lubing it up and opening up the gas port diameter in the barrel. You were actually the one to mention it.