Adjustable Gas Block Question

Doc7 · Sep 22, 2017

Hello all,

I already know the drawbacks (which are the reason behind a thread like this) of having an adjustable gas block in this service, but it's what I currently have on a multipurpose rifle, and until I build or buy a new rifle, I am focusing on Light Mount, Light, Optic (aimpoint pro) that can go on this rifle as my HD rifle until I build one specifically for that service.

I have a JP Enterprise fixed A2 front sight style adjustable gas block on my 18" rifle length build with CTR Stock. I know people aren't 18" barrel fans in CQB/HD service but when I have the stock at position 1 (0 being closed) it is shorter than my youth stock Mossberg 500 w/ 18" barrel, and nobody would knock the maneuverability of that platform.

Knowing that this style which does not have a positive detent, instead relying upon an adjustment screw and a set screw, isn't it true that once I set it with an extra 1/2 turn past empty mag lock position, if I match mark the Adjustment Screw with a bit of high temp paint, I can easily see that it has or has not moved? Even if it was loosened to the point of "about to move" at the conclusion of my range session without me knowing it because the match marks still lined up at that point, it certainly wouldn't loosen to the point of failure in a 1-10 round encounter in an HD situation, is that correct? (that would mean it would have to move 1/2 turn closed in 10 shots)

Thanks for any input.

Klint Beastwood · Sep 22, 2017

Doc7 said:
Hello all,

I already know the drawbacks (which are the reason behind a thread like this) of having an adjustable gas block in this service, but it's what I currently have on a multipurpose rifle, and until I build or buy a new rifle, I am focusing on Light Mount, Light, Optic (aimpoint pro) that can go on this rifle as my HD rifle until I build one specifically for that service.
There's nothing wrong with having an adjustable gas block. They can be very useful. As far as home defense, that is very subjective, and ill just leave that alone.

I have a JP Enterprise fixed A2 front sight style adjustable gas block on my 18" rifle length build with CTR Stock. I know people aren't 18" barrel fans in CQB/HD service but when I have the stock at position 1 (0 being closed) it is shorter than my youth stock Mossberg 500 w/ 18" barrel, and nobody would knock the maneuverability of that platform.
JP is a very respectible company. As far as CQB goes, I wouldnt get to wrapped into barrel size anyways. The ability to manipulate your pivot point, knowing how to low port or high port if other people are in the room, how much you stay off walls is going and things like that will have to be tweaked but thats just how it goes. However I would probably avoid one man room entries. Pretty easy way to die. I would be more concern with slicing the pie nice and easy, working the depth and staying out of the fatal funnel, maybe addressing enemies through walls (but dont tell the liability patrol, because none of them been in a gun fight).
Short barrels in all honesty have their place like everything else, like working or infiltrating small spaces, or when conducting methods of entry working around tools and getting on your knees a lot when the weapon is slung. Vehicles. Etc.

Knowing that this style which does not have a positive detent, instead relying upon an adjustment screw and a set screw, isn't it true that once I set it with an extra 1/2 turn past empty mag lock position, if I match mark the Adjustment Screw with a bit of high temp paint, I can easily see that it has or has not moved? Even if it was loosened to the point of "about to move" at the conclusion of my range session without me knowing it because the match marks still lined up at that point, it certainly wouldn't loosen to the point of failure in a 1-10 round encounter in an HD situation, is that correct? (that would mean it would have to move 1/2 turn closed in 10 shots)
Probably a good idea to mark the set screw. I would be concerned however if it was moving that much, in general, but especially in a single range session.

Thanks for any input.

bfoosh006 · Sep 22, 2017

As long as continue to use the same ammo and do not allow your firearm to get dirty enough to slow the cyclic action... you should be GTG.

Personally, I would suggest going a full extra notch... you don't want a failure in a self defense weapon... ( don't split hairs ) you need the firearm to function 100% , for sure, every shot.

boom boom · Sep 22, 2017

Doc7 said:
Hello all,

I already know the drawbacks (which are the reason behind a thread like this) of having an adjustable gas block in this service, but it's what I currently have on a multipurpose rifle, and until I build or buy a new rifle, I am focusing on Light Mount, Light, Optic (aimpoint pro) that can go on this rifle as my HD rifle until I build one specifically for that service.

I have a JP Enterprise fixed A2 front sight style adjustable gas block on my 18" rifle length build with CTR Stock. I know people aren't 18" barrel fans in CQB/HD service but when I have the stock at position 1 (0 being closed) it is shorter than my youth stock Mossberg 500 w/ 18" barrel, and nobody would knock the maneuverability of that platform.

