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Posted: 7/25/2017 10:09:28 PM EDT
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I just built a 300 blackout upper to throw on my sbr lower. I used a ballistic advantage 8 inch 300 blackout barrel like this one http://www.monmouthreloading.com/shop/ballistic-advantage-300-blackout-modern-series-8-drp-barrel/
It's a pistol length 300 blackout upper and I'm running subsonics suppressed with many cycling issues. I guess my first question is this, the gas port from what I have read on the ballistic advantage is around .099, my gas block is a geisselle and it says it's around .075, do I need a bigger gas block, or drill a bigger gas port in order to cycle subsonics? If i go with a bigger gas block like .093 will that make a difference in gas for cycling the bolt properly? I'm very confused at this point at whether the gas block itself will make a big difference in cycling or do I need to actually open up the gas port. Thanks for any help ahead of time. Essentially I would like this upper to run supers and subsonics equally and as effective and consistent as I would run anything else |
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That ".075" you're referencing is actually .750 and refers to the barrel/gas block seat diameter that particular block will work with. Same for the ".093", it's actually .930, or more commonly .936.
As for the actual gas port in the block, it's going to be double, if not more than that in comparison to the size of the gas port on your barrel. As long as your Geissele gas block is properly aligned with the barrel's gas port, I assure you it's not the issue. When it's comes to your issues, what exactly is happening? Will it lock the bolt back on an empty mag? |
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Ah, no it's not, a .750 hole is 3/4 inch. .930 is 15/16, bigger than your barrel, please stop giving people stupid advice. |
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Are you serious??? Did you not read the persons post you quoted? I'm about 99.99% sure he is correct in what he thinks the OP is talking about. I'm fairly certain the OP is referring to the actual size of the GB in regards to the .075/ .750 and the .093/ .936. |
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My issue's are that I am getting short stroking on occasion, and worst case scenario I am not even getting the bolt to cycle to pick up the next round. I have a carbine buffer and carbine spring for the record. |
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Both Donwe's original response and edited response show a clear lack of understanding of even the most basic parts of an AR (for starters, gas block manufacturers don't usually advertise their "port size" because they're pretty much all oversized in relation to the barrel's gas port to begin with) and the proper way to troubleshoot any associated issues. I'm thinking everyone's best course of action is just to ignore him. |
| Yes, it is correctly aligned and I haven't had a problem with the bolt carrier. I haven't tried different subsonics, I don't reload so they are mostly new manufactured. I will try different ammo but I would like an upper that eats all the subsonic ammo possible, that was the purpose of this build. If the gas block isn't the problem, would I need to possibly open up the gas port more? It's pistol length gas system, I have been told that should cycle most everything. |
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Yes, it is correctly aligned and I haven't had a problem with the bolt carrier. I haven't tried different subsonics, I don't reload so they are mostly new manufactured. I will try different ammo but I would like an upper that eats all the subsonic ammo possible, that was the purpose of this build. If the gas block isn't the problem, would I need to possibly open up the gas port more? It's pistol length gas system, I have been told that should cycle most everything. |
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Yes, it is correctly aligned and I haven't had a problem with the bolt carrier. I haven't tried different subsonics, I don't reload so they are mostly new manufactured. I will try different ammo but I would like an upper that eats all the subsonic ammo possible, that was the purpose of this build. If the gas block isn't the problem, would I need to possibly open up the gas port more? It's pistol length gas system, I have been told that should cycle most everything. Is there anyway you can measure your gas port as it sits right now? |
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