High velocity "ftf" with my LR-308

NCHillbilly

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  • Jul 7, 2012
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    Went to the range today to work on some loads. Rifle is a DPMS LR-308, 24in, 1-10t. The loads were 178gr hornady A-Max, 42.8grs - 43.3grs varget, fc210m primers, LC 12 (1x).

    Anything that I shot that had a MV above 2600 fps resulted in a failure to feed. Also would not lock the bolt back after the last rd. If I shot below 2600 fps, everything worked properly. I even tried different mags, same result. Any ideas? I'd like to shoot the hotter rds if possible. Had good groups and no pressure signs. Sub- moa at 2620-2630.
     

    NCHillbilly

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    I do not have an agb on this rifle at the moment, but have considered adding one. I have a can sitting in jail, at the moment, that I intend to use on this rifle. I can maybe kill to birds with one stone by going ahead and changing that.
     

    NCHillbilly

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    Do any of you guys have a source for tuning parts for this weapon? Everything I see is for carbines. Mine is rifle length with an A2 fixed stock. I would prefer an adjustable buffer instead of having to buy numerous ones.

    I'll probably get a superlative arms gb. I've used these in the past on other rifles, and they've worked out well.
     
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    JS8588

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    357Max

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    Do any of you guys have a source for tuning parts for this weapon? Everything I see is for carbines. Mine is rifle length with an A2 fixed stock. I would prefer an adjustable buffer instead of having to buy numerous ones.

    I'll probably get a superlative arms gb. I've used these in the past on other rifles, and they've worked out well.
    Your issue sounds more like lack of gas to me. As you speed up velocity the powder burn is also getting more efficient. More complete burn, faster burn, + less dwell time for the gas since your bullet is leaving the barrel quicker @ higher vel.

    I'd start by lightening up your buffer. Swap a steel weight or 2 for aluminum spacers.

    Just knock the roll pin out of your buffer. You can cannibalize old buffers for weights.

    If you have access to a lathe you can make your own aluminum or steel spacers. The tungsten spacers are available.

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    Or just buy a kit with an assortment of buffer parts.

     

    NCHillbilly

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    What was strange was that my brass ejection was giving me mixed signals. I was shooting mostly 5-shot strings, and most of the brass was ejecting between 4:00 and 5:00 o'clock, with an occasional one or two landing around 2:00 o'clock.
     

    FatBoy

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    Is this reloaded brass? Are you small base sizing it if so?
     

    NCHillbilly

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    I am using once fired lake city brass. Although I have a small base size die, I've never needed to use it. Rounds chamber fine. This issue never popped up till I really started pushing my loads. My original long range load for this rifle was 178gr A-Max, 42.5grs IMR-4064, 1x lake city cases, and cci 34's. These rds would consistently put hits on 18in steel at 1100yds. I switched to VARGET and fgm210m primers to tighten up my groups and squeeze a little more mv out of it.
     

    FCS

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    Cases are starting to stick.

    Heavy up buffer and add an adjustable gas block.

    43.0 +/- couple tenths of Varget in LC brass w/178 is fairly warm load for as configured from DPMS, 24” bbl. Cases start sticking causing extraction issues, which uses extra energy and gun no longer running smoothly.

    Fixed up a fair number of DPMS, 24” rifles over the years. YMMV.
     
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    NCHillbilly

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    Thanks to all for the recommendations. I was kinda thinking along those lines, but have never had to tailor a rifle for the ammo. I guess I could back off the loads, but they shoot do damn good. Since I hope to have my muffler one of these days, I'll start with the agb.
     

    bfoosh006

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    Thanks to all for the recommendations. I was kinda thinking along those lines, but have never had to tailor a rifle for the ammo. I guess I could back off the loads, but they shoot do damn good. Since I hope to have my muffler one of these days, I'll start with the agb.
    I agree, wait until after the Adj. GB is installed... IMHO, those make a huge difference in the Large Frame AR world.
    After I installed my first one, the cycling was easier, the brass was less abused, it was easier to do follow up shots, and easier at the bench.

    A friends daughter fired it and commented , promptly, how soft shooting it was.
     

    Earnhardt

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    AGB first...
    if that doesn't work try a KAK 9.3 oz buffer or the HeavyBuffer 10 oz...
    And a Tubb's Flat Wire Spring...

    In all of my LR308s, when trying to push the velocities higher...the Adj gas block, Heavier buffer and the Tubb's Flatwire fixed everything...
    including the WSM's
     

    BCP

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    I would try an adjustable gas block, also if you aren't using a small base die that is a necessity too.
     
