6.5 Creedmoor gas length question

[Smitty192]

How important is the +2 gas system on a 6.5 Creedmoor large frame AR? What will the downside be of using a rifle length gas system?

Thanks

 

[padom]

Very important. Downside is blown primers and brass getting beat up pretty bad

 

[Smitty192]

Thanks. Most of the 6.5 barrels I see for sale are only rifle length. Wasn't sure how imperative it was.

 

[padom]

Rainer Ultramatch (Shillen blank) 6.5cm with +2 gas was on sale the other day. Might still be...

 

[mpk1996]

its also has to do with the length of the barrel. so, if you were to say have a 18-20" barrel, the dwell time would be similar to that of a +2 system on a 24" barrel. its this dwell time that causes excessive gas to get back to the bolt. a lot of that can be mitigated with an adjustable gas block or smaller gas port. but in high pressure cartridges like the 6.5 CM, you can only regulate it so much before the bolt will not function. the idea of the reduced dwell length has as much to do with delaying unlocking as it does with overpressure. this should help with "accuracy." that way there is little to no movement of the bolt/BCG while the bullet is still in the barrel

 

[Smitty192]

Thanks MPK. Delaying unlocking the bolt makes sense. All I could find with a +2 gas system is JP. Do you know of any others?

Thanks

 

[jeremyp]

Proof Research also has +2 gas systems on their 22" & 24" 6.5 Creedmoor barrels. Ranier also offers the Ultramatch with +2 gas system.

 

[Smitty192]

Awesome, thank you for the heads up.

 

[The King]

I will add to this - a gas pressure curve for rifle barrel tapped gas has 3 critical aspects:

1. How long the bullet has been in the barrel before gas begins to flow into the operating system.
2. What the pressure of the gas is as it enters the operating system.
3. How long the dwell time is after the bullet has passed the gas port.

So it is true that a +2 gas system on a 22" barrel has similar dwell times to a 20" barrel with rifle gas, the +2 gas system will have a lower port pressure as well as more time between cartridge ignition and bolt opening. I would wager that a 22" or 24" +2 barrel is more reliable in every way than a 20 or 18" barrel with rifle gas.

Adjustable gas blocks can mitigate the pressure issue but not the other two.

 

[Smitty192]

Forgive my ignorance on the subject....a 20" barrel with a rifle length gas system would be good to go?

 

[The King]

It would not be as preferable as a 22" with +2, and not as bad as a 22" with Rifle.

 

[Smitty192]

I see Rock River has a LAR8 in 6.5 Creedmoor now. It only has a 20" barrel (rifle length gas system) and uses the same bcg as the LAR8 (308). No high pressure bolt I had a LAR8 Varmint that was lights out. Not sure about the 6.5 CM. Although, it would be tempting.

 

[The King]

If I were to buy a new 6.5 gasser I would wait for the savage MSR-10. It has +2 gas, side charger, small form factor...lots and lots of goodness up in there it seems. Of course, there are 0 reviews because it isn't out yet, but I consider it worth the wait and will get one.

 

[Smitty192]

I have been looking at that rifle. Looks good on paper, for sure.

 

[DavidAR10]

It would not be as preferable as a 22" with +2, and not as bad as a 22" with Rifle.

 

[elfster1234]

the main key is the adjustable gas block more than anything.. i have a custom made from the ground up mega 6.5 AR with a 22" barrel with an extra 2" gas and IMO it makes for a super smooth shooting AR and is my crown jewel in my collection... with the custom brake = shoots damn near like a .223... i was in the middle of making a complete series on my MEGA 6.5 creedmoor when i found out about my whole cancer ordeal..... which i hope to pick up soon late spring

part#1 direct link: https://www.youtube.com/watch?v=mBCLSxytkeM


part#2 direct link: https://www.youtube.com/watch?v=_N_m2g8jlho

 

[The King]

Damn. We should make this the "anything is fine as long as it isn't Cancer" thread.

I literraly just got back from the doctor where he told me he finally has enough information to tell me I probably managed to pick up a slight case of it myself. Something along the lines of "you don't just catch seizures like a common cold at the age of 40 son...you either are born with em or you got trouble coming..."

I knew that last hooker on the road out of TJ was a bad idea but damnit you only live once...

the main key is the adjustable gas block more than anything.. i have a custom made from the ground up mega 6.5 AR with a 22" barrel with an extra 2" gas and IMO it makes for a super smooth shooting AR and is my crown jewel in my collection... with the custom brake = shoots damn near like a .223... i was in the middle of making a complete series on my MEGA 6.5 creedmoor when i found out about my whole cancer ordeal..... which i hope to pick up soon late spring

part#1 direct link: https://www.youtube.com/edit?o=U&video_id=mBCLSxytkeM

[video]https://www.youtube.com/edit?o=U&video_id=mBCLSxytkeM[/video]

part#2 direct link: https://www.youtube.com/edit?o=U&video_id=_N_m2g8jlho

[video]https://www.youtube.com/edit?o=U&video_id=_N_m2g8jlho[/video]

 

[Smitty192]

Thanks Elfster. Cheers to better health and a speedy recovery!

