6.5 Creedmoor Gas Port Musings

[MarkLeupold]

The LR308 build I did about two years ago continues to run flawlessly and I am very satisfied with it...but that being said, it's probably time to put another in the safe. 

 

As always, gas port is the question. I emailed X-Caliber barrels and their sales team wasn't able to get me a number, but did say that I could request a port size on a barrel. I would really like to know what they would put on the barrel standard, but if I can't be sure, I'd like to spec out my own. The build would include:

• Barrel: 16" 6.5 Creedmoor
• Gas: Rifle length
• Gas Journal: .750" or .875" I haven't decided yet
• Buffer: H3 AR-15 (3-1/4" length, 5.4 oz)
• Buffer Tube: A5 (7-5/8" depth)
• Buffer Spring: Tubb's SR25 flat wire
• Carrier: JP Full Mass

So, my references based on research on this forum:

• An 18", 308 Win, RLG, .750" journal needs a ~.095" port [.001566 in³ volume, 5.5" dwell]
• A 20", 308 Win, RLG, .875" journal needs a .090" port [.001803 in³ volume, 7.5" dwell] 
• A 16", 308 Win, RLG, .750" journal "probably needs bigger than .094" (later found in a different thread that this would probably need to be maxed out at .125") [.002712 in³ maxed out, 3.5" dwell]
• The 16", 308 Win, RLG, .936" Fulton barrels needed a .105" port to run right [.002719 in³, 3.5" dwell]
• A 20", 6.5 Creedmoor, RLG, .936" journal "could use a...port diameter of .070" [.001293 in³, 7.5" dwell]
• An 18", 6.5 Creedmoor, RLG, .875" journal, .087" port was "too much gas" (Seekins AGB turned in 2.5 turns for good function) [.001816 in³, 5.5" dwell]
• A 20", 6.5 Creedmoor, RLG+2", likely .875" journal, .088" port after being modified by PROOF for function [.001858 in³, 5.5" dwell]
• A 20", 260 Rem, RLG, unknown journal, .071" port (probably getting opened up to .080-.090") [assuming .936" journal - .001330 in³, 7.5" dwell]

 

My supposition from this information is that I need roughly .002000 in³ of port volume. This equates to a .091" port on the .875" journal or a .102" port on a .750" journal. 

If anyone has any experience with a 16" rifle length gas 6.5 Creed/260 Rem, I'd love to hear about it!

[98Z5V]

That's an impressive amount of research that you did, just to make that post, and I commend you. 

I'll get my opinion in here either tomorrow or Friday, depending on the time I have.  I'll give you the exact port diameter that you'll need for either gas block journal size, man.  

I base all my 6.5 Creed suggestions from my two 20" Rifle Gas 0.750 journal .260 Rem guns.  Same bullet diameter, same exact gas needed.

Great job on your recoil system - that's exactly what you need.

[98Z5V]

Shiit starts getting tricky when you're messing around with 16" Rifle Gas - there's not alot of dwell time to play around with...

Here's a 22 ARC in that config...

12.5" Midlength Gas is the exact same rodeo - another 22 ARC with 0.750" journal...

Edited 23 hours ago by 98Z5V

[98Z5V]

I stick with 0.750" journals anytime I can, unless I MUST go up in journal size, just for a gas port that's needed.  Increase journal diameter, decrease gas port diameter. 

I'll get more into it later...