Andy Posted July 10, 2020 Report Share Posted July 10, 2020 Alright finally "completed" my 1 year build (tax stamp) and took it to the range for its first 50-100 rounds of testing and was unable to get it to cycle subsonic rounds while suppressed (haven't done any unsuppressed shooting yet). I have an 18" barrel with rifle length gas system and a superlative arms .750 gas block. luther ar stock (with supplied 5.3oz buffer and spring). I've heard two theories: 1.) Impossible for rifle length gas system to cycle 308 supressed subs 2.) My gas block is faulty/installed incorrectly Sidebar I did shoot some cheap supersonic ammo through which cycled fine after 6 clicks from closed on previously mentioned gas block. Any thoughts or information needed? Thanks Quote Link to comment Share on other sites More sharing options...
98Z5V Posted July 10, 2020 Report Share Posted July 10, 2020 (edited) 1 hour ago, Andy said: I've heard two theories: 1.) Impossible for rifle length gas system to cycle 308 supressed subs BULLSHIIT. 2.) My gas block is faulty/installed incorrectly Probably Bullshiit. Sidebar I did shoot some cheap supersonic ammo through which cycled fine after 6 clicks from closed on previously mentioned gas block. Any thoughts or information needed? Your gas port diameter is too small to cycle subsonic .308 Win loads, with suppressor. What's your gas port diameter in the barrel?... Edited July 10, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
Andy Posted July 10, 2020 Author Report Share Posted July 10, 2020 Thanks for the input see attached for barrel specs Quote Link to comment Share on other sites More sharing options...
Radioactive Posted July 11, 2020 Report Share Posted July 11, 2020 Did you actually measure the gas port ? I’d measure it to make sure the spec sheet speaks the truth. When you ordered it did they know you wanted to shoot subsonic loads? Did you tell them you were going to run suppressed? Subs produce enough press to barely poop out the bullet. The typical supersonic port doesn’t allow enough gas to cycle the action with subsonic Loads. Suppressor helps by allowing what gas is there to remain a little longer but it still may not be a large enough pulse. Since it cycles with supersonic loads tells you that the mechanics are working. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted July 11, 2020 Report Share Posted July 11, 2020 (edited) 11 hours ago, Andy said: Thanks for the input see attached for barrel specs Hmmm... 0.089" gas port diameter, per specs, but as stated, did you measure that, and come up with that, to verify? At any rate, that doesn't matter, because... 20 hours ago, 98Z5V said: Your gas port diameter is too small to cycle subsonic .308 Win loads, with suppressor. What's your gas port diameter in the barrel?... How many times here on this board have I stated that the proper gas port diameter for an 18" rifle-gas .308 AR, .308 Win cartridge, with a 0.750"gas block journal needs to be... 0.093"~0.096"... Your gas port is too small. In fact, you may need an even larger gas port diameter to properly run subsonic .308 Win ammunition, even with a suppressor - in a gas gun... Something between 0.093"~0.096" is the bare minimum, though - so, even if it's what they say it is - it's too small... Edited July 11, 2020 by 98Z5V Quote Link to comment Share on other sites More sharing options...
DNP Posted July 11, 2020 Report Share Posted July 11, 2020 You already have an adjustable block. Go bigger with the gas port and you can always tune down if you have to. Quote Link to comment Share on other sites More sharing options...
mrmackc Posted July 11, 2020 Report Share Posted July 11, 2020 Yep, just don't drill all the way thru the barrel ! Run a nice round Amelican gimme wooden type writing pencil in the rifle bore at area of gassing port hole in bore start proper size drilling bit to be drilling, and then when you be seeing not some many wood chips S T O P drilling operations. (Mainly this is how the Chinese give directions) Quote Link to comment Share on other sites More sharing options...
Andy Posted July 13, 2020 Author Report Share Posted July 13, 2020 Okay thanks everyone, this is exactly what I needed and is good news. Was worried I was SOL with this build. May be a little while due to moving but once I get this completed I'll send an update with work completed and results incase others experience the same issue. Quote Link to comment Share on other sites More sharing options...
