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Posted: 4/17/2026 6:26:21 PM EDT
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Do 6.5 Creedmoor builds need adjustable gas blocks? I'm piecing together a 20" rifle gas 6.5 Creedmoor rifle, which will be mainly shot suppressed but some unsuppressed usage as well. Does it need an adjustable gasblock as badly as my 308 builds did? Those we wildly overgassed regardless of what I tried to do with them, suppressed or not. A Riflespeed block cured those (way better than the Superlative Arms block did, and a lot easier to adjust too), but if I can put on your normal standard low profile gas block on a 6.5 and have it work reasonably well both with and without a can... It'll be built with a standard 308 BCG and a rifle receiver extension/buffer/stock; not a carbine setup. Basically I'm trying to see if I can save $150 or so bucks here 
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"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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I consider an AGB mandatory on any large-frame AR. The 6.5 I built had a Faxon 20" barrel and an SLR Sentry 7 block. I set it once and never touched it thereafter. My .308 build using similar components was more temperamental, but that just meant I had to adjust the gas once in awhile. My brother's .308 was even more finicky. So, based on those three points, perhaps .308 is more sensitive. We both sold our ARs to fund Robinson XCR-Ms (mine in 6.5, his in .308), which is way more pleasant to shoot suppressed. Buddy that bought those ARs loves 'em. |
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I already spent a bunch of money on a SCAR in 308, so I'm going "cheap" with a hand-rolled 6.5 using an Aero M5E1 upper/lower I've already built an AR pistol on I'm going to move that pistol barrel/gas block to an ACI / Andro Corp upper/lower I just fell into (after I SBR it - I already know the barrel and gas block work, so it should be pretty drop-in with it's BCG), put an actual stock on the Aero lower once I take the pistol barrel off, I found an M5E1 rifle length handguard for the upper so the 6.5 should go together nicely. By "cheap" I figure I'm into it for about a grand already (barrel, handguard, gas block, stock assembly), but it's still less than most factory offerings Then it's just glass. I wonder when Natchez will do another super sale on Burris... The only thing I'm wondering about is the barrel and upper; reading some other posts online, the Criterion barrel with the JP barrel extension might be a bit too long for the upper, so I might need some shims...but we'll see how that goes when it gets in. |
"Oh, bother," said Pooh, as he pulled the pin on another grenade...
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I have only used a standard gb on one (my first) LFAR it's chambered in .308 it didn't have any issue but it never had a suppressor on it in that config. Later I changed it over to agb. But, yeah it worked flawlessly unsuppressed. (16") Rifle gas, carbine extension. (that one has a criterion barrel, forget port size) add: I do have a 6.5cm but, I never mess with it. .308 meets my needs |
| I will agree that an AGB is pretty much required on a large frame. They can obviously work without it but the amount of pain and headache the AGB saves is more than worth the extra cost IMHO. I've found that once you move away from standard calibers normally found in a large frame they really just don't work with the AGB. I've done 308, 260, 6.5, 7mm08, 280 British and 375 Raptor so far and anymore I just roll the cost of the adjustable block into the build plan from the beginning. |
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Depending on the gas journal size/gas system length, you could also look into cutting off gas at the source to tame things. I’ve had great luck with the BRT gas tubes and am currently pinning together a 308 SBR mini MK11 that I fully expect will want some gas management. I plan to use the YHM suppressed block and will keep drilling it larger until I’m solid on reliability with and without a can. Only have experience with one 6.5 Creed gas gun and yes, it wanted/needed adjustable (reduced) gas. Not sure if it’s worse than 308 but same ballpark. |
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Originally Posted By Ohio_Man: Smaller bore but still big case capacity. You want a rifle+2” gas with an adjustable gas block for a 20-22” Rifle gas with an AGB for a 16-18” ESPECIALLY with a suppressor. I have an Aero M5 build, with 22" criterion rifle +2 and a syrac ordnance AGB (dating myself slightly there lol), shooting probably 80% suppressed and this is exactly the correct info. |
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Originally Posted By Scott_S: Try it with a standard gas block first. If it throws brass into the next Zip code then get an adjustable gas block. Yeah. I've only got one .308 AR. A GII. Worked just fine with the original gas block. Had the idea I might want a suppressor some day and bought a SA vented adjustable gas block for it and it works just fine with that one, too. It actually has less felt recoil to me than my AR15 .300 BO. Very pleasant to shoot. I just get lucky sometimes. |
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