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Advice on twist rate for 6mm BR barrel

CCCCCCCC Member Posts: 10 ✭✭
edited January 2009 in Perry Shooter Competition Shooting and Reloading Forum
Hello - talking 6mm BR rifle here and seeking opinions.

Am ordering a barrel and have just about decided on a 1 in 9 twist as seemingly best, in that I am planning mostly to use heavier bullets, and occasionaly mid-weight, but rarely, if ever, the lighter variety. What do the experts think of this choice of teist rate?

Also am thinking of a chrome-alloy Douglas air guage barrel. Seems like a good compromise with decent quality but not "big name" cost. Any thouhts?

CCCC
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Comments

  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    CCCC,

    Determining twist rate is based on the length of the bullet.

    As usual, the twist rate will depend on what you intend to use this cartridge for. If it's for long range target shooting, you'll want a 1:8" twist. If it's just for standard bullets for hunting and plinking, the 1:9" might be sufficient.

    From Shilen:

    6mm/.243

    - 8" Special for VLD bullets over 100 gr.
    - 8"* Ratchet rifled 4 groove
    - 10" For bullets up to 120 gr. and VLD under 100 gr.
    - 12" for bullets up to 85gr.
    - 13"* for bullets up to 75gr.
    - 14"* for bullets up to 70gr.
    - 14"* Ratchet rifled 4 groove
    - 15"* Special for bullets up to 70gr.

    Best.
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  • Hawk CarseHawk Carse Member Posts: 4,381 ✭✭✭
    edited November -1
    A long range or Long Range shooter will want an 8 twist for 105 grain bullets. A benchrest shooter will use a 14 twist for 68 grain bullets. I think the ones in between are neither fish nor fowl unless you particularly wanted to shoot, say, an 87 grain varmint bullet. Which you say not.
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  • CCCCCCCC Member Posts: 10 ✭✭
    edited November -1
    Thanks to nononsense and Hawk Carse. I headed for the 1 in 9" twist after quite a bit of research in writings of those who shoot this cartridge a lot, but research goes only so far. In stating that I would primarily use "heavier" bullets i was talking shortcut because, in a given caliber, heavier normally equates to longer unless the bullet is of unusual weight for its length.

    I should have gone on to say that I expect mostly to be shooting at 200 to 300 yards at targets and using bullets of 100 grains or more, but at times will srep down to mid-weight bullets and shoot at shorter ranges - silhouette and wherever the coyote or bobcat shows up. Thanks too for the info from Shilen - it tends to confirm my inexperienced thinking. Which was, that if I back off a bit from 1 in 8" I will probably not lose much stability for bullets over 100 grains and may avoid over spin for the mid weight bullets. At least I hope so.

    If you see any weakness in this thinking, please advise.

    Thanks again,
    CCCC
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  • Hawk CarseHawk Carse Member Posts: 4,381 ✭✭✭
    edited November -1
    I don't think you can "back off a bit" and "not lose much stability" except right at the ragged edge. Normally a given barrel-bullet combination will work or not. There are a few exceptions right at the ragged edge. A friend has a 9 twist .223 barrel installed when 69 grain bullets were the heaviest available, and very accurate with them. It will stabilize 75s but they are not as accurate. Gives him a choice of better grouping capability or less wind deflection but not both at once.

    I checked a couple of other manufacturer's twist charts. Lilja's recommendation for their barrels is similar to Shilen's. Berger says their 95 grain VLD bullet is ok in a 10 twist but their 105 requires an 8. They do not make a 100 grain VLD.
    On the other hand, JLK also makes VLD bullets and they say a 9 twist is adequate for their 105.
    If you want to load Sierras, they will talk to you about such stuff on the phone.
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  • JustCJustC Member Posts: 16,056 ✭✭✭
    edited November -1
    8 twist is indeed best for the heavy match pills, but that is considering putting some ground under them as well. I have an 8 twist 6.5 barrel that will shoot better at 400yds than at 100,200,or 300 yds. The bullet seems to stabilize after 300yds. That is fine, since it is a 600-1000yd gun.

    Your choice of 9 twist for 100-300yds is probably a good idea so as not to impart as much stress on the bullet jacket as well as to stabilize it at a shorter distance from the muzzle. If I use a 6br for 600yds, it will be 8 twist, but for 300yds, a 9 twist. MHO
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  • CCCCCCCC Member Posts: 10 ✭✭
    edited November -1
    Thanks so much to Hawk Carse and JustC for responding with these comments and details. Your experience counts for a lot - and as a hunter who also reloads and tries to get every rifle down tight (but have not been a competitive or extreme long-range shooter) my experience is limited in these tech matters.

    The bullet mfg. info you included is quite helpful and I will call Sierra, because I have used theirs quite a bit. In the end, and once this rifle is together, it will be the same us usual - working to find the best bullet/case/powder and load/setup combination.

    Consequently, I wanted to try to start at the best place because am only going to build one of these rifles and this will be the ONLY barrel I buy - that is why I inquired of the experts. Thanks again,
    CCCC
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