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Thread: SPR Inspired Build

  1. #11
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    Quote Originally Posted by Renegade04 View Post
    I did a build a couple years ago with an 18" LaRue Tactical Stealth barrel that I won. At 100 yards, I have managed to put three rounds touching each other using M193 ammo.
    Best I have done at 100 yds is a 1 1/8" group using Hornady 75gr OTM factory loads. GECO 55gr was around 2". Never tried M193 with it. Some of this is undoubtedly the skill of the shooter and I always shoot off a bipod or a range bag, so perhaps not the most stable rests to really find out the barrel's best accuracy.
    Last edited by nightchief; 12-25-17 at 19:43.

  2. #12
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    I usually shoot off a bipod and small rear bag, either at a bench or prone. I handload 99% of the time but ironically one of the best groups from my 16" BCM SS410 was 69gr Gold Medal Match at just a hair over .9" at 200 yards. With standard 55gr ammo, I'm lucky to shoot 1.25" at 100 yards with a 5 round group.
    Last edited by Vegas; 12-25-17 at 21:42.

  3. #13
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    Couple of 300 yard groups from today. Not too bad for using the QMS. In the bottom group, got that nice flyer there which I believe was the last shot of the magazine. I read somewhere recently that last round with the bolt locking back can cause flyers because of the change in pressure/harmonics of the bolt not returning to battery. I never really considered that before but seems feasible. Can anyone confirm or debunk that theory?




  4. #14
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    Quote Originally Posted by Vegas View Post
    I read somewhere recently that last round with the bolt locking back can cause flyers because of the change in pressure/harmonics of the bolt not returning to battery. I never really considered that before but seems feasible. Can anyone confirm or debunk that theory?
    Those seem like respectable groups. After building 16” and 14.5” middies, I feel like an 18” SPR-type build is in my future.

    As for bolt lock back, I’ve seen graphs with dwell times around or under 200 microseconds, which is the time that the bullet has passed the gas port but hasn’t left the muzzle. The gas starts acting on the bolt in this time interval. For the sake of theorizing, a cyclic rate of 800 rpm translates to 75 milliseconds, or 75,000 microseconds per complete bolt cycle. Basically, the bullet is long gone before the bolt ever gets to the locked back position. That’s my thinking, anyway.

  5. #15
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    If I can keep that going to 600, I'll be happy. I think there is room for improvement with the load and once I switch in a 2 stage, I'll probably see a small incremental improvement.

    Thanks for the insight on the bolt movement. Assuming those numbers are correct, probably no impact to accuracy. The other variable I didn't include was these groups were shot suppressed.

  6. #16
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    So switched from Varget to XBR to see how that works with the 77gr SMK. After a couple weeks of messing around, found a decent load that seems to work with a light crimp and 2750 -2790fps. The top are crimped with a Rem bench rest primer, the bottom two are no crimp with a cheapo Sellier & Bellot primer. The results with the S&B primer were pretty consistent at just over MOA. The Rem primer is consistently sub MOA.

    Bottom line, the barrel is shooter for sure with the right combo.




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