Ejecting but won't lock back on last round

[hound53]

21 inch Criterion barrel chambered by Precision Firearms, Aero receiver, bolt group, and adjustable gas block. Tried 105 gn and 90 gn bullets. AC 2560, and LeverEvolution powders workups. Gas block is now at full open and has been removed and checked a few times. I am using ASC 5 and 10 round magazines and also a 6.5 Bobsled single feed. The bolt has locked back maybe 3 times out of 300 or so rounds, Cases eject from 4 o'clock to 3 o'clock depending on powder load and gas block setting. Magazines and lower work fine on two separate rifle length 6.5 Grendel uppers and a rifle length .223. I also tried 2 other bolts from my Grendels and waxed the bolt contact areas in the upper. The bolt drops in easily and does not seem to be hanging on the gas tube. I am running out of ideas here and about ready to either enlarge the gas port (last resort), try a non adjustable gas block, get another lower and with a lighter buffer spring or pull the barrel and gas tube and install on another upper.

All suggestions welcome and thanks in advance

Jim

Oh and as a side note I ran into a buddy at the range who is having the same problem with his 6 ARC build. I have no idea what his build is but he is also a experienced AR builder. Is this a common problem with this cartridge?

[pmc847]

I had same problem.    https://6mmarc.com/showthread.php?tid=778
 Ended up removing weight from buffer until reliable lock back.  Running Superlative adj gas block with rifle +2.

I also run a 223/556 upper 20" SLR adj gas block/ rifle length and have to swap buffer/ spring to accommodate. 

Philip

[grayfox]

What does it do with factory 105's and/or 108's?

I have/have had 4, 6Arc barrels (still have 3, 16, 18, 20 and bolt-action) and none of them have this issue. All shoot 90, 100, 103, 105 and 108's. Basically (and I am not an expert here) I'd say undergassed or over-buffered or under powdered. Pardon the grammar. You don't say what stock/spring/buffer you're using. A rifle stock setup, IMO is a no-no, no matter what it does for other calibers. I stay with carbine systems.

I did have 2 223-wylde barrels that I had to enlarge the port on, and now they run fine.
There are a couple of tricks you'd want to do if you go that route.

But first, before you mod the barrel, I would contact Mark back at precision firearms to see what he thinks, he's busy but reliable and might have some ideas for you, even take it back to look at maybe.

[hound53]

Thanks for the suggestions. I have not tried any factory ammo. I am using a H2 buffer and rifle length spring. Pretty sure I can rule the ammo out, I have been reloading for gas and bolt rifles for 20+ years and the chrono data is showing the expected FPS.

I am 99% sure it is not the barrel knowing PF's reputation for quality work and testing all their barrels. I figure it is something on my end and after ensuring myself that the bolt is not binding or catching that leaves the gas system and the buffer assembly. I have removed and replaced the gas block and tube twice now to make sure the alignment and position was correct and all three Grendel bolt carriers will drop into place with no binding on the gas tube

Since my lower works perfectly will my Grendels and .223 uppers I have decided to put together a new lower using a carbine length buffer and spring. I will update the thread after I test it hbut I really do think that will do the trick

[TonyRumore]

In the last 15 years or so, the train has completely jumped the tracks with the gas systems being extended too far down the barrel.
So you end up trying to cycle the BCG with a super sharp quick blast of gas running through an excessively large gas port.
And why do we do that? Because the 3-gun game boys figured out the recoil impulse was less. But what about running the gun's system/design in the sweet spot, rather than out on the fringe of the operating window?

I don't know about you, but I would prefer to not run my bullet over a huge one-sided pot hole in the barrel when it could be much smaller with the gas system backed up a bit.
And another thing. Giving up a pile of case capacity so you can dangle the bullet way out past the neck of the case so it looks cool, is just a bad idea. Not to mention the leverage that is imparted on that dangly bullet as it tries to transition from the magazine to the feed ramp to the chamber. Talk about some bullet run-out.

