MarkLeupold Posted November 26 Report Share Posted November 26 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! Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 28 Report Share Posted November 28 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. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 28 Report Share Posted November 28 (edited) 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 November 28 by 98Z5V Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 28 Report Share Posted November 28 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... Quote Link to comment Share on other sites More sharing options...
MarkLeupold Posted Sunday at 05:04 PM Author Report Share Posted Sunday at 05:04 PM I'm not so set on the RLGS if a mid length gas would work better, that's just generally what the internet will tell you a 6.5 Creedmoor needs because port pressures are higher than 308... It's not wrong...I currently simulate the 6.5 Creedmoor about 30% higher port pressure for mid gas than the 308 does. Move the port out to a rifle length and the pressures are similar to my mid gas 308, if not a little lower for the Creedmoor. As for dwell time, the 308 has roughly .23 ms (0.00023 seconds) of dwell time whereas the rifle length system has about .1 ms (0.0001 seconds) of dwell time, just under half. Short dwell time has come more into vouge recently with barrels like 16" RLGS and even 14.6" RLGS from FOR Systems, albeit on 5.56 rifles. It supposedly has more overlap in the operating parameters when moving from suppressed to unsuppressed (especially with high back pressure cans), so it's gained quite a lot of attention for that. In my reading, the rifle needs enough gas volume to fill/accelerate the carrier, and if the port is the correct size, even short dwell barrels should function. That being said, I understand the large frame guns are a different beast and I am still learning. What makes the short dwell barrels tricky? I have a HuxWrx suppressor, so I don't usually account for it affecting rifle function an appreciable amount; lengthening the gas system in my case is more of an effort to create another soft shooting rifle that has balanced function and doesn't want to tear itself apart. I'm also not vehemently opposed to going to an 18" barrel, which is [barely] more common on 6.5 Creedmoor, but I grew fond of the 16" barrel with the suppressor in tree stands this deer season and it's a good thought experiment to keep my mind occupied for the winter months. Quote Link to comment Share on other sites More sharing options...
MarkLeupold Posted Tuesday at 04:51 AM Author Report Share Posted Tuesday at 04:51 AM A side note of interesting information that I found: Criterion puts a .086" port on their 16" RLGS 6.5CM Hybrid barrels. Of course, this is without any knowledge of what recoil system they'd be designing for, but it is another data point to have. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.