Knowing that this style which does not have a positive detent, instead relying upon an adjustment screw and a set screw, isn't it true that once I set it with an extra 1/2 turn past empty mag lock position, if I match mark the Adjustment Screw with a bit of high temp paint, I can easily see that it has or has not moved? Even if it was loosened to the point of "about to move" at the conclusion of my range session without me knowing it because the match marks still lined up at that point, it certainly wouldn't loosen to the point of failure in a 1-10 round encounter in an HD situation, is that correct? (that would mean it would have to move 1/2 turn closed in 10 shots)

Thanks for any input.

I think that you have answered your own question. I would just make sure that you have use a high visibility high temp paint and have clear observance of the screw's position. This can be difficult with some handguards depending on where your set screw is located and the handguard type the newer keymod and mlok types make it easier to observe the gas block than the railed types (if your adjustable gas block is under one) where you can tell at a glance if it is off. I do the same marking with the retaining screws on the gas block itself to make sure no movement occurs. If you do have a type that obscures what you need to observe, adapt it--drill an observation hole, etc.

Nothing wrong with an 18 inch barrel for s/d unless you plan on clearing rooms in houses or getting in or out of vehicles.

MachIVshooter · Sep 22, 2017

I didn't see in your post that you were actually having issues that would warrant fiddling with the gas system.

For all the ARs I've owned and built, I only had one that had gas system related function issues, a .308 AR that was overgassed with a suppressor, causing a bolt speed high enough that empties couldn't get out in time. I drilled & tapped the A2 FSB, made a stainless thumb screw to adjust, found the happy spot where it ran suppressed and unsuppressed, removed my stainless screw, installed a carbon steel set screw and TIG welded the thing.

bfoosh006 said:
Personally, I would suggest going a full extra notch... you don't want a failure in a self defense weapon... ( don't split hairs ) you need the firearm to function 100% , for sure, every shot.

See above. Overgassing can cause the bolt to outrun ejection or mag feeding. How much one may want to increase the gas flow via turns of the screw after getting bolt hold open depends entirely on the barrel port size and pintle (screw) size.

Varminterror · Sep 22, 2017

I think guys who worry about AGB's adjustment screws coming loose must not shoot very much. After shooting AGB's almost exclusively for ~20yrs, with and without lock screws, with and without detents, my experience would say a screw type is more prone to lock up than it is to EVER shoot loose if you have more than a few hundred rounds through your AR. Carbon build up or gas torching will make that screw hang, for some of my rifles, I'll even pull my set screw to clean (and chase it if needed) every so many cleanings just to keep it from locking up on me.

Way back, AGB's weren't available like they are now, so I was drilling and tapping standard blocks to convert them to AGB's, almost all of those I just did a single set screw with high temp thread locker. Wanna change it? Rattle trap 5-10 rounds to get it hot and change it. Easy.

I wouldn't use high temp paint, but it would work. I use a chisel and make witness marks on my AGB's. I make 1/8 turn marks on some of them, with ONE witness mark on the screw, and then when I find my setting, I lengthen that mark ever so slightly (a guy could paint fill it). This is just one of those "brain itch reliever" things, not at all necessary, but before a match, I can look at the marks and know nothing has moved. Nothing ever has, but it's on my pre-match checklist all the same.

I only open a half turn past lock back, and have never had any reliability issues with the AR's I've built or rebuilt (a few hundred). Going a full turn with most models isn't likely to induce an overgas condition, but it's also not necessary.

Doc7 · Sep 22, 2017

Thanks

I can easily see my screw.

boom boom · Sep 22, 2017

Varminterror said:
I wouldn't use high temp paint, but it would work. I use a chisel and make witness marks on my AGB's. I make 1/8 turn marks on some of them, with ONE witness mark on the screw, and then when I find my setting, I lengthen that mark ever so slightly (a guy could paint fill it). This is just one of those "brain itch reliever" things, not at all necessary, but before a match, I can look at the marks and know nothing has moved. Nothing ever has, but it's on my pre-match checklist all the same. .

Your marking is more elegant and permanent and I use that for timing barrels and the like where permanence is desired, but one reason for using paint is that it is easier to remove and can be more visible (both good and bad) under some handguards. Same reason liquid paper or nail polish can be useful on sights from time to time--they indicate the mark without permanently altering the firearm.

FL-NC · Sep 22, 2017

At the moment I guess you need to run what you have- but for a HD gun, I would just buy one of those $400-$500 S&W, Ruger, PSA or the like, add irons and a light, and consider it done.

Adjustable Gas Block Question

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