Tony Rumore
Tromix

[sundowner]

Had the same problem with mine at first but I had a Rubber City armory adjustable BCG , put in a standard BCG and a 3OZ buffer and the problem disappeared .

[hound53]

Major oopsies on my part. Yesterday pulled the buffer and weighed it and found it is a carbine buffer at only 2.9  oz. Since that lower runs fine with my other upper I went down to the local Palmetto Armory an picked up a new lower and have a Odin Works adjustable buffer on the delivery truck. Just guessing here but I think my reasoning was 180 out and a heavier buffer might cause the BCG to travel farther backwards due to inertia. I should be able to test that theory Saturday or Sunday.

Not related to this thread but I am impressed by that low cost lower. It is every bit as tight on  the uppers as my Rock River match lower. The trigger is smooth with no take up and a nice crisp reset. A bit heavy but I won't decide on whether to replace it with a two stage unit until I test it in live fire.

[pmc847]

Major oopsies on my part. Yesterday pulled the buffer and weighed it and found it is a carbine buffer at only 2.9  oz. Since that lower runs fine with my other upper I went down to the local Palmetto Armory an picked up a new lower and have a Odin Works adjustable buffer on the delivery truck. Just guessing here but I think my reasoning was 180 out and a heavier buffer might cause the BCG to travel farther backwards due to inertia. I should be able to test that theory Saturday or Sunday.

Not related to this thread but I am impressed by that low cost lower. It is every bit as tight on  the uppers as my Rock River match lower. The trigger is smooth with no take up and a nice crisp reset. A bit heavy but I won't decide on whether to replace it with a two stage unit until I test it in live fire.

I have a Geissely SSA trigger with 3 sets of springs to tune  to your preference.  High Speed Match, SSA E and Stock.  
Also Harris SBRM With S lock adapter and American QD piccatiny adapter.

Just in case you want to upgrade.  

Cheers
Philip

[hound53]

Major oopsies on my part. Yesterday pulled the buffer and weighed it and found it is a carbine buffer at only 2.9  oz. Since that lower runs fine with my other upper I went down to the local Palmetto Armory an picked up a new lower and have a Odin Works adjustable buffer on the delivery truck. Just guessing here but I think my reasoning was 180 out and a heavier buffer might cause the BCG to travel farther backwards due to inertia. I should be able to test that theory Saturday or Sunday.

Not related to this thread but I am impressed by that low cost lower. It is every bit as tight on  the uppers as my Rock River match lower. The trigger is smooth with no take up and a nice crisp reset. A bit heavy but I won't decide on whether to replace it with a two stage unit until I test it in live fire.

I have a Geissely SSA trigger with 3 sets of springs to tune  to your preference.  High Speed Match, SSA E and Stock.  
Also Harris SBRM With S lock adapter and American QD piccatiny adapter.

Just in case you want to upgrade.  

Cheers
Philip

only competition I will do with this is AR tactical prone (20 rounds in 20 min) nothing rapid fire. Too much metal in my leg for run and gun stuff. So as long as the trigger is clean and crisp I am good to go. I ahve not put a gage on it but just guessing I am thinking it's about 4 -5 lbs.

Way offtopic but the reason I decided to give the PA lower a chance was this year a buddy won the mid range 600 yard club championship shooting a bone stock PA in .223 Rem. He shot 3 cleans for a perfect 600 score. I forget how many X's but he came damn close to setting a national record with that rifle. He beat my Wilson Combat barreled upper on a Rock River match lower 6.5 Grendel as well as several other competitors using high dollar AR's. As my daddy said it ain't so much the arrow as it's the indian holding the bow

[pmc847]

I have a PF PF Enterprise V in 223 Wylde 20" .875.
Also a PF side charge upper with 6ARC 26" .930 rifle +2.  same lower.
I also had cycling problem with the 223, rifle length.  Ended up being buffer spring.  I did send it in and Mark claimed they incorrectly installed a 308 spring. Fixed and runs flawless.  The 6ARC different story.  Had to completely remove all the buffer weights to get it to run reliably. 

