It doesn’t matter what they say. With the barrel as is from the factory the rifle didn’t work with the port that is in it. Manufacturers of 308 AR barrels drill them too small on such a routine basis that its laughable. They drill the port too small so they can TRY to get away with a buffer that is too light (3.8 oz) to allow the gun to function as it should with any ammo you want to throw at it.
The OP already has the proper buffer tube/recoil system, and the proper length gas tube and yet the rifle doesn’t function. That only leaves the gas system and his gas block is fine. His port is too small to allow enough gas into the system for the rifle to work. Using AR15 logic and knowledge with a 308 AR doesn’t work in most cases. THEY ARE NOT THE SAME. Most manufacturers don’t know or don’t care about the differences between an AR10 and a 308 AR. An AR10 is a 308 AR, but all 308 ARs are not AR10s.
I know the’re not the same as AR-15s. I’ve “built” three 308 ARs.
The barrel manufacturer screwed up, so they should be informed of the situation and be held accountable, not the end user.
I completely agree with you. The problem is if they drill all of their 18" rifle gas barrels to that size because that is their spec. anyone the OP speaks with will say the hole is correct and will work. That leaves him to go back and forth for who knows how long trying to get them to make it right, or go the route with the fewest headaches and fix it himself.
if you can remember how to use pie-R-squared, you can calculate the gas-port cross-sectional area, which represents gas flow potential.
if your existing gas port is .0770", then a #43 .0890" is a 34% increase in gas flow, and a #41 .0960" is a 55% increase.
Grizz, what manufacturer says is in the thread. Michael at Criterion was quite surprised. I think at first he thought warn machining till he heard the numbers. Then he just said “yeah, that’s way undersized”. Wanted me to send the complete upper back so he could verify everything he heard from me. Can’t blame him for doubting someone who may or may not have just fell off the turnip truck.
rpol98, thanks for the figures. There is a table in the links dpete provided which indicates as much. I didn’t add up the increments (%ages are provided at each step as drill bit size increases) but I could see it was over 40% at a glance. Good reading in those two links!
If Criterion asked me to send in an upper, I’d send in the upper.
We’re not talking about some cheap disposable barrel from a company that doesn’t give a shit about quality.
I’ve been waiting on one of their barrels to become available for many months.
Well its obe’d now. After anguishing over it I find as promised it was a piece of cake. Not that I didn’t make a bubba project out of it. Was determined to use a press rather than freehand with a drill. But my little table is too small to stabilize an upper. Didn’t want to pull the barrel so like putting a ladder on step-stools I bubba’d something precariously stable and like suggested ran the .0770 bit till I was centered. I used a brass rod rather a wood dowel for backstop. Worked like a champ. You might respect me less after watching this:-))). That is if the link works.
The link works and you did what you had to do to get the job done. Well Done! Now put her back together and go shoot. Start with the gas block wide open, however many clicks that is until your done with a break in.
Awesome, make sure you follow up and let us know how it runs!
Will do! Got a family reunion starting tomorrow. Maybe the heat will be tolerable the week after. Sure appreciate all the helpI got here!
Function problem resolved! Thanks for the help!!
The bolt locks back on empty. Bolt stripped cartridges from magazine just fine, at least while cycling under fire. I didn’t spend a lot of rounds since all I have is expensive Federal Gold Dot, but shot 10 rounds with none of the previous issues.
I appear a little over-gassed judging from brass angle (2 o’clock), at least running with the Superlative wide open and 168gr ammo. I tuned the Superlative down a couple clicks at a time after each shot till I was throwing at 3 o’clock. Took six shots. Then I shot a four shot group. I don’t know how this setting would disperse brass from say 150gr - guess I’ll find out after I buy and load some.
I did have one issue I don’t fully understand. If I release the bolt with the bolt release the round hangs. If I pull the charging handle back the full distance and release the round feeds fine. Its like that extra run at the bolt from the added spring tension is needed. And like I said above the bolt strips and chambers just fine after each shot.
Nice! It’s a great feeling when a problem is solved. As to your issue with the round hanging, are you sure that when the bolt is locked back that the bolt release is catching on a bolt lug and not the carrier face?
George, Good catch. I just checked and think that might be exactly what I was doing. Thnx!
Was your issue with the bolt happening with the gas block wide open or partially closed? If it was happening with it wide open it would be something to worry about. If it began happening after you partially closed the gas block to adjust the pattern, you may have created the issue. Being overgassed or undergassed causes 308 ARs to not function. If it was fully functioning with the bolt feeding rounds from any release point with the gas block wide open you have nothing to worry about. As long as bullets properly load and empty brass makes it out of the ejection port, it is a perfectly and fully functioning rifle. Ejection pattern is meaningless in a 308. Weaker loaded bullets will not eject to the same angle as hot loaded bullets.
you want to tune the gas block so that you get enough gas to consistently lock the bolt back when the mag runs dry, “last round bolt hold open”. That’s your prime tuning criteria.
bolt face behind the bolt catch, not the bolt carrier on the bolt catch, and not the bolt face on the mag follower. these last 2 are faulty situations resulting from insufficient gas.
As for ejection pattern. Read down into the comments specifically about ejection. Those guys know more about 308 ARs than anyone else, including most manufacturers.
https://forum.308ar.com/topic/24277-update/
Double post
Ok, the problem I identified was what George caught. In other words, operator-error with a ‘manual process’. That occurred because I was manually clearing and making the weapon safe while I adjusted the gas block between each shot. All that was on me. When cycling under fire everything operated as you’d want. My manual operation suffers - mostly from 45 yrs since handling the M-16.
I appreciate the link on ejection pattern with a .308. Was not aware the difference between the AR-15 and the .308. I’ll be sure to read all that. I need to head over to that site with some ammo questions anyway. Btw, on a related note, my M1A flings back hard enough to dent brass on the deflector. That might be some interesting research as well.
Good to know you got it figured out and it wasn’t a difficult catch.
Glad you got it figured out. Now go enjoy!