Range Report JP Adjustable Gas Block and load testing

J.Boyette

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  • Nov 13, 2003
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    rifle: 16" LR-308
    Gas system: Carbine Length gas tube
    Gas Block: JP Adjustable low profile
    Handguard: JP Rifles

    Idea.

    To fully close off the gas system, do load testing with Nosler 155 Competition bullets

    Once the accuracy load is found as a single shot dial on the gas to get bolt lock back on 20 single loaded mags. Once at this point count out the turns until enough thread is shown to add blue loc-tite

    How does this sound?

    John
     

    wnroscoe

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    Re: JP Adjustable Gas Block and load testing

    Thats going to change the tune of your load. My guess is the groups will open when you open the gas block.

    I'd adjust the gas block to just let the bolt lock back while single feeding your test ammo. Load several mid range loads to establish the gas setting and start your test. Fine tune the gas block after the load is established and you'll be GTG.
     

    J.Boyette

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    Re: JP Adjustable Gas Block and load testing

    Thats what I do not know, I would ASSUME that a non-over pressured load would shoot the same in a single shot or semi mode. Like factory match .223 in a bolt / Ar-15 rifles.

    But I do not know.

    I ASSUME as a single shot, I would get the same level of accuracy as a 16" bolt action shooting the same load. I wish I had a 1/10 twist 16" 700 to do a side by side test.

    "thats an idea"

    Then see how the cycling of the action makes a difference.

    Oh one point.

    A2 stock with a A2 full size buffer, no extra weight in the BCG.

    John
     

    Goin'Hot

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    Nov 14, 2008
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    Re: JP Adjustable Gas Block and load testing

    You can go ahead and add the blue loctite. It won't lock the screw. Open the set screw 1.25 to 1.5 turns and test your loads. Once you get the load, tune the gas.
     

    J.Boyette

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  • Nov 13, 2003
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    Re: JP Adjustable Gas Block and load testing

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Goin'Hot</div><div class="ubbcode-body">You can go ahead and add the blue loctite. It won't lock the screw. Open the set screw 1.25 to 1.5 turns and test your loads. Once you get the load, tune the gas. </div></div>

    I assume you have done this before? So my question still stands. Did you ever test the rifle as a single shot first to find the best load?

    Thanks
    John
     

    Rafael

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    Feb 26, 2003
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    Re: JP Adjustable Gas Block and load testing

    John;
    I have never tried this before. It sounds like an interesting experiment.

    Still, I would want to find a load that works well with the weapon in normal shooting condition.
    If it shoots the same in both conditions, then there is no point in load tuning in that condition. If it does not.....I don't see the point of tuning a load to a weapon condition that will not exist in the future.

    Another question for you, while you are tweaking.......
    Does the gas block adjustment change anything?
    Is this one more variable to tune...for more than just reliable cycling?

    Excuse the rambling.
    laugh.gif
     

    J.Boyette

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  • Nov 13, 2003
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    Re: JP Adjustable Gas Block and load testing

    Rafael,

    Thats the question per-say.

    I would think that a load that shoots lights out would work in semi and single shot the same way right?

    What honestly is the diff in single shot and semi if the bolt is locked and the bolt opens with the correct dwell time? This is why I want a adjustable gas block. To get this as close as I can.

    The main accuracy issues I see is disturbing the natural point of aim wile ejecting the spent case with too much dwell time.

    Feeding recoil, or the movement of the bolt will happen after the bullet left the barrel. So the natural point of aim is not affected.

    The other options is moving the gas port to a mid-lenght or extending the gas tube with a pig tail, or all three. shorter dwell time, adjusting gas volume, lengthening the gas tube to adjust the timing of the bolt, and all adjustments in between.

    I sent a e-mail to huskey, I will have the right way to skin this cat on Monday. but it fun to think right now.

    One option is to add weight to the bolt carrier to slow it down, or adjust the buffer weight or spring to a lighter / heaver spring.

    So just thoughts to see whats right about this. With a dwell of 9" with a .308 its going to be fun to get this right.

    but he question of a single shot to get the right load is a function of equipment testing. I THINK this would pick the best load the barrel likes.

    Then try to time the system to run on that load.

    Thoughts?

    John
     

    mattmcg

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    Re: JP Adjustable Gas Block and load testing

    J.Boyette,

    I've load developed for two LR308 rifles with JP adjustable gas blocks and didn't find much difference (+/- 20fps) in chrono speed with the gas block turned off vs gas block allowing BCG to lock back on empty mag. I think your method will work to optimize to your barrel harmonics on the load.

    The bullet looks to be well out of the barrel by the time the BCG has gone out of battery if the gas block is properly adjusted.

    Your methods seem sound to me given my experience with a similar platform.
     

    mattmcg

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    Re: JP Adjustable Gas Block and load testing

    Also of note, I have built 3 LR308s. I started out on the first one with a fixed Badger MK gas block but the 24" barrel allowed too much pressure to travel to the BCG causing a rather violent reciprocating force. After adding super-heavy buffers, it became very apparent that the gas blocks needed to be adjustable until manufacturer's settled on gas hole specs to account for differences in barrel length. The industry still seems a bit shy of knowledge in this area to date although LMT's new 308 platform seems to have cracked the code.

    After my first build, I used JP adjustable gas blocks on the next one and found that it solved my earlier problem. So you're on the right track here as well.
     

    J.Boyette

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  • Nov 13, 2003
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    Re: JP Adjustable Gas Block and load testing

    As always,

    Huskey informed me where I am wrong and right with his experience.

    So off to the build room I go once the parts come in.

    John
     

    Rafael

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    Re: JP Adjustable Gas Block and load testing

    Thanks for sharing those thoughts, John. Lots of questions and I am curious to the answers as well.

    You are hitting me with new info all around as I did not even know one could add weight to the carrier. Excuse my ignorance here. My Rock River is far from a spectacular shooter and I think your experiment may be of use to me.

    I am interested in what you find out....and have been reading what everyone else said here.
    I will be paying attention!
     

    J.Boyette

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  • Nov 13, 2003
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    Re: JP Adjustable Gas Block and load testing

    Check your e-mail listed in your profile.

    REAL data just went your way.

    John
     

    esorensen

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    Re: JP Adjustable Gas Block and load testing

    I have modified my AR10T 24" that came from Armalite with a huge gas port. When I first got the rifle, I developed some very great loads for it. I then got The TUBB CWS and TUBB Spring for it. No difference in accuracy really. Just a lot slower recoil impulse. I then added a screw into the existing gas block to help eliminate some of the gas getting to the carrier. This has worked out well. The original hand loads I developed still shoot well. It is my opinion, that the bullet is long gone from the barrel before the bolt even begins to unlock and come out of battery. If the hand load recipe is solid, what has been done to change the gas has no real effect. The only change I have noticed is the brass lasts longer and lands in a neater closer pile.
     

    Powder_Burns

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    Re: JP Adjustable Gas Block and load testing

    I shot factory ammo and tuned the gas block so it would lock the carrier back, then started load development with those settings. If the load I decided to use felt a little overgassed, could try shutting the gas off in 1/8 or 1/4 turn increments to fine tune it..
     

    338LM

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    Re: JP Adjustable Gas Block and load testing

    I have done a lot of load development and long range match shooting with my GAP .308 AR10 out to 800 yards. Groups do not open up on my rifle no matter if the gas is turned off or no matter what the gas setting is. Rifle also shoots the same tight groups whether it is single fed or autofed. Thats my experience with my rifle and a JP adjustable gas block.