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J.Boyette

Adjustable Gas block?

60 posts in this topic

Question?

how many of you use one? I found it to be a great help to my 16" DPMS LR-308

It reduced felt recoil down to almost a .223, very much like a 6.8SPC

Do you use one and if so how did you time your gas system?

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Maybe he has something here!  I was told by JP Enterprises the same thing about their bolt carrier assembly when I got it.  I already had a Larue gas block that is non adjustable and did not want to change it out.  They told me that if I used an adjustable gas block, you can turn down the gas blow back to only what is needed and it will reduce recoil to a minimum. I guess that is why they reduced the mass of the bolt carrier, so that not as much gas is needed to blow it back, therefore reducing recoil. I will get an adjustable and put it on and try it out and let you know the results for comparision. 

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What gas blocks are you running?

I hate coming to this site, it costs me a fortune  <laughs>

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Are you asking me?  I have the Larue extended on that would cover the area where a fixed site base would have been on a regular AR15.  I just had that one, so I used it.  I am going to go ahead and order a JP adjustable today.

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guys,

I run the JP gas blocks. BUT you can do one our self if you have the tools. If you do not have a drill press, and dies its to costly.

Check these out LINK I use the low profile under the handguards.

I got to go christmas shopping and will hit you guys back later.

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I think I will do that standard one. I can get it for $56.38 and shipping from Brownells

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I hate coming to this site, it costs me a fortune  <laughs>

It's kinda like we're all barging into your living room - when all the guys are around, nothing good happens...  <lmao> <dontknow>

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Guys,

The adjustable gas block I feel is a must have. Now you can make one your self. Just drill 90deg's to the gas port leading to the gas tube and tap that new hole and install a screw that will close off the gas flow

But I only do that to a gas block that I must have. I would just replace it with a JP.

Timing.


  • Load many mag's with just 1 rnd
  • Install gas block follow the instructions
  • Turn the screw until gas flow is cut off
  • Then go one full turn open and shoot 1 round
  • You should not be able to cycle the rifle
  • Keep going 1 full turn and shoot 1 round until you have brass ejection and bolt lock on the magazine.
  • Once done, turn the gas off 1/4 turn and shoot 1 round until you hit that spot the bolt fails to lock.
    The idea is to find that point the rifle kind of cycles. This is the sweet spot you want. Once found add a 1/2 turn and you are set.

Once you are done with finding the spot, I count the turns to take the screw out, add blue loc-tite and cound back down to install the screw.

The idea here is to get the cycle of the rifle to work on the least amount of gas needed. Once you find that spot and add 1/2 turn the rifle will cycle just fine.

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Once you are done with finding the spot, I count the turns to take the screw out, add blue loc-tite and cound back down to install the screw.

The idea here is to get the cycle of the rifle to work on the least amount of gas needed. Once you find that spot and add 1/2 turn the rifle will cycle just fine.

Cautionary note to people - this part will work if you already have your load developed and are stuck on that, or if you always shoot the exact same brand/load of factory ammo.  Blue Loc-Tite is easy to remove, but it's not necessarily easy when used on a small set screw.  And it's not gonna happen fast.

If you change handloads or factory ammo often, you might find that your rifle won't cycle like it should with certain loads.  My humble $0.02.

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98Z5V,

I have not experienced that, but their is alot I have not experienced :)

If some one wanted to go 1 full turn, not the 1/2 turn it would more then make up the diff between loads. I think the gas per load is the same volume no matter in most loads once the "adjusted open" position is found.

Have a great week.

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I think the gas per load is the same volume no matter in most loads once the "adjusted open" position is found.

I don't think I understand the "once adjusted open position" part of this, and how it equates to loads.  The amount of gas pressure will be dependent on the amount of powder, and that's all about the load of the round.  You can't tell me that a hot load for a certain heavy bullet will produce the same amount of gas pressure as a subsonic load for a light bullet, given the exact same gas system?  Am I confusing what you stated for "same volume" and trying to equate it to "gas pressure" here?

I can load a case hot, and it'll still make the "gas volume" requirement to cycle the action - with force - a hell of alot faster than a case loaded for subsonic.  The lightly loaded case might still make the same "gas volume" required to cycle the action, but it's not going to cycle as fast as the other one. 

If I cut down the pressure (gas port size, through an adjustable gas block) for a certain round, just to make it cycle with less force, it might not cycle a round that has a lesser powder charge.  Maybe it's not enough pressure to lock the bolt back on the lsat round, but everything else functions fine.  Maybe, it's not enough to throw the bolt back enough to strip the next round off the top of the magazine.  Not good at all.  Curious about this...

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This is a difficult question because there are plenty of variables, but here's the take from a negative-IQ perspective:

I think of the adjustment as an absolute restriction, basically a check valve that is only going to permit X amount of energy transfer. Whether I have determined this setting using a high-pressure round, or a low-pressure round, given either round only X energy will pass through, with any excess being passed elsewhere along the path of least resistance.

