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Posted: 10/20/2015 12:36:55 PM EDT
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I have never used an adjustable gas block on an AR15 nor have ever shot an AR15 with an adjusted gas block.
I understand that it regulates the amount of gas fed back and thus affects the recoil and overall cycling. I assume getting less gas is probably quite nice on shorter barrels with shorter gas tubes. In a certain way, assume its also a surrogate for piston systems (which I not tried either). I am building an AR308 (Aero Precision/DPMS platform) for the first time with a 20" barrel. The next AR308 build will be an 18" with a mid length gas tube. I hesitate on a 16" barrel for a 308. Will I benefit from an adjustable gas block? If so how do I adjust it (turn the gas down until it doesn't cycle well and then turn it up?) Which blocks would you recommend? Any articles or reading recommendations are also welcome. Thanks for you help. |
| I went with an adjustable block from SLR for my 18" .308 build. Mostly for reliability, but I do want to run suppressed at some point as well. Most articles you read on the LR308/AR10 recommend an adjustable block. It really helps with not beating up your brass too. If you reload like I do, this is also a concern. |
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I went with SLR. Pretty sure you can't beat their customer service.
I went with an adjustable block because my gun came with an aluminum one which gave me pause, and I wanted to see if I could get my brass to last a bit longer. I actually got some good torn brass in some of my loads that by load data are safe but towards the upper end, and the lesser loads still were getting good stretch marks. Some super light loads that probably shouldn't have functioned the gun did fine, which all led me to believe it was overgassed in any case. Obviously a suppressor is going to generate more pressure, thus you can dial down the gas to compensate. I just cranked it all the way shut, gave it a couple clicks open, then fired and adjusted until I got consistent function/bolt hold open. Edit: by the way, the adjustable gas block seems to have reduced the stress on the brass. I've not done anything scientifical to confirm, but the brass does not seem to show the same indications of stress it did in the past. |
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Why adjustable gas blocks? Because you can regulate the gas pressures to coincide with ammo and shooting conditions. Being able to adjust the gas allows you to fine tune your rifle to your shooting techniques and ammo selection. Also, if shooting suppressed you can tone down the increased recoil impulse.
How? It's essentially a set screw that blocks the gas port. There's different designs that di the same thing, some better than others, but it's really a personal preference. To adjust, you simply shut the gas off completely, load one round in the mag at a time and fire them one by one adjusting after each shot until your bolt holds open. Then open another click or 2 for safe measure. They're not needed to get proper function by any means. Rather, they allow you to fine tune your gun. If going the adjustable route, it's ideal to use s lightweight buffer and lightened bcg if you can, but not necessary. But being able to fine tune, there's no need for all the extra mass. You gotta ask yourself have deep into this rifle and shooting are you going to get. Gonna develop your own loads? Want to compete with it? Suppressor or not? The adjustable gas block is not a needed expense, so i suggest figuring out if you'll use it for its intended purpose. If not, why bother? |
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I think the reason has been explain above.
I have the JP adjustable gas block (Clamp on), which in hind-sight is not the block that I want. This JP gas block does NOT shut off the gas totally, and it doesn't have a locking screw or other retention for the adjustment screw. The adjustment screw walks, so I have add another set screw to lock the adjustment. I would recommend gas block that has retention for the adjustment screw, some of the blocks has pre-sets with spring load detent that is really nice. |
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You don't really need an adjustable gas block on a 20" RLGS .308 Win.
