6mm ARC Short stroking

[Southern Custom]

I just built a 6mm ARC gas gun around an OdinWorks 18” barrel. It uses a rifle plus 2” gas system. This is built on an Aero Upper/Lower with Aero BCG. Carbine 3oz buffer and carbine spring. Gun is short stroking with the gas block fully open. Failure to strip a second round and failure to lock back on empty magazine. Mag functions flawlessly when cycled manually. I’ve never run this length gas system before so I’m a bit clueless. Anyone run into this issue?
And before you ask, the gas block isn’t clocked. I checked with bore scope. No blockage of any kind and I had it opened all the way. I did have a smidge of gas leakage forward of the block but not enough that it would worry me. Gun was well lubed. Also tried an Armaspec silent spring/buffer and no luck there either.
I thought I heard somewhere that these chambers are cut tight and that could possibly play a role in this. Just thought I’d check here before I go throwing money at lighter buffers and springs.
It’s a bummer to because the rifle is a tack driver 1 shot gun. Printing .5 with the first 20 rounds of Hornady 108ELD Match when I took it out for the first run today.

 

[TonyTheTiger]

If memory serves the Odin is rifle +1".
What is the gas port size? I've got a 22" rifle +2 with a pretty big port and if I did it again I would do +1 to get a bigger operational window. It was surprisingly finicky to set up, plenty of short stroking. As much as I like long gas systems I don't know if they're that necessary with this cartridge.

 

[Southern Custom]

It’s listed on other sites as rifle plus 2. Odin doesn’t list the length other than rifle XL.
Glad I’m not going crazy. Everyone wants to blame gas but that’s just not the deal here. You would thing Odin would make a recommendation for this kind of setup on their webpage.

 

[TonyTheTiger]

Looked up that barrel, it does appear to have a +2 gas length. Which puts it equivalent to a rifle gas 16" barrel but with even lower pressure at the port. Coupled with the short dwell time it sounds like a recipe for a cantankerous system.

 

[Dino11]

Odin barrels are +2 on the rifle length gas system, what length barrel do you have?

I have one of their 18" barrel with the +2 gas port. My gas port is .101 per the folks at Odin.

I was having the same issue as you, I think it is because the gas port is so close to the end of the barrel and does not give the gas enough time to fully cycle the BCG. I to was running my gas block fully open.

My rifle has a rifle length RE and stock, I called Odin to see if they had a fix for it and they stated they had only tested this system with a carbine length RE and buffer. So I was pretty much on my own to try and figure this out.

My fix for it was to remove 4 of the 5 steel wieghts out of the buffer and replace them with aluminum weights I made from 1/2" bar stock. This lowered the buffer weight from 5.2 oz to 3.4 oz, I then added a Wolff 10% reduced power action spring and all was good. I was able to adjust my gas block to almost closed position and the rifle is a very soft shooter. and because I am sending so little gas to the BCG the rifle barely gets dirty..

If I was you I would start with a reduced power buffer spring and see if that fixes your problem, you might want to try a different mag as well and don't fully load it. Try loading it with only two rounds and see if you get bolt lock on last round.

 

[oldfatguy]

Have you tried closing off the AGB and opening a little at a time? Could be bolt bounce instead of short stroking.

OFG

 

[Southern Custom]

Have you tried closing off the AGB and opening a little at a time? Could be bolt bounce instead of short stroking.

OFG

I’ve thought of this and I’ll experiment today but typically with bolt bounce I’m assuming a round would still be stripped.

 

[Constructor]

A +2 on an 18" is crazy to start with but the port size needs to be in the .100-.104 range. If you are trying to get it to cycle with starting loads(reloaded) that may be the problem. You need to run full pressure loads.

 

[SilencedShooter11B]

I think anything over rifle length on 6ARC is uncalled for really.

What’s your port size? With an 18” R+2”gas barrel it needs to be large

whag mags and what buffer weight are you using?

