175s too hot for a gasser?

Iamero

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  • Feb 14, 2017
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    Hey guys, I probably could post this in reloading too but figured I would try here first.

    Setup:
    - DPMS factory slick side bull barrel 20" in 308
    - threaded 5/8x24
    - JP adjustable gas block
    - Elf match trigger
    - luth AR stock
    - huntertown arms direct thread 308 can



    I loaded up some 175 custom comps. Hodgdon showed 42.7gr as the max load for H4895 so I stepped back to 41.5 and did .3 increments up from. First load had very faint swipe marks, second load a little deeper, 3rd load blew a primer so I stopped.

    I threw in some factory 150 PMC and even that had faint swipe marks on the case head. Is this normal in a cheaper platform? Is it a result of the suppressor?

    Max load (42.7) showed like 2635 FPS so I didn't think it was going to be that hot.

    What velocites are you guys running? Anyone else loading 175s and H4895? Powder charges? Just curious before I do my next OCW. Should I start at minimum and work up? Hornady shows like 2400 FPS as max load.

    On the bright side the first two loads were both 3/4" easy.
     
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    hlee

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  • Jul 14, 2012
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    Faint swipe marks is pretty common on most 308 AR rifles, not just inexpensive rifles. I err on the side of the mildest load that gives the accuracy I'm looking for, without going over book max. I also compare maxes from several books to make sure one is not a statistical outlier...
     

    hamstur

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    If using 4895 in a gas gun, start at the low end and work up. It's been many years since I loaded for the M1A as an example but 41gr 4895 behind a 175gr in LC was a hot load. Start 39.5gr and work up.

    As everyone pointed out, Varget or RL15 is a better powder choice.
     

    Iamero

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    Good to know. I always thought H4895 and Varget were so similar in performance that I ended up shooting all 4895 because my 223 and 7.62x54R loads had both been worked up with 4895. Naturally I just sold my 8lbs of Varget to another hide member, hah.

    What are you guys getting for velocity on your 175s? This will strictly be a 500-800 yard gun so I don't need to rip them out. Just want steady performance out to that distance.
     

    padom

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  • Mar 13, 2013
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    Here is OCW and seating depth testing I did for a new 18" 1-10 Wilson 308 gasser a month ago. I put more time and effort into the 168 ELD-M though. They have a higher BC, are faster shooting and cheaper.


    175SMK Varget OCW Test


    YwtJST1.jpg



    175SMK Varget Seating Depth Test


    lu7DURu.jpg




    168 ELD-M Varget OCW


    fQy0gqZ.jpg




    168 ELD-M Varget Seating Depth Test



    qiI81B7.jpg
     

    Iamero

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    Dang that's pretty sweet Padom. I never messed with seating depth in gassers because I figured mag length was about the best you could get.

    I have 1000 175 CCs I bought off another member here for $220 so I got a crap ton of them for cheap so that's why I was shooting the 175s and not the 168 ELD.
     

    padom

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    Get yourself KAC or Larue mags and you won't be mag limited. They allow COAL of 2.875. PMAG suck, havent used them in years.
     
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    Iamero

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    Very nice, I'll have to check those out. I think my 4 mags are all factory DPMS steel mags. 2.810" OAL is what I have on those.
     

    mheimer_45

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    Didn't know that about the mags either. Now does anybody make one for a ar15 longer than 2.26?


    Sent from my iPhone using Tapatalk
     

    padom

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    Didn't know that about the mags either. Now does anybody make one for a ar15 longer than 2.26?


    Sent from my iPhone using Tapatalk

    Yep, ASC makes quality stainless steel AR15 mags that allow up to 2.316. Careful, they sell aluminum mags as well. You want the stainless steel mag.

    http://www.ammosc.com/223-stainless-...0-rd-magazine/


    They also make 308 stainless steel mags that allow 2.865" and are a lot cheaper than KAC or Larue. I have zero experience with them through

    http://www.ammosc.com/308-sr-25-20-rd-magazine/
     

    Iamero

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    Looks like I'll be ordering a couple of each.
     