 

[elfster1234]

Thanks Elfster. Cheers to better health and a speedy recovery!

Thanks my friend

 

[LRRPF52]

I will add to this - a gas pressure curve for rifle barrel tapped gas has 3 critical aspects:

1. How long the bullet has been in the barrel before gas begins to flow into the operating system.
2. What the pressure of the gas is as it enters the operating system.
3. How long the dwell time is after the bullet has passed the gas port.

So it is true that a +2 gas system on a 22" barrel has similar dwell times to a 20" barrel with rifle gas, the +2 gas system will have a lower port pressure as well as more time between cartridge ignition and bolt opening. I would wager that a 22" or 24" +2 barrel is more reliable in every way than a 20 or 18" barrel with rifle gas.

Adjustable gas blocks can mitigate the pressure issue but not the other two.

I would add another consideration:

The volume of gas that flows through the port in a specified time, which has a lot to do with port location and port diameter, as well as plug dwell of the projectile passing the port to the muzzle.

+2" gas system makes a lot of sense in a 6.5 CM or .260 Rem, since we're pushing slower burning powders through a tighter bore, with tighter twist.

Hit the port with pressures of 20ksi, and it gets unruly with bad timing in the operating system.

 

[chevytruck_83]

Wasn't sure if it was best to start a new post or ask here. From what I'm reading a short barrel ar10 6.5 creedmoor will be problematic for all but the most competent gun smith's. So for someone like myself that's not a barrel like the proof research 24" camgas with a +2 gas tube would make it a whole lot easier to end up with a properly operating gun?

 

[The King]

Yes. Or the JP VMOS helps a LOT. I have the VMOS on my 20" proof research barreled JP lrp-07. The VMOS increases your deadblow mass in the buffering system from 2 elements to 5 elements.

With it my gun runs a 20" proof barrel with a suppressor and rifle gas with no issues. And it runs on the same gas setting suppressed or unsuppressed.

 

[chevytruck_83]

Just to follow up I purchased the jp barrel,bolt, adjustable gas block and operating system. It feeds 100% with everything I tried in it. The only thing I’m not crazy about is the carbon fiber lancer hand guard. It’s very lightweight and good looking but isn’t very solid. To as accurate as I could have hoped with 130 prime.

 

[R700LR]

Just to follow up I purchased the jp barrel,bolt, adjustable gas block and operating system. It feeds 100% with everything I tried in it. The only thing I’m not crazy about is the carbon fiber lancer hand guard. It’s very lightweight and good looking but isn’t very solid. To as accurate as I could have hoped with 130 prime.

Full weight bolt carrier or lmos? Did you get one of JP's SCS's? If so, H2 or standard version. I am considering swapping a 308 build to 6.5C

 

[chevytruck_83]

[No message]

 

[AZgeek]

Just to follow up I purchased the jp barrel,bolt, adjustable gas block and operating system. It feeds 100% with everything I tried in it. The only thing I’m not crazy about is the carbon fiber lancer hand guard. It’s very lightweight and good looking but isn’t very solid. To as accurate as I could have hoped with 130 prime.

Had related conversation with JP customer support ;last wek. They suggested a VMOS standard weight bolt carrier with the H2 SCS for a 6.5 Creedmoor.

 

[AZgeek]

Sorry. That last post was meant for R700LR

 

[R700LR]

Thank you, sir. BA SS 20" 6.5 Creedmoor barrels for under $190 shipped makes it tempting.

 

[AZgeek]

I hear ya. Unfortunately they use rifle length gas systems far as I can tell.

 

[HuntinBuddy80]

Ok guys so reading what you guys are saying, what can be done to mitigate the effects as much as possible? I've got a build with a 22" Black Hole Weaponry .260 barrel with rifle gas and an SLR adj gas block. I'm just breaking it in, maybe 50 rds on it so far and it is hammering but I'm getting more ejector swipe than normal, primers look fine and the rest of the brass is fine best I can tell. This is done off an Aero receiver set with an Aero HP BCG. Standard rifle buffer and spring. Is a JP SCS and heavier buffer going to help?

 

[gnatmm]

Same question here....I shoot a BA 18" 6.5 cm ( is a chopped 20") with rifle length. Flattened primers and battered brass are normal life. So before developing the right load I just decided to try to bring it as close to perfection as the bitch could possibly be so on the Christmas Eve I replaced the original aero non adjustable gs with a Sentry slr 8. Going Thursday to tune it.
Next Padom said either RCA or JP. So next will be replacing the entire Bcg with RCA ( is the easiest to get for me here in Europe) Full mass of course. In the meanwhile a JP SCS is already on its (long) way. An area 419 sidewinder will also join the team, will at least help in reducing felt recoil further. I'd love to hear from the Hide Sorcerers if something could be done to improve a situation which will be never close to perfection not until I will be able to have Craddock to deliver the right tube.
Using Peterson or Lapua brass is just hiding some dust under the carpet as it is reducing the load and shoot 2400ish pills wasting powder time and money.