The main reasons for an adjustable gas block are: * Reduce the mass of gas entering the Stoner Internal Gas Expansion system so that carrier velocity is reduced, bringing secondary reciprocating mass inertia to a minimum. This, combined with a muzzle brake, is preferred for competitive action shooters who want faster split times and ease of recovery when running shot-to-shot, and target-to-target. This is really where the adjustable gas block came from on the AR15, most recognizably from JP Enterprises. * Deal with an improperly ported gun, where the port is either too large, or too close to the chamber. This is more of a band-aid fix that will last for so long, because the port is choked, increasing port erosion. * Tame a suppressed gun, since the increased dwell time and accumulator behavior of a suppressor causes more gas volume in the same time to enter the carrier, which causes violent and early unlocking. If the rifle is ported correctly, with the window of ammunition you intend to shoot through it, you don't need the adjustable gas block. |
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Quoted:
You don't really need an adjustable gas block on a 20" RLGS .308 Win. The main reasons for an adjustable gas block are: * Reduce the mass of gas entering the Stoner Internal Gas Expansion system so that carrier velocity is reduced, bringing secondary reciprocating mass inertia to a minimum. This, combined with a muzzle brake, is preferred for competitive action shooters who want faster split times and ease of recovery when running shot-to-shot, and target-to-target. This is really where the adjustable gas block came from on the AR15, most recognizably from JP Enterprises. * Deal with an improperly ported gun, where the port is either too large, or too close to the chamber. This is more of a band-aid fix that will last for so long, because the port is choked, increasing port erosion. * Tame a suppressed gun, since the increased dwell time and accumulator behavior of a suppressor causes more gas volume in the same time to enter the carrier, which causes violent and early unlocking. If the rifle is ported correctly, with the window of ammunition you intend to shoot through it, you don't need the adjustable gas block. +1 If you're not going to use a suppressor or compete, you will not benefit from the adjustable gas block. You're already getting full mass operating parts, so you'll end up with the block mostly open. I suggest holding off on the adjustable block for now. I'd get a standard block, put some rounds down range and go from there. It would essentially be a waste of money at this point. However, it's your wallet. Empty how you see fit. If you get it now, you won't have to get it later. If your set on getting it now, keep it wide open until you determine your gun functions 100%. Then start tuning, first give yourself a baseline you can resort back to if you can't get it tuned right. |
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Quoted:
+1 If you're not going to use a suppressor or compete, you will not benefit from the adjustable gas block. You're already getting full mass operating parts, so you'll end up with the block mostly open. I suggest holding off on the adjustable block for now. I'd get a standard block, put some rounds down range and go from there. It would essentially be a waste of money at this point. However, it's your wallet. Empty how you see fit. If you get it now, you won't have to get it later. If your set on getting it now, keep it wide open until you demons your gun functions 100%. Then start tuning, bauxite give yourself a baseline you can resort back to if you can't get it tuned right. Quoted:
Quoted:
You don't really need an adjustable gas block on a 20" RLGS .308 Win. The main reasons for an adjustable gas block are: * Reduce the mass of gas entering the Stoner Internal Gas Expansion system so that carrier velocity is reduced, bringing secondary reciprocating mass inertia to a minimum. This, combined with a muzzle brake, is preferred for competitive action shooters who want faster split times and ease of recovery when running shot-to-shot, and target-to-target. This is really where the adjustable gas block came from on the AR15, most recognizably from JP Enterprises. * Deal with an improperly ported gun, where the port is either too large, or too close to the chamber. This is more of a band-aid fix that will last for so long, because the port is choked, increasing port erosion. * Tame a suppressed gun, since the increased dwell time and accumulator behavior of a suppressor causes more gas volume in the same time to enter the carrier, which causes violent and early unlocking. If the rifle is ported correctly, with the window of ammunition you intend to shoot through it, you don't need the adjustable gas block. +1 If you're not going to use a suppressor or compete, you will not benefit from the adjustable gas block. You're already getting full mass operating parts, so you'll end up with the block mostly open. I suggest holding off on the adjustable block for now. I'd get a standard block, put some rounds down range and go from there. It would essentially be a waste of money at this point. However, it's your wallet. Empty how you see fit. If you get it now, you won't have to get it later. If your set on getting it now, keep it wide open until you demons your gun functions 100%. Then start tuning, bauxite give yourself a baseline you can resort back to if you can't get it tuned right. It depends. I had an Armalite AR10T and it was terribly overgassed. I tried a heavier spring combined with a slash extra-heavy buffer, and it had so much gas impulse it actually felt worse. I put an SLR gas block on there and it felt perfect. Like you said - "if the rifle is ported correctly". That's a big "IF" and the purchaser has no control over that.... getting an adjustable gas block is always a safe bet. I'd argue ALL DI systems "can benefit" from an adjustable gas block, because it puts the power in your hands... do I want ultra reliable overgassing, or do I want fine tuned for the lowest recoil and smoothest unlocking possible? (not even discussing suppressed options) |
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