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Thread: Graphic Example of Twist Rate vs. Bullet Stability

  1. #1

    Default Graphic Example of Twist Rate vs. Bullet Stability

    I was shooting at BW range the other day, and I noticed the gorgeous wood on a rifle a few benches down from me. I complimented the owner on the rifle stock, and he said he had built it himself. The fit and finish, and the hand checkering was truly superb! The rifle was a Ruger model 77 in 6mm Remington, with the varmint weight barrel, and the barreled action looked as good as new.

    He mentioned that he was disappointed in the load that he tried that day, which was a Sierra 107 gr. hollow point boat tail match, and showed me a 100 yard target with two perfect silhouettes of that bullet. I am guessing that the rifle was the 1:12" twist that was originally supplied with all the early factory 6mm Remington cartridge rifles. That relatively slow twist was the cause of the cartridge's loss of favor compared with the .243 Winchester, which came with 1:10" twist, because the slower twist wouldn't stabilize the 100 grain 6mm hunting bullets of the day (much less the very long 107 grain Match).

    I took a picture of the group, because it was the best example I ever saw of an unstable bulllet result.

    Best Regards,
    JimClick image for larger version. 

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  2. #2
    Member 1Cor15:19's Avatar
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    Quote Originally Posted by midnightsunfun View Post
    I was shooting at BW range the other day, and I noticed the gorgeous wood on a rifle a few benches down from me. I complimented the owner on the rifle stock, and he said he had built it himself. The fit and finish, and the hand checkering was truly superb! The rifle was a Ruger model 77 in 6mm Remington, with the varmint weight barrel, and the barreled action looked as good as new.

    He mentioned that he was disappointed in the load that he tried that day, which was a Sierra 107 gr. hollow point boat tail match, and showed me a 100 yard target with two perfect silhouettes of that bullet. I am guessing that the rifle was the 1:12" twist that was originally supplied with all the early factory 6mm Remington cartridge rifles. That relatively slow twist was the cause of the cartridge's loss of favor compared with the .243 Winchester, which came with 1:10" twist, because the slower twist wouldn't stabilize the 100 grain 6mm hunting bullets of the day (much less the very long 107 grain Match).

    I took a picture of the group, because it was the best example I ever saw of an unstable bulllet result.

    Best Regards,
    Jim
    That is a perfect example of a key-holing bullet, due to instability. However, it's not because the 6mm Rem has a 1:12 twist. So far as I know all Ruger 6mm Rem rifles have been produced with the standard 1:9 twist. I know that my present 6mm is a 1:9 and I've owned/shot numerous others and all used the 1:9 as well. The 1:12 was standard for the 6mm's externally identical predecessor the .244 Remington. I'd have to check with Sierra, but I think they recommend a 1:7 (possibly a 1:8) twist for the 107 SMK. It's also possible that his loads were a bit on the mild side with regards to velocity. Higher velocity loads often provide improved stability when the twist is on the edge of effectiveness IME.
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    Supporting Member Amigo Will's Avatar
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    My old grease gun did that with 45acp at about 25yds.Don't think rifeling was much of a factor though
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    Member broncoformudv's Avatar
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    Quote Originally Posted by Amigo Will View Post
    My old grease gun did that with 45acp at about 25yds.Don't think rifeling was much of a factor though
    I have always heard the old grease guns chunked bullets downrange instead of spiraled them.

  5. #5

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    1Cor--That is good thinking on your part, and that may well be the case in his rifle. He was doing load development, and that was the smallest charge (starting) load of his loads. Maybe he gave up too soon. I didn't realize that it was only the .244 that had the slow twist barrels--some of the places I read about it didn't distinguish between them.
    Best Regards,
    Jim

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    It is because of twist rate. 105 and above BT target bullets require an 8" twist or less. The 1-12 will shoot the 105 semispitzer and lighter but the 107 is a very long target bullet and you have to use the faster twist. Berger bullets, in this cal and weight range, specify the twist needed to stabalize. You had it figured out the first time. J.

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    Quote Originally Posted by OldRgr View Post
    It is because of twist rate. 105 and above BT target bullets require an 8" twist or less. The 1-12 will shoot the 105 semispitzer and lighter but the 107 is a very long target bullet and you have to use the faster twist. Berger bullets, in this cal and weight range, specify the twist needed to stabalize. You had it figured out the first time. J.
    It sounds like too slow ofa twist to me.

    Velocity makes a diff, but not much, compared to twist.

    I had a 222 that wouldn't even get the heavier/longer/BT bullets on the target at 100 yards half the time.

    1-14" twist there, whatever. It didn't work. I had to go to 50 grain.

    That gun could have had other problems too, I spose.

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