I just dealt with this a week ago with a 24” Craddock/Bartlein rifle+2 barrel

 

[Dino11]

Not sure if you are directing the question to me or the OP, but my port is .101. On an 18" barrel

Mags used are ASC, Duramag, and Amend 2. All mags work flawlessly. Since the modifications not one problem, and the rifle shoots very smooth. I can watch the hits through the scope, sight never leaves the target.

 

[Southern Custom]

Just got back from the range and problem solved. I yanked the Odin gas block and found I was getting a ton of leakage around the tube and barrel both. The block was a really loose fit. I grabbed a new Aero fixed block I had in the parts bin and the fit was much tighter on both barrel and tube. I also grabbed the lightest bolt carrier I had and installed it.
I hit the range tried it with a lighter buffer and shorter spring and it ran fine. I switched back to a 3oz buffer and standard carbine spring and again, it ran flawlessly. This tells me the gas block was simply dumping gas. I did try an Armaspec quiet buffer and it locked on the carrier body, not the bolt. So it’s definitely on the edge of running well. I have a reduced power spring on the way.
other than that it cycles nicely and recoil is mild. Looks like it will hold .5 MOA with Hornady Factory 108 Match and I’m getting around 1630 after 40 rounds of break in. Time to move on the the reloadingbench and see what we can do. SD with the Factory 108s is right at 9. Impressive stuff.

 

[Dino11]

I posted this a while back, this worked for me rifle runs 100% now. I had every kind of malfunction you can imagine, feeding, firing, and ejecting.

Odin barrels are +2 on the rifle length gas system, what length barrel do you have?

I have one of their 18" barrel with the +2 gas port. My gas port is .101 per the folks at Odin.

I was having the same issue as you, I think it is because the gas port is so close to the end of the barrel and does not give the gas enough time to fully cycle the BCG. I to was running my gas block fully open.

My rifle has a rifle length RE and stock, I called Odin to see if they had a fix for it and they stated they had only tested this system with a carbine length RE and buffer. So I was pretty much on my own to try and figure this out.

My fix for it was to remove 4 of the 5 steel wieghts out of the buffer and replace them with aluminum weights I made from 1/2" bar stock. This lowered the buffer weight from 5.2 oz to 3.4 oz, I then added a Wolff 10% reduced power action spring and all was good. I was able to adjust my gas block to almost closed position and the rifle is a very soft shooter. and because I am sending so little gas to the BCG the rifle barely gets dirty..

If I was you I would start with a reduced power buffer spring and see if that fixes your problem, you might want to try a different mag as well and don't fully load it. Try loading it with only two rounds and see if you get bolt lock on last round.

 

[Cotay]

Just got back from the range and problem solved. I yanked the Odin gas block and found I was getting a ton of leakage around the tube and barrel both. The block was a really loose fit. I grabbed a new Aero fixed block I had in the parts bin and the fit was much tighter on both barrel and tube. I also grabbed the lightest bolt carrier I had and installed it.
I hit the range tried it with a lighter buffer and shorter spring and it ran fine. I switched back to a 3oz buffer and standard carbine spring and again, it ran flawlessly. This tells me the gas block was simply dumping gas. I did try an Armaspec quiet buffer and it locked on the carrier body, not the bolt. So it’s definitely on the edge of running well. I have a reduced power spring on the way.
other than that it cycles nicely and recoil is mild. Looks like it will hold .5 MOA with Hornady Factory 108 Match and I’m getting around 1630 after 40 rounds of break in. Time to move on the the reloadingbench and see what we can do. SD with the Factory 108s is right at 9. Impressive stuff.

Yours is not the first time I've seen this reported with Odin's Tunable Gas Block that is included with their barrels.

 

[Teetop]

I just built one my self with 18" xl 6mm arc. Mine feeds fine just does not lock open, 3 Oz buffer has bolt bounce and 4.6 Oz lock open on bolt carrier. Talked to odin yesterday and he said try 3.8 Oz and adjust gas block as required. He told me that earlier production barrels had under sized gas holes but have in the last year be corrected, gas hole should be .106 per odin. Odin Also told me full open on gas block is where lock set screw has 2.5 to 3 threads protruding. Also told me do not go further than the 2.5-3 because it will not work right either.