250gr A Tip in a 308

Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by APGE, Oct 6, 2019.

  1. APGE

    APGE

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    Hi Folks,

    I don't want to throw the money at a failed experiment, but quickload says a 308 should be able to get a 250gr A Tip to 2400fps. At that speed Applied Ballistics says 5.25 minutes drift in a 10mph win at 1000 yards.

    Very impressive figures for a 308 - pretty well as good as any F Open cartridge.

    Recoil would be high, torque unparalleled and cost very high, but if you had deep pockets and could tame the beast you'd be a quantum leap ahead of the competition on a windy day...

    Anyone game to try it?
     
  2. Fred B.

    Fred B. Gold $$ Contributor

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    You need 9 twist barrel. I did pressure test (4831SC, .5 grain increments) with 230 g in my 300 WSM, got it to 2895 with no signs of pressure at all. Good groups at 1000. But it is a 10 twist barrel and I had keyholes at 50 yards.
    Checked 100 bullets and BTO was +/- .0005.
     
  3. cmillard

    cmillard

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    I think you will need faster than a 9 twist if it is for a .308 win
     
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  4. Ledd Slinger

    Ledd Slinger Gold $$ Contributor

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    It would be even more expensive because you would need a rest that could give you the trajectory angle of an artillery cannon to get to 1K. Lol.
     
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  5. ebb

    ebb

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    What is the time of flight at 1000 yds?
     
  6. APGE

    APGE

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    According to Applied Ballistics 1.556 seconds

    For comparison a 200 hybrid at 2650 has a time of flight of 1.553 seconds, so pretty much the same
     
  7. APGE

    APGE

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    Again, using the Applied Ballistics app, it's telling me a 250 A Tip at 2400fps will need 32 minutes of elevation from a 200 yard zero and a 200 hybrid at 2650fps will need 30.25. Not a lot in it.

    I'll stress that I'm not going to invest in trying this, but it is an interesting exercise on paper and I'd like to see someone else try it.
     
  8. RDavies

    RDavies Silver $$ Contributor

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    I don't shoot F/TR, but I do know a few people who have tried 230gn bullets in 308, but ended up going back to 200s or maybe 215s due to excessive vertical. My thoughts are that the heavier bullet, with more time spent in the barrel in the little 308 makes handling with the lighter F/TR guns even more critical. On paper they had less wind drift, but never consistently scored as high as when they used the lighter bullets.
    The long barrel times is a lot of the reason why rimfire BR shooters claim that bag/rest/stock setup is so critical even with their little light pills.
     
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  9. Fred B.

    Fred B. Gold $$ Contributor

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    It is not more costly all considered.
    Yes, it cost maybe $30 more per 100 than burger. But it save about 3 hours of prep time and you won’t have a pile of rejects after sorting them.
    I think it will show up at bench rest matches very soon since we can use muzzle brake and reduce torque/recoil.
     
  10. APGE

    APGE

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    That makes a heck of a lot of sense. I do wonder if you had enough time and money whether with (lots of) practice you could get the requisite technique sorted. I don't have enough of either, so I'm really doing nothing more than spit balling
     
  11. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    2350 fps is probably a more realistic velocity for a tuned load with a 250 gr bullet in a .308 Win case. The first question I would ask is what would you be trying to do with it and why do you think the 250 gr A-tip would be the optimal choice? As an exercise, you can run the numbers in a ballistic calculator such as JBM for heavy .308 bullets in tuned loads of of known velocity. For example, reasonable velocity estimates for tuned loads from a 30" barrel with the 200.20X, 215 Hybrid, and 230 Hybrid bullets over Varget in Palma grass are 2650, 2550, and 2450 fps, respectively. Using box BC G7 values of 0.328, 0.354, and 0.368, with atmospherics of 70 degrees F, 1000 ft elevation, 60% humidity, and 29.94" Hg, JBM wind drift estimates for a full-value 10 mph wind are:

    600 yd
    200.20X = 3.3 MOA
    215 Hybrid =3.2 MOA
    230 Hybrid = 3.3 MOA
    250 A-Tip = 2.8 MOA

    1000 yd
    200.20X = 6.2 MOA
    215 Hybrid = 6.0 MOA
    230 Hybrid = 6.1 MOA
    250 A-Tip = 5.1 MOA

    Someone may claim to be able to obtain more velocity for one these bullets. Yes - that's certainly possible, but the velocities values given are reasonable values for tuned loads that have actually been used in F-TR competitions, and any increases in velocity aren't likely going to be huge.

