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11.25 twist

Discussion in 'Rifle Country' started by mturnbull333, Jun 10, 2011.

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  1. mturnbull333

    mturnbull333 Member

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    I just bought a LWRC REPR 308 with a 18 inch barrel and a 11.25 twist rate,what is my best bet for bullet grain. I would like to get out to a 1000 plus yrds.
     
  2. Owen Sparks

    Owen Sparks member

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    How long is your barrel?
     
  3. LoonWulf

    LoonWulf Member

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    id suggets match grade 168s. 1k yds is one hell of a lob with a 18" barreled 308. 168s are likely gonna be launching at less then 2600.
     
  4. Jim Watson

    Jim Watson Member

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    168s won't cut it, certainly not out of one of those short barrels.
    Most available is a 175, a 155 gr Scenar, VLD, or Palma might be better.
     
  5. dprice3844444

    dprice3844444 member

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    se fla i love claymores 01/sot
  6. mturnbull333

    mturnbull333 Member

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    Is 1k yds to much to ask out of a 308 with a 18 in barrel?
     
  7. LoonWulf

    LoonWulf Member

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    No its not, and the platform is most likely accurate enough to be fun at that range. but it IS a long shot for that gun and cartridge consistant hits at 1k will take alot of work. Your bullets are gonna be starting 100-200fps slower then list, and the 170-180s most people would chose are going to be in the 2500 fps range if that. Again drop can be figgured, but reading the wind is going to be the real trick. ahh i also forgot to mention im unfamiliar with the 155grns if they offer better bc then the 168s ive used then they might be the best choice.
     
    Last edited: Jun 11, 2011
  8. TonyAngel

    TonyAngel Member

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    I really don't know why, but the 168s seem to run out of gas at around 600 yards. Maybe it's because the BC gets too low at the velocity they are moving at that distance. With an 18" barrel, I would think that going with a heavy bullet that doesn't need all of that velocity would be the way to go, which leaves you with the 175s or maybe heavier.

    .308 is not the best platform for shooting out to 1000, but that's what makes it interesting. Like Loonwulf said, getting there isn't going to be the problem, reading the wind is. With a 2500fps or so muzzle velocity, the bullets is going to have a long flight time.
     
    Last edited: Jun 13, 2011
  9. ripp

    ripp member

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    he is not going to touch 2600 fps, without massive pressure problems AND a perfect baerrel, with 175 grs loads, 2400 fps maybe. 155's, 2550, maybe.
     
  10. mturnbull333

    mturnbull333 Member

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    Thx for all the comments it will be fun getting there
     
  11. TonyAngel

    TonyAngel Member

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    Just don't blow yourself up doing it. You don't want to beat your rifle to death trying to do it either.
     
  12. Zak Smith

    Zak Smith Moderator Emeritus

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    2010 Steel Safari.. high .308 was 5th overall shooting M118LR from a suppressed 20". 175's. Very talented shooter. Would not recommend Sierra 168's for this.
     
  13. Kerf

    Kerf Member

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    mturnbull333

    I don't think it's the 18" barrel that will give you the most problems at 1000 yards, but your mention of the 11.25" twist of the barrel. A slow twist barrel like that is set up for a shorter, lighter weight bullet in .308. I think the 308 cartridge is going to have a problem pushing a 168 gr. bullet fast enough to stabilize it out to 1000 yds. Correct me if I'm wrong, but most barrel manufactures use a 1-9 or 1-10 inch twist in their standard barrels. So, a 1-11.25" twist would be considered slow, i.e., bullets with a short bearing surface.

    Think the 6.5X55 Swede and the .244 Remington.

    Kerf
     
  14. Zak Smith

    Zak Smith Moderator Emeritus

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    Most match barrels are 1:10 to 1:12 for .308. In my experience 1:12's shoot 175's just fine, along with 155's. There is nothing wrong with 1:11.25
     
  15. USSR

    USSR Member

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    +1. I shoot 190SMK's in my 1-12" twist FN SPR all the time. Personally, if I had an 18" barrel in .308 and wanted to reach 1k, I would shoot the 155gr Lapua Scenar and try to reach 2600+ fps.

    Don
     
  16. TonyAngel

    TonyAngel Member

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    Yeah, the 11.25 twist rate is pretty popular right now. That's what I think the 5R barrels come in. It really shouldn't present a problem shooting 175s.

    USSRs opinion about shooting the lighter bullet is interesting, because my knee jerk reaction was that a shorter barrel would benefit more from shooting a heavier bullet at lower velocity, since there is so much less barrel to burn powder in. My theory is based on my belief that the heavier bullets don't need as much velocity to maintain their higher ballistic coefficient.

    I suppose the only way to be sure would be to try both. BTW, if the price of the Lapuas scares you, you can try the Sierra 155gr Palma bullet. I've had pretty good luck with them, but you really have to zing them.
     
  17. USSR

    USSR Member

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    Tony,

    The 155gr Scenar's advertised BC is .508, while the 175SMK's is .505 - essentially the same. Since the 155 can be driven at a higher velocity, advantage 155.