    Fenix Mike

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    I run the LaRue mags and load is as follows in my 18 inch OBR
    175 TMK, Lapua brass, Federal GMM Primer, 44.6 gr Varget on a OAL of 2.845 (wont fit in standard mags, Larue or similar only)
    Im getting an average of 2600 FPS with sub 5 SDs on 5 shots, half MOA groups and boring at 1100 yards. My LWRC REPR 20 inch wasn't capable of the hotter loads like this without blowing primers, or destroying the brass, having feeding issues etc, but it still took 43.4 gr Varget and hit about 2575 fps using standard 2.800 and pmags with Hornady Amax 178s consistently.
     

    FCS

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    How heavy is buffer? I'd run at lease 6.5 oz, choke down gas until won't lock back on empty magazine after last round, then open until it will. Most suppressors add quite a bit of back pressure and is part of your issue.
     

    Iamero

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    That's what I wondered. I've never hand loaded for a gun running a suppressor before so I was sure how it would effect the pressure. It's just a factory buffer in there.
     

    NukeMMC

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    My 20" WOA 1:10" AR10B with an Ops Inc 3rd model suppressor shoots FGMM 168s at 2650 and 175s at 2670. I shoot 175SMKs with 41.7gr 4064 at 2.825" OAL in LC72Match brass and get 2670 fps. M118LR, depending on year/lot gets 2675-2700fps from the same rifle.

    I have been getting good swipes on all ammo from this rifle when suppressed, same with my GAP10 in 260 and the same can. The AR10 buffer ended up having an aluminum weight instead of all steel and the GAP has all steel weights. I am replacing the aluminum in the AR10 with a tungsten and same in the GAP with 1 of the steel weights. Probably end up needing a couple tungstens in each buffer. THat should slow down the unlocking of the bolt long enough to minimize the ejector marks. We'll see.
     

    Iamero

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    Good to know. Maybe messing with the buffer and going with a heavier weight would help a bit. You could tell on my loads that the swipes were getting worse the hotter I got on the load, but I think the blown primer was a result of a loose pocket.
     

    Iamero

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    Well did OCW starting a whole grain lower. Damn I couldn't be happier with the results! Will post pictures when I get home from the gym.

    Still getting bolt swipe swipe a little bit which I don't mind but it actually warps the case head it pulls so hard. I'm going to get a heavier JP buffer for it and see what happens.

    Many other advice always appreciated. I'm newer to the gas game.

    Top left: 40.6gr H4895 (going to chrono this and may just be my go to load)
    Bottom left: 40.9 H4895
    Right: 41.2 H4895 (I think I got excited on the last shot :( )

    Loaded to 2.790" with 175gr CC




     
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    bfoosh006

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    Sounds like the BCG needs to stay closed just a few milliseconds longer... try the KAK 9.3oz .308 rifle buffer and a Tubbs Flatwire .308 Spring.

    Those two things helped a lot with case swipe... ( along with the SLR adjustable gas block. ) You can see the Tubbs has added spring weight where you want it most.... with the BCG closed.

    The rifle runs 100% with the 9.3 and Tubbs.. with the SLR adjustable gas block set at 6 of 12 settings, middie 18"

    I think the "AR10" has plenty of volume of gas to run dang near any BCG and buffer / spring.... it just needs to extract a little slower.

    I even run the .308 Tubbs and a 7.5oz buffer in my blowback 9MM Colt pattern PCC... took the bark and blast right out if it.

    Here are some spring weight measurements from David Tubbs... just food for thought.

    A2 (old) - 7.6lb closed, 14.5lb open
    A2 (new) - 9.1lb closed, 16.7lb open
    Tubb Flatwire - 10.5lb closed, 16.3lb open
    Tubb .308 Flatwire - 13lb closed, 16.7lb open
    SpringCo White ? (standard) - 8.3lb closed, 16.3lb open
    SpringCo Red (extra) - 10.5lb closed, 18.4lb open
    SpringCo Orange (increased) - 13.9lb closed, 24.8lb open


    IMHO, an extra power spring isn't needed , nor wanted.

    I tried both the "Red" and "Orange" ... both caused needless muzzle dip, and were slamming the BCG really hard into the breach face