If you find this theory to be figurative swiss cheese, feel free to point out any/all flaws.  <thumbsup>

Evidence trumps theory, so lay the experience on me.

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You're right on, Matt.  You use the adjustment to restrict the gas flow.  You can't increase the gas flow, because it's only going to max out what the stock gas port will allow.  If you needed to increase gas flow, you would have to drill the gas port bigger, and go from there.

Different types of rounds are going to produce different gas pressure, though.  That's where I was originally going with my comments.  Sure, a 168gr from Winchester is going to be about the same as a 168gr from another manufacturer.  When you start seeing different powder charges for different weighted bullets, the pressures aren't going to be the same across the board.  Will a .308 semi cycle alal of them?  Yeah, most will cycle almost anything.  Some don't like certain types of ammo. 

Changing/asjusting the gas port flow with ana adjustable block isn't a bad thing.  You crank it down far enough, and it's not going to cycle everything out there, though.  I'm interested in the gas volume/gas pressure aspect here.

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guys,

as I understand it, its not a PSI thing its volume thing. As we know with any Ar system (15-10) the goal is to get the brass to eject at the 2 o'clock location. This shows a system that is timed. As you increase the volume of gas, the brass fly's to the 3 o'clock, then to the 4 o'clock and recoil and wear on parts in very high.

as you get to the 3:30 and 4 o'clock eject locations you will see after 30rnds some will stick and not eject, or rip off the base of the round.

So if I get a load, lets say 168 FGMM and time it to a 2 o'clock position, and then shoot 175 SMK FGMM the adjustment of the timing is very little. As a matter of fact I have found that 155grn, 168, 175's loaded to a normal level, the brass is with in 3" of each other in piles.

So that tells me the timing is good for two rounds, and great for one of them. This also tells me the volume of gas is not that different between the three.

now with timing, the main issue is dwell time also. This done by the gas port size, and the amount of barrel after the gas port to the crown of the barrel.

Case in point.

The dwell time on a 20" and 14.5" barrel is the same. 7" gas system and a 12" gas system. 8" this is why the two barrel systems where used back in the day, to keep the same dwell time between ammunition.

Now the amount of gas between the cartridge and the gas port is not the same. So this had to be adjusted by the gas port size. So what is a manufacture to do? drill the smallest hole for the widest amount of loads, this is also part of why heaver bullets shoot like crap is the wrong twist rate. The timing is off due to the slower bullet speed, hence less gas pressure.

Now one you get the smallest, hole drilled for a wide range of bullets and powder loads, this works but can be hell of the parts, as we all know. If you adjust from a full ON level to a manageable level that lets the bolt travel to the rear of the magazine, but not slap like hell on the buffer and compress the soft plastic stuff, you are saving parts and lowering felt recoil.

This is why I feel a adjustable gas system is needed on 308 AR rifles. try it, its only $50 and if it does not work, turn it all the way on and be done with it. But you will see a big diff in the performance of the rifle.

John

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i have 2 mini's and a Hakim with adjustable gas port.....good idea J.Boyette.....my LR only throws brass about 4 to 5ft at 3 clock no mater what i'm shootin' out of it......now my mini's before the AGB would throw about any load from 20 to 30ft!!!!

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So which one do you guys prefer? JP? PRI? Railed or low-pro?

Is the Noveske "switchblock" the same as an adjustable gas block?

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Robocop1051,

I have only used the JP so far many times.

but I would assume all brands work just fine.

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Bringing this thread back from the grave.

I was looking at a JP adjustable gas block today and I was wondering if the guys who are using it have experienced leaking around the adjustment nut? And how much blow by ?

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Isn't the JP made of aluminum? Maybe the threads in the aluminum block become oversize with repeated adjustment? Perhaps you ouls use some blus locktite to fill gap? Or could a helicoil be installed?

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Ok guys I am Beta testing a new adjustable gas block . Last week I put 120 rounds down range in my new 6.8 rifle. Well what i have to say is ; This works great and can be easily adjusted. Its a BMF !

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I have a switchblock on my 5.56. But on my AR10, which is a a SASS type build, I wanted a fuller range of adjustability and fine tuning. What I didn't want was loc tite and small screws. Originally I had planned to use the Armalite adjustable gas block. So I had my barrel turned for a gas journal of .875, not the typical .750.  Enter Syrac Ordnance. Leave your loc-tite at home boys.

http://www.syracordnance.com/collections/all/gas-blocks 

I'm waiting for them to unveil the .875 model, said to be in developement and ready for sale soon. (take a number and get in line)

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I can't reach the screw on my adjustable block with the troy MRF rails installed. ugh, that will be fun to tune.

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