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Thread: New 6.5 Grendel build feed issues

  1. #1
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    New 6.5 Grendel build feed issues

    Guys-

    Have a new build that I am having issues with.

    Here is the hardware:
    Rainier arms upper/lower
    Odin 20" barrel
    Precision Firearms BCG
    Magpul furniture
    Vortex scope

    I am currently shooting Hornady 123 grain SST box ammo, and about the 7th or 8th round, it will jam. I tried a 6.5 Grendel 10-round mag from Odin, and a 15 round 6.8 mag, and it did it with both. I have shot it with and without my supressor, and that didn't change anything. My buddy and I tried a regular buffer, and a H2. Our thought behind trying the heavier buffer was to slow the cycling of the bolt down a smidge, but it still does it. Any suggestions from the brain trust? Pics attached. Any suggestions are welcome, thank you.
    Attached Images Attached Images

  2. #2
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    Bolt looks pretty dry, is it ? Try with more lube with the H2.
    Try some other mags...

  3. #3
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    Do the basics, check for matching feed ramps (m4 or not).

    Swap with some known good mags. Never heard of the Odin mags, they may be ok, but to me you have not fault isolated out the mag yet.

    My and buds grendels have never been picky with mags, Cproducts, AA early mags, and my new fav, AA elanders all work well.

    But the fact younare using a 10 round mag stands out to me. I would get on the Grendel forum and find someone in your area who will loan you a known good Grendel mag.

    Also, is the bolt locking back reliably on the last shot? Are you using an adjustable gas block? (Could be set too low)

    It's hard to tell from the pictures, you need to determine if it's short stroking or just jamming FTF. Is the bolt behind the cartridge head?

  4. #4
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    Thanks for the comments, guys. I tried shooting it on Saturday, and it did the same thing. Took the bolt out and added some oil, and that didn't change the result. Thank you for mentioning the gas block; the one currently installed is non-adjustable.

  5. #5
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    Quote Originally Posted by WUnderwood View Post
    Thanks for the comments, guys. I tried shooting it on Saturday, and it did the same thing. Took the bolt out and added some oil, and that didn't change the result. Thank you for mentioning the gas block; the one currently installed is non-adjustable.
    It should be ok then, assuming a quality barrel mfg.

    The fact that it's working right for the first few rounds really make me think you're dealing with something magazine related. Personally, I'd go ahead and get an order in for some AA elander mags.

    If you don't, I would certainly try to borrow some known good mags.

    One quick question, as the follower and your magazine marked for 6.5 Grendel? It is a different follower, and the last rounds in the magazine, the more the follower can have an effect on feed angle

  6. #6
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    The gun is not short-stroking, and locks open after the last shot. I will try a different mag, and see if that helps the issue. Much appreciated for the suggestions.

  7. #7
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    Your malfunction is called a Bolt Over Base Failure To Feed.

    It is usually caused by 2 main problem sources:

    Cyclic rate out of timing
    Weak magazine spring

    Cyclic rate is driven by the gas system, then tamed with carrier and buffer weights and spring strength, as well as adjustable gas. You normally don't need adjustable gas on a 20" RLGS unsuppressed.

    If the cyclic rate is too high, the buffer and carrier will rebound pretty hard, then return to battery so fast that the magazine spring doesn't have time to lift the cartridge stack into presentation for proper feeding, and the carrier face will feed the cartridge instead, causing the bolt lugs to dig into the case wall as seen in your photos.

    If there is insufficient gas to cycle the action (not enough to lock back on the bolt face), then this can happen too, where the carrier will short-stroke, pick up the cartridge and feed it forward, causing the bolt lugs to dig into the case wall.

    What buffer type, RET (Receiver Extension Tube), and spring are you using?

    What gas block are you using and how did it fit? (Loose, tight, I needed a hammer and brass dowel to get it to press-fit, etc.)

    How did you align the gas block to the gas port on the barrel?

  8. #8
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    Thanks for the response, LRRPF52.

    I am using a H2 buffer, commercial extension tube, and I am not completely sure on the spring, but I am guessing a standard carbine spring.

    Also, I ordered a Geissele Super 42 Braided Wire Buffer Spring and Buffer Combo today, and my buddy has an adjustable gas block that we are going to try out. I also ordered a E-Lander 10 round magazine, that hopefully will narrow down my issues/problems.

    What mags do you use in your 6.5 builds?

  9. #9
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    I like the Elander 17rd mags the best.

    They are coated with a very smooth finish that has very low friction, and the white follower is very slick inside the body.

    How is your gas block installed, and what did you do to ensure the port was aligned?

    Did you happen to measure your gas port diameter on that barrel?

    Is your bolt locking back with the bolt face caught on the bolt catch, or is the catch arresting the face of the carrier?

  10. #10
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    Op, can you post some pictures of the bolt face with the BCG removed and some of the stoppage showing the bolt face?

    These large rim variants can get hung up on the ejector while feeding from one side of the magazine.
    Black River Tactical
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 11.5" CQB, 9" PDW
    BRT OPTIMUM-S Barrel - 11.5" CQB Suppressor Gas Drive
    BRT OPTIMUM-S Barrel - 11.5" SB Suppressor, 11.5" SBT 25 Deg Tapered Shoulder Suppressor
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT EZTUNE Gas Tubes - CAR and MID
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

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