I agree, your buddy's analysis is right on.

By the way the Qeisslele brakes at 2 lbs with the Match springs.  Sweet trigger.  I now have a TriggerTech Diamond that breaks at +-1.5 lbs.  Got a great deal that I couldn't pass up.

Philip

[hound53]

for AR tactical prone I can't go below 4.5 lbs on  the trigger.

[Dino11]

The way I'm reading you running a rifle buffer spring with a carbine buffer?

A rifle spring is longer than a carbine spring.

[grayfox]

Longer and a bit stiffer too I think.
Yes I read that also come to think of it, so don't know if that is what the OP meant or not...

If you want to use a rifle stock but have a carbine-interior "setup" there's a poly "insert" you can get to go behind the carbine spring and buffer weight, that shortens the rifle stock's effective tube length. I have that for one of mine b/c I got a deal on a rifle butt stock - but the rest are carbine style...

A carbine buffer won't cycle a rifle spring.

[hound53]

I was mistaken on both the spring and buffer weight in my first post , both the buffer and spring are carbine. Sorry for the confusion, it was carbine length spring and a 2.9 oz buffer.

Over the weekend i removed and replaced the gas block and tube and used a borescope to make sure the gas block hole was correctly aligned. The Odin Works adjustable buffer came in, later today I will be experimenting with different weight combos one at a time. I also loaded up some 107 SMK's just to see if a slower bullet/powder combo might help. I did notice that the barrel in front of the gas block (Aero low profile adjustable)looks as if it is getting some blow by. I may try a non adjustable .

[pmc847]

I just ordered a carbine length Odin adjustable buffer and flat wound spring.
The weather up here is in single digits and windy, the dog won’t even go outside. I guess I’ll do some reloading in the meantime.

Cheers

[Dino11]

You could also get a reduced power buffer spring, that's what I had to do with mine. I also removed 3 of the 4 tungsten weights in my buffer and replaced them with some 1/2" aluminum bar stock I got at Home Depot. That took a couple ounces out of the buffer.

But I'm comparing apples to oranges as I have a rifle length buffer system in mine. Now my gas block is almost closed and sends very little gas back to the BCG, and literally has almost zero recoil.

[pmc847]

That's interesting. I have rifle length with no weight in the buffer and stock spring. Gas wide open. I will use the spacer from my JP captured spring buffer that I use with the 223 so I can use the carbine buffer setup. I would like to get the gas block somewhere in the middle so I have some adjustability.

[Dino11]

That rifle has an 18" Odin barrel on it with a +2 gas port, Everybody told me I would never get that one to cycle because of gas port location, the gas port in that gun is huge @ .101

This was one of the first rifles to come out of their shop, only them and Barrett were making them back then. At the time Barrett was only making Military contract stuff, Odin told me that nobody was using a rifle length system, I was the first one to try it. They never even tested one.

I just got lucky thinking outside the box and did what everybody told me wouldn't work. And that rifle is a tack driver shooting .5 MOA

[hound53]

today it locked back on the first firing with no buffer weights at all installed, the next five firings were no joy. That was with a 107 gn bullet at the top of the recommended load Power Pro Varmint, 27.4 gns with CCI 450 primers. Tried testing with a magazine and will not feed reliably. I am looking hard at the gas block and gas tube now. It is the only thing left

[Dino11]

Exact same problems I was having... Get a reduced power buffer spring, they are easy to find for carbine length. Not so easy for rifle length.

I have the Odin block in mine.  Shoot some Brake Clean down the gas tube from the chamber end and see if it comes out the end of your barrel. Then take out the set screw and adjustment screw and make sure their is no debris in it. You do realize their are two screws in that hole, Another thing to check is most high end barrels want you to seat the gas block all the way back against the gas block shoulder, not spaced away from it for a hand guard mount ring.

Maybe I should ask which gas block you have? They have a couple different styles of them.