    So what does this exercise really tell you? My first take away is that neither the 215 or 230 Hybrids are going to be a huge advantage in wind deflection in a .308 Win F-TR rifle over the 200.20X bullet. First and foremost, I don't think the .308 Win case has sufficient boiler room to push those bullets at velocities that will take full advantage of their BCs. In addition, even the very modest gain in terms of decreased wind deflection exhibited by the 215 Hybrid over the 200.20X assumes they can be loaded and fired with equal precision. That may or may not be the case. I know a few F-TR shooters that tried the 215s and went back to the 200.20Xs due to vertical issues. Whether those issues were caused by recoil management (gun handling) problems with the heavier bullet, or arose from marginal stability at the relatively low velocity obtained from a .308 cartridge doesn't really matter. Dropped points are dropped points, so a slight increase in wind resistance may not always overcome the other problems that may arise when switching to a heavier bullet. I think it's pretty fair to state that 215+ gr bullets in the .308 Win are not for everyone.

    Clearly there are important questions to answer before going down this path. Few people will already have a .308 set up optimally for the 250 A-tips. I'm guessing they would require somewhere in the neighborhood of a 9-twist barrel (certainly faster than a 10-twist) to achieve the full intrinsic BC. They also probably need something like a 0.300" freebore (or thereabouts), meaning a rifle set up to take advantage of their high BC would likely not be realistically usable with any other lighter bullet/powder combination. So such a setup would necessarily warrant a purpose-built barrel.

    So we're talking about a custom barrel setup, and a new finishing reamer (or Uni-throater), and really no idea how it would actually shoot because that's pretty much uncharted territory. I'm not saying there isn't anyone that could get it to work, but I've recently been down the experimental uber-high BC bullet route, and I know from experience that it can turn into a real black hole. If you want to give the 250s a go in the .308, I think it'd be an awesome experiment to try and my hat's off to you. Just be aware at the start of what you might be getting into and make an informed decision of whether it's worth the effort.
     
  12. APGE

    APGE

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    A great, detailed post as always, Ned!
    FYI The 2400fps was an OBT node, so it could very well tune at that velocity. It was however at 64k psi

    Do you care to share the details of your "uber high BC bullet" endeavours?
     
  13. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    I'll share the most important detail about my recent exploits with uber-high BC bullets: they have uniformly been black holes...gaping, bottomless, empty pits...devoid of all life, or even a feeble flickering spark of happiness; once you have irreversibly crossed that event horizon, they inexorably draw you down, down, down, down...into utter oblivion. They can also have a similar effect on your wallet. Hence my reason for advising making an informed decision about trying a new bullet that also likely requires a dedicated barrel and chamber for optimal results. It's great when such an endeavor pans out, not so great if it doesn't.

    I agree that with sufficient freebore, a 30"-32" barrel, and the right powder, 2400 fps is probably achievable with a 250 gr bullet in .308 Win. But it would likely be running in the 64K+ psi range as you noted, and the increase in recoil would be commensurate. It might work well for some, but given that I am not aware of more than possibly a single F-TR shooter that has ever successfully used the 230 Hybrids for any length of time in competition, I am more inclined to think a 250 gr bullet is asking a little too much from the .308 Win cartridge.
     
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  14. Down South

    Down South FTR Junkie Gold $$ Contributor

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    ^^^^ This ^^^^
     
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  15. Zero333

    Zero333 Silver $$ Contributor

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    I would not bother. That's too heavy for a 308win.
    I tried 210's in a 308 and could not get a decent water line at distance.
    200's are about the reasonable limit.
     
  16. Down South

    Down South FTR Junkie Gold $$ Contributor

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    I'll agree with this for the most part but I did have a 210 gr JLK load in one particular barrel that held super tight vertical at 1000 yards in FTR. To this day it was the best load I've had in any of my barrels, ever. The last couple barrels I've had prefer the 200s but that one particular barrel was a laser with those 210s. It shot 6 1/4 inch vertical for 24 shots (4 sighters included) at 1000 yards and set the national record at the time (200-13X) in FTR. I wanted to cry when that barrel was done.......lol
     
  17. Zero333

    Zero333 Silver $$ Contributor

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    I also has a 308 win barrel that shot the 208amax at distance better than any other bullet.

    In this game there are always exceptions to the rules.
     
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  18. LA50SHOOTER

    LA50SHOOTER Silver $$ Contributor

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    Nope - Not in a 308 Win. = "The Little Train that Can't" (IMO)

    - I'm going to try the 230's & 250's (A-Tips) in a 35" 30-378 Weatherby chambered barrel (Has a custom throat that was set for 230 gr. Berger hybrids) and see how they do. