I have several AR-15's in 5.56 and I am looking to build a .300 AAC Blackout soon. I am just wondering when an adjustable gas block would be required? Is it only required for when you are considering shooting with a suppressor or for sub-sonic rounds? Can any one add input /clarify? I was looking to build a pistol .300 AAC with a 9 or so inch barrel then maybe also a full 16 inch carbine build. I might shoot subsonic ammo, but I do not plan on suppressing either at this point. Would an adjustable gas block serve any purpose for either of these two builds/configurations? When would you need one if the two configurations above were 5.56?
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wally
Member
IMHO never required, but can be helpful if shooting suppressed. To me you only need one if your barrel port is too large and normal loads are "over-gassed" (which to me means defective barrel). Might also be useful to hand-loaders shooting heavier than normal bullets.
Maybe .300 Blk is different, but if the port is sized correctly for its location in the barrel and the caliber, I think these things are generally a solution looking for a problem -- other than the situations I've already mentioned where you might need one.
Maybe .300 Blk is different, but if the port is sized correctly for its location in the barrel and the caliber, I think these things are generally a solution looking for a problem -- other than the situations I've already mentioned where you might need one.
I have a blackout. The only thing I did was switch to a standard weight buffer and it has worked just fine.
I did get an adjustable gas block for my .223. It's got a 10.5" barrel and it's suppressed. The empties were coming out at about 1:00 o'clock. The adjustable gas block fixed that.
Brad
I did get an adjustable gas block for my .223. It's got a 10.5" barrel and it's suppressed. The empties were coming out at about 1:00 o'clock. The adjustable gas block fixed that.
Brad
243winxb
Member
"Superformance in Gas Operated Firearms "by Hornady. Google,it.
adcoch1
Member
If you are shooting really light powder charges, or really heavy bullets, or suppressing the weapon, an adjustable gas block can help tune the gas pulse to the different variables. Very rarely necessary for functionality, but you can dial in where your brass lands by adjusting the gas block. I have built several 300 blk uppers, both pistols and carbines, and have yet to need an adjustable block.
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243winxb
Member
Overgassed AR ??
http://www.ar15.com/forums/t_6_42/466400__308_primers_blowing_out.html You would have to join, i think, to see photos. They show high pressure sign, with the primers falling out.
http://www.ar15.com/forums/t_6_42/466400__308_primers_blowing_out.html You would have to join, i think, to see photos. They show high pressure sign, with the primers falling out.
wally
Member
I'm not understanding how the adjustable block can help with really light loads as it can't make the gas port in the barrel larger -- unless you intensionally ordered a barrel with an oversize port. Maybe factory ARs that come with adjustable blocs are made this way? Are there any from non-boutique makers?
I did.
http://www.hornady.com/ammunition/superformance-in-gas-operated-firearms
Nothing really different, same situation as if you want to hand load heavier than normal bullets. If you want to buy this ammo with its special powder and abnormal pressure curve then you might want an adjustable gas block, but IMHO if you want a reliable autoloader stick with ammo it was designed to shoot or ammo designed to its "standards". If you want to shoot "anything" they still make bolt actions
There is a downside to adjustable gas blocks (like on the FAL) while it can be useful to have a gas cut-off (turns it into a "straight pull action") for suppressed shooting or launching things other than bullets, having a mis-adjusted gas system can leave you with a jam-o-matic.
243winxb
Member
Building an AR
Many different powders available, with a wide range of load data. Throw in all the different bullet weights. I would guess problems arise when parts are mismatched, upper vs lower. How many manufacturers of AR are there now? The headspace may be the only thing that is a standard. Put one together, see if it works, go from there, is my guess?? Example, just seen it. http://www.thehighroad.org/showthread.php?t=808801
Many different powders available, with a wide range of load data. Throw in all the different bullet weights. I would guess problems arise when parts are mismatched, upper vs lower. How many manufacturers of AR are there now? The headspace may be the only thing that is a standard. Put one together, see if it works, go from there, is my guess??
Example, just seen it. http://www.thehighroad.org/showthread.php?t=808801Arizona_Mike
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I like having the ability to tune my gas and to turn it off completely for even quieter suppressed shooting.
Mike
Mike
Shawn Dodson
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Many barrel manufacturers intentionally oversize the gas port to minimize problems with bcg cycling and to minimize the return of "defective" barrels.
Too much gas and the bcg cycles too quickly and too violently, increasing recoil and muzzle jump. There are to ways to remedy this: 1) install a heavier buffer to slow down the bcg, or 2) install an adjustable gas block to regulate the volume of gas ported to the bcg.
An adjustable gas block also reduces carbon fouling on the bcg and the bcg remains cooler.
Too much gas and the bcg cycles too quickly and too violently, increasing recoil and muzzle jump. There are to ways to remedy this: 1) install a heavier buffer to slow down the bcg, or 2) install an adjustable gas block to regulate the volume of gas ported to the bcg.
An adjustable gas block also reduces carbon fouling on the bcg and the bcg remains cooler.
Llama Bob
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In general adjustable gas blocks are used for suppressed rifles. In my experience most AR15 do not end up needing one - unless the rifle is extremely overgassed unsuppressed, it will be fine suppressed. However, on AR10s I've found them to be a good idea. It's easier to adjust a gas block than it is to change a buffer.
cougar1717
Member
Kind of surprised that JP Rifles hasn't been mentioned yet since they've been producing them for quite a while. When seconds matter in competition, after a compensator, the next step is an adjustable gas block that allows you to turn down the gas, so you can lighten the BCG and reduce the buffer weight to put shots on target faster.
Like the FAL, it helps to have similarly powered ammo. Having to tune the block for ammo that is too hot or too weak can be a pain.
Like the FAL, it helps to have similarly powered ammo. Having to tune the block for ammo that is too hot or too weak can be a pain.
The adjustable gas block is useful when the gas port is too large. Some will add a heavier buffer but it's better to tune the AR too run with the correct weight which, for an M4 style, is an H or H2.
It's also useful when a suppressor is used only part of the time.
It's necessary when running an AR too run with just enough gas with a particular lot of ammo, especially when using a lightened BCG in pursuit of the softest recoil possible.
Beyond that, there's little need for an adjustable gas block.
If a maladjusted gas block is causing reliability problems, adjust it. Simple enough to do
It's also useful when a suppressor is used only part of the time.
It's necessary when running an AR too run with just enough gas with a particular lot of ammo, especially when using a lightened BCG in pursuit of the softest recoil possible.
Beyond that, there's little need for an adjustable gas block.
If a maladjusted gas block is causing reliability problems, adjust it. Simple enough to do
grampajack
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Look into black hole weaponry. They have a gas system in between pistol and carbine for 300 BLK, and supposedly it doesn't require adjustable gas blocks or switching out buffers when going from suppressed to unsuppressed/super sonic vs. subsonic.
With that said, I always use adjustable gas blocks on my builds. They're not necessarily required, but I like being able to use the buffer/spring combo I want along with whatever ammo. That way I get maximum reliability across the board, as well as a softer recoil impulse in many cases. My choice is the Syrac line, but there are some relatively new ones that look nice as well.
With that said, I always use adjustable gas blocks on my builds. They're not necessarily required, but I like being able to use the buffer/spring combo I want along with whatever ammo. That way I get maximum reliability across the board, as well as a softer recoil impulse in many cases. My choice is the Syrac line, but there are some relatively new ones that look nice as well.
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