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    sinister

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    You're loading A-Maxes to magazine-length with compressed Varget loads in full-length sized Lake City brass.

    You're on the edge for function timing. Gas blocks and heavy buffers can only do so much before you start getting smoke around the primers (high pressure leaks) and pierced primer cups. Why the desire to win the velocity (vice precision) race with a self-loader? Adding a suppressor is going to change your time-pressure curve again.

    Check your bolt face for cratering.

    Assess where in the 8-step functioning cycle you're getting your hang-up: feed; chamber; lock; fire; unlock; extract; eject; and cock.

    First fix (no cost): drop your powder charge just a bit, or load the bullet out farther. You're seating a long bullet deep. 2640-2650 is routine in a 24-inch bolt-gun without a self-loader's internal magazine length limit.

    Second stab: try commercial brass, same powder charge. Maybe a bullet change.

    Third (fast-easy): an XH heavy buffer swap requires no professional or bubba gunsmithing.

    Gunsmithing fix on your next barrel: put the gas port out two inches and use a +2 gas tube.
     
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    FCS

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    Thanks to all for the recommendations. I was kinda thinking along those lines, but have never had to tailor a rifle for the ammo. I guess I could back off the loads, but they shoot do damn good. Since I hope to have my muffler one of these days, I'll start with the agb.
    Ironically, I've found it to be just the opposite if I want to shoot heavier bullets with maximum accuracy and as much velocity as possible from a gas gun. Gas gun system MUST be tuned or accuracy at distances is inconsistent, brass life suffers and reliability of function is questionable; I'm after as much of all three aforementioned traits as possible.

    50 fps with Varget isn't going to make up for a bad wind call over the known load that was shooting well at 1100 yards with 4064. I get it, done same thing myself (bit more speed is more better) but reality is the 50 fps won't make up for a bad wind call. IF that 50 fps costs you reliable functioning of your gas gun, is it really worth the cost?
    I'm a HUGE fan of Varget but will say that in 308 gas guns, 4064 is DANG hard to beat for the overall performance it offers.
    Yes, you can make Varget work well for your 24" DPMS, that is a known and many, MANY people have done so.

    If you have a higher back pressure can in NFA jail that you will be adding later to the DPMS 24"....the fun hasn't even started yet. You'll see appreciable difference between how rifle behaves with can on vs. can off.

    If getting one can to run on bolt gun and gas gun, I can see the appeal of going with TBAC, Mack Bros, Rugged, Dead Air, Silencerco or other higher back pressure cans as those cans do better at suppressing on bolt guns. LaRue TranQuilo may not suppress as well at muzzle but bang for buck has been the best gas gun suppressor I've used in terms of how long rifle will run w/o needing additional lubrication, cleaning and number of rounds fired before starting to see failure to function and not requiring adjustment of gas system to function when can is on vs. can is off.
    I've heard the OSS flow thru cans are right there also, I just don't have any first hand experience with the OSS products.
     

    BCP

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    Does it run well with factory match ammo? Because literally all factory match ammo you'll grab off a shelf will be over 2600 out of a 24.
     
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    BCP

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    To be honest, I'm a handloader. I've not bought factory ammo for any of my weapons in over 15 years.

    Well on the offchance you haven't figured it out yet a box of decent factory ammo would help eliminate the YOU factor. I ran all sorts of hot loads through my DPMS SASS without issue but that was after I got a small base die and polished the feed ramps. Prior to that it was a jam-o-matic.
     
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    NCHillbilly

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  • Jul 7, 2012
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    Well on the offchance you haven't figured it out yet a box of decent factory ammo would help eliminate the YOU factor. I ran all sorts of hot loads through my DPMS SASS without issue but that was after I got a small base die and polished the feed ramps. Prior to that it was a jam-o-matic.
    I haven't had a chance to mess with it since the original post, but was looking through my targets ( I mark them up and save them for reference), and noticed that I had been shooting 43.3grs of VARGET a few months ago, with no issue. It was a little cooler weather, and my velocity was down about 20 fps, but they grouped well with no feeding issues. I'm going to strip it and give it a good inspection and cleaning before changing anything.

    This rifle has operated flawlessly from day one, and I want to get back to that. even if it means backing off my loads a little. My issues popped up when I started pushing my ammo to the limit, so that, more than likely, is where I should start looking for a solution to my problem.
     
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