Andy Posted August 6, 2020 Author Report Share Posted August 6, 2020 On 7/10/2020 at 10:48 PM, 98Z5V said: Hmmm... 0.089" gas port diameter, per specs, but as stated, did you measure that, and come up with that, to verify? At any rate, that doesn't matter, because... How many times here on this board have I stated that the proper gas port diameter for an 18" rifle-gas .308 AR, .308 Win cartridge, with a 0.750"gas block journal needs to be... 0.093"~0.096"... Your gas port is too small. In fact, you may need an even larger gas port diameter to properly run subsonic .308 Win ammunition, even with a suppressor - in a gas gun... Something between 0.093"~0.096" is the bare minimum, though - so, even if it's what they say it is - it's too small... So finally got out to the range to test this out, drilled the gas port to 0.096 with a #41 drill bit and still no luck. The BCG does start to come back now a little but not nearly enough and gun got dirty pretty quick (guess that's expected tho with gas block opened up all the way). What would be best next steps from here, an even bigger gas port? Shorten/weaker buffer spring? Lighter BCG? Quote Link to comment Share on other sites More sharing options...
Radioactive Posted August 6, 2020 Report Share Posted August 6, 2020 Some others may be able to give you more specifics but my pistol length gas 375 socom uses a .101 gas port subsonic with a suppressor and a .116 gas port for subsonic unsupressed. subsonic rounds barely has enough gas press to poop out the bullet so the gas port has to be larger than normal supersonic size. Quote Link to comment Share on other sites More sharing options...
dpete Posted August 7, 2020 Report Share Posted August 7, 2020 Not sure if this helps but its another subsonic reference point. My pistol gas, 8" barrel supressed 300 Blackout has a gas port drilled to .108". 200-225 grain subs all run great but the BLK was designed to run subs or supers by changing loaded mags. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted August 7, 2020 Report Share Posted August 7, 2020 11 hours ago, Andy said: What would be best next steps from here, an even bigger gas port? Shorten/weaker buffer spring? Lighter BCG? That would be the absolute worst thing you could ever do. Running adjustable gas - even wide open - and you still need more gas for the subs. Open that thing up some more. Since 0.096" barely moved the BCG, open that thing up to 0.105" and see what happens. You may need to go up from there, too. Adjustable gas block can dial that back down when necessary. 0.125" is the absolute max that you can go, because that's the inside diameter of a gas tube. Try 0.105" and see what happens. Quote Link to comment Share on other sites More sharing options...
Andy Posted August 12, 2020 Author Report Share Posted August 12, 2020 On 8/6/2020 at 11:04 PM, 98Z5V said: That would be the absolute worst thing you could ever do. Running adjustable gas - even wide open - and you still need more gas for the subs. Open that thing up some more. Since 0.096" barely moved the BCG, open that thing up to 0.105" and see what happens. You may need to go up from there, too. Adjustable gas block can dial that back down when necessary. 0.125" is the absolute max that you can go, because that's the inside diameter of a gas tube. Try 0.105" and see what happens. Thank you everyone, I truly appreciate your patience and thoroughness. While new to the customization game I'm eager to learn, slowly building up that knowledge bank. I'll keep everyone updated once I get this done / tested. Quote Link to comment Share on other sites More sharing options...
Andy Posted November 29, 2020 Author Report Share Posted November 29, 2020 I know it's been a while, but finally got out to the range after my last modification (drilling gas port in barrel to 0.125") and still no luck, its not cycling and tbh not even close with the gas block all the way open. I think I'm just going to call it and either use supersonic rouhds or treat it as a bolt action subsonic gun. Quote Link to comment Share on other sites More sharing options...
98Z5V Posted November 30, 2020 Report Share Posted November 30, 2020 6 hours ago, Andy said: I know it's been a while, but finally got out to the range after my last modification (drilling gas port in barrel to 0.125") and still no luck, its not cycling and tbh not even close with the gas block all the way open. I think I'm just going to call it and either use supersonic rouhds or treat it as a bolt action subsonic gun. Lighten your buffer. It definitely appears to be a rifle buffer, on a rifle stock. There are 5 steel weights in an AR15 Rifle buffer, plus a spacer. There are 5 steel weights in a .308AR rifle buffer, no spacer. Remove one or two of the steel weights, replicate the length of those steel weights with a 1/2" diameter delrin spacer or two, and try that. No reason to stop now... Seriously... Not with the time you've put into this... Quote Link to comment Share on other sites More sharing options...
Andy Posted December 8, 2020 Author Report Share Posted December 8, 2020 On 11/30/2020 at 12:32 AM, 98Z5V said: Lighten your buffer. It definitely appears to be a rifle buffer, on a rifle stock. There are 5 steel weights in an AR15 Rifle buffer, plus a spacer. There are 5 steel weights in a .308AR rifle buffer, no spacer. Remove one or two of the steel weights, replicate the length of those steel weights with a 1/2" diameter delrin spacer or two, and try that. No reason to stop now... Seriously... Not with the time you've put into this... As always, thank you! You keep reminding me how much I have to learn ha-ha. Just pulled a few weights out and filled with spacers, going to a buddies farm this weekend to test out. Will let you know what the new results are. Quote Link to comment Share on other sites More sharing options...