    Don
     
  18. Zak Smith

    Zak Smith Moderator Emeritus

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    This statement doesn't really make sense mathematically.
     
  19. Sebastian the Ibis
    • Contributing Member

    Sebastian the Ibis Member

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    I know less about long range rifle shooting that Zack and USSR have forgotten after a two beer bender. However this webpage explains it pretty well:

    http://www.6mmbr.com/308win.html
     
  20. helotaxi

    helotaxi Member

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    It's mostly an issue with the 168 SMK. It has a stability issue in the transonic region. The A-Max does not have such a problem. That said, heavier bullets have an advantage at longer range thanks to their generally better BC. That 11.25:1 barrel should be fine with the Hornady 208s which are about as good as it gets.
     
  21. Zak Smith

    Zak Smith Moderator Emeritus

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    Compared to a very heavy, but high BC bullet like the 208 or 210, you can push a 175 or 155 fast enough to basically have the same wind drift but 20-35% less drop, usually.
     
  22. pdd614

    pdd614 Member

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    USSR
    The 155 scenar bc is actually much lower than .505. Lapua updated the all the scenars to a more real world bc, for the 155 is now listed as .460 g1. The 175 smk is right around .495 g1.

    Check out lapua's web site. Even the almighty 6.5 cal 139 scenar is been downgraded to a lower .578 g1, 123's are at .527 g1.

    Sorry for going off topic, just wanted to correct a small mistake on the 155 scenars. They shoot fine in even 12 twist barrels.
     
    Last edited: Jun 15, 2011
  23. helotaxi

    helotaxi Member

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    The numbers don't bear this out at any kind of range. Running the 155 A-Max at 2700fps, the 208 A-max at 2400, the 208 exhibits 0.7" less wind drift at 200yds and it only pulls away from there; 5.8" at 500yds. Drop is a little bit less with the 155 (about 12% better), but at a known distance that is largely irrelevant since drop is very easily calculated and completely predictable. Wind is the important variable to eliminate for the simple reason that it is the largest unknown and can vary greatly over the bullet's flight. You'd have to push the 155 to 3175fps to get the same wind drift at 500yds and the 208 (at 2400fps) would pull away again past that distance.

    The 178 BTHP Hornady isn't even in the running.
     
  24. Zak Smith

    Zak Smith Moderator Emeritus

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    Using (old) published BC values
    Code:
    
    _Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
    175 load          0.51* 2700 >    0.00    2.62   11.18   26.93   51.55   86.72 | wind (inches)
    155 Scenar        0.508 2925 >    0.00    2.28    9.69   23.24   44.21   74.16 | wind (inches)
    210 VLD           0.617 2450 >    0.00    2.39   10.08   23.97   45.14   74.55 | wind (inches)
    
    175 load          0.51* 2700 >   -0.00    0.51    2.12    4.17    6.72    9.90 | drop (mil)
    155 Scenar        0.508 2925 >   -0.00    0.40    1.72    3.42    5.50    8.06 | drop (mil)
    210 VLD           0.617 2450 >   -0.00    0.65    2.54    4.84    7.59   10.86 | drop (mil)
    
    Note wind basically identical 155 vs 210, but drop 2.8 mils less at 1000.

    The 175 and 155 loads are actuals. The 210 is a guess for MV. If you could shoot the 210gr VLD at 2550, it would look like this (a little more favorable to the 210)
    Code:
    _Bullet_           _BC_ _MV_         0     200     400     600     800    1000 | YARDS
    175 load          0.51* 2700 >    0.00    2.62   11.18   26.93   51.55   86.72 | wind (inches)
    155 Scenar        0.508 2925 >    0.00    2.28    9.69   23.24   44.21   74.16 | wind (inches)
    210 VLD           0.617 2550 >    0.00    2.26    9.51   22.60   42.55   70.39 | wind (inches)
    
    175 load          0.51* 2700 >   -0.00    0.51    2.12    4.17    6.72    9.90 | drop (mil)
    155 Scenar        0.508 2925 >   -0.00    0.40    1.72    3.42    5.50    8.06 | drop (mil)
    210 VLD           0.617 2550 >   -0.00    0.58    2.31    4.42    6.93    9.91 | drop (mil)
    
    I've written for years that wind is more important than drop. However, once you've sorted with that parameter, the next one to consider is the drop rate (to reduce the effect of ranging error). The drop rate of the 210gr load is 25% more than the drop rate of the 155 load at 1000 yards.
     
  25. USSR

    USSR Member

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    That's fine that Lapua went to a g1 BC rating for their bullets, but now you can't compare the 155 Scenar to the 175SMK, because I don't believe Sierra's BC's are g1. The point is, there's not a lot of difference in the BC numbers (whichever way you rate them) between the 155 Scenar and the 175SMK, and since the 155 Scenar can be run so much faster, it would be a better option in a short barreled .308. Just MHO.

    Don
     
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