 

[Birddog6424]

I will add to this - a gas pressure curve for rifle barrel tapped gas has 3 critical aspects:

1. How long the bullet has been in the barrel before gas begins to flow into the operating system.
2. What the pressure of the gas is as it enters the operating system.
3. How long the dwell time is after the bullet has passed the gas port.

So it is true that a +2 gas system on a 22" barrel has similar dwell times to a 20" barrel with rifle gas, the +2 gas system will have a lower port pressure as well as more time between cartridge ignition and bolt opening. I would wager that a 22" or 24" +2 barrel is more reliable in every way than a 20 or 18" barrel with rifle gas.

Adjustable gas blocks can mitigate the pressure issue but not the other two.

^^This..

You don't arbitrarily need a +2 on everything. I run a rifle length gas tube on a 22" barrel without hiccup. I know of a handful I have built with 20 and 22" barrels with rifle length gas systems that have zero issues. If I had a 24" barrel I would absolutely want a +2 length. Even the 22" wouldn't hurt. You don't need one for 18 and 20" barrels.

 

[AZgeek]

^^This..

You don't arbitrarily need a +2 on everything. I run a rifle length gas tube on a 22" barrel without hiccup. I know of a handful I have built with 20 and 22" barrels with rifle length gas systems that have zero issues. If I had a 24" barrel I would absolutely want a +2 length. Even the 22" wouldn't hurt. You don't need one for 18 and 20" barrels.

^^ I think this is a great general rule of thumb based on my research. That said, a rile+2 is mandatory for my 22" build. I consider rifle+2 an insurance policy well worth having assuming you are buying new.

 

[Birddog6424]

^^ I think this is a great general rule of thumb based on my research. That said, a rile+2 is mandatory for my 22" build. I consider rifle+2 an insurance policy well worth having assuming you are buying new.

I agree with you. My 22" barreled 6.5 pre-dates the +2 gas length availability. If I were to do it today I would put the +2 length on my rifle. My rifle length gas does run fine, but you make a good point that the +2 is added insurance of reliability.

Rifle length is still fine for 20 and 18" barrels. My 18" 308 SASS runs like a champ with rifle length gas. A little finicky with my can, though I think that's just because it gets so dirty so fast, and I'm not as Johnny-on-the-spot about cleaning it as I should be. But with a brake, she's reliable as the day is long.

 

[Big Moose]

the main key is the adjustable gas block more than anything.. i have a custom made from the ground up mega 6.5 AR with a 22" barrel with an extra 2" gas and IMO it makes for a super smooth shooting AR and is my crown jewel in my collection... with the custom brake = shoots damn near like a .223... i was in the middle of making a complete series on my MEGA 6.5 creedmoor when i found out about my whole cancer ordeal..... which i hope to pick up soon late spring

part#1 direct link:


part#2 direct link:

Nice build what gas block are you using?

 

[Cutthroatdave]

Good info here, I'm glad I looked here. I'm planning my next build and decided to use an AR 10 lower to build a 6.5 Creedmoor due to Ammunition availability. Sooo many variables that have to be considered.

 

[big_beau13]

Glad I stumbled into this thread!

I have a 6.5cm barrel being spun up at Compass Lake Engineering. Going with a 24" Bartlein 8 twist. I just followed up with them to see if I can have it cut for a +2" gas system based on this thread.

I will be running it with a TB Ultra 7 suppressor. Any recommendations on an adjustable .875" gas block?

 

[RyanScott]

My buddy has a 14.9” 6.5 with rifle length gas. It’s important to have a long gas system for this caliber.

 

[rpoL98]

6.5CM, factory ammo, 24" barrel, rifle gas, SLR adj GB, HP bolt, no suppressor. random handful of brass. FWIW.

 

[big_beau13]

Seems like there is some differences across the board, but everyone agrees that a longer gas system with an adjustable GB is the way to go for the 6.5cm, especially with a can.

 

[bobke]

Kickin this thread back to life for a moment. Having a 20” Krieger built with +2 gas and my question remains with +2 and gas port diameter. Shoot maybe 20% suppressed and will use Superlative 875 GB. What is the proper gas port diameter for this build? Smith suggests .102-.104, which seems a bit large, but gas can be regulated with GB. Or should this start smaller-say .095ish and work from there? Need to make a final decision before the cutting begins. Thanks.

 

[Earnhardt]

My buddy has a 14.9” 6.5 with rifle length gas. It’s important to have a long gas system for this caliber.

Does he use a can?

 

[NukeMMC]

Glad I stumbled into this thread!

I have a 6.5cm barrel being spun up at Compass Lake Engineering. Going with a 24" Bartlein 8 twist. I just followed up with them to see if I can have it cut for a +2" gas system based on this thread.

I will be running it with a TB Ultra 7 suppressor. Any recommendations on an adjustable .875" gas block?

SLR Sentry 8 or Superlative. I have used both and they both work well.

 

[RyanScott]

Does he use a can?

Mostly.