COBrien Posted December 8, 2020 Report Share Posted December 8, 2020 I see you've made yourself some spacers, but if you decide you need/want some aluminum buffer weights, let me know. I've got 5 (I think...at least 3 for sure) sitting on my workbench getting in my way. 😆 Quote Link to comment Share on other sites More sharing options...
98Z5V Posted December 9, 2020 Report Share Posted December 9, 2020 10 hours ago, Andy said: As always, thank you! You keep reminding me how much I have to learn ha-ha. Just pulled a few weights out and filled with spacers, going to a buddies farm this weekend to test out. Will let you know what the new results are. This excites me... Quote Link to comment Share on other sites More sharing options...
billymagg Posted February 8, 2021 Report Share Posted February 8, 2021 On 7/11/2020 at 8:48 AM, mrmackc said: Yep, just don't drill all the way thru the barrel ! Run a nice round Amelican gimme wooden type writing pencil in the rifle bore at area of gassing port hole in bore start proper size drilling bit to be drilling, and then when you be seeing not some many wood chips S T O P drilling operations. (Mainly this is how the Chinese give directions) Dang, I just saw this,,, "area of the gassing port hole"! love it MrMackc... Quote Link to comment Share on other sites More sharing options...
BrianK Posted May 15, 2021 Report Share Posted May 15, 2021 I wonder how this turned out? I may have missed it, but do we know that the load he was using was actually capable of cycling the gun with a rifle length gas port? Quote Link to comment Share on other sites More sharing options...
Andy Posted December 8, 2022 Author Report Share Posted December 8, 2022 On 5/15/2021 at 12:06 PM, BrianK said: I wonder how this turned out? I may have missed it, but do we know that the load he was using was actually capable of cycling the gun with a rifle length gas port? Nothing I did could get it to cycle (store bought) subs, ended up removing all of the buffer weights even (filled with plastic spacers) and never even got the bolt to budge. So in total with gas port drilled to same diameter as gas tube and zero buffer weights and gas block fully open no progress. I retired the project and got a new toy for subs (300 BLK). Hopefully this helps some people who do a bit more research than I. Don't expect a rifle length gas system on a 308 to cycle subs. Only other known things I could have tried if I was still going for this would be getting a weaker buffer spring and using hand loaded ammo (well of course could get a shorter barrel and pistol length gas system). Figured at that point though shooting supers would be to over gassed than I was willing to mess with. With higher disposable income than when the project started just added another dedicated family member instead. Cheers and happy building/learning. Quote Link to comment Share on other sites More sharing options...
BrianK Posted December 8, 2022 Report Share Posted December 8, 2022 Thanks for the update. I didn't think you'd get it to work without trying magic. When I was loading subsonic .308 it was in a bolt gun. When I was loading subsonic .223 in an AR (Sierra 80s) I had the same issue you did with .308. I accepted that I was going to have a single shot AR with that ammo. There's just no way to keep port pressure high enough if it has rifle gas. Then I got a barrel in .223 and started to load 33gr subs that are hellyweird silent with a can. Subsonic in a semi takes something special. Re: 300BLK. Mine has pistol gas and even with that not all factory subs will function. OK, that might be too strong a wording. The 1st ones I tried, S&B 220s, wouldn't function. So I just wrote all of them off and decided to cast my own heavy bullets and reload for my gun. Now subs and supers work fine with no adjustment of anything on the gun. Of course the adjustments are all happening at the loading bench. FWIW, I was discussing 300BLK with a gent at the LGS just hours ago. I decided years ago that I REALLY(!) liked the cartridge. The gent mentioned how much he likes it without me even asking. On paper it's a dog compared to other cartridges but for what it does it's really good at it. It's the handgun I wished I had for years when I was able to hunt. Quote Link to comment Share on other sites More sharing options...
dpete Posted December 9, 2022 Report Share Posted December 9, 2022 Yep, for subsonic functioning in an AR, 300 BLK is the way to go. I just took my 4th deer with my 200 gr Maker handload. As the shooter I can't tell how quiet the gun is because of the action slamming back and forth next to my ear. 970-980 fps is the speed range mine likes with 3 different bullet weights. The Ruger American Ranch is my mousefart rifle with the same supressor, no action clanking around. Quote Link to comment Share on other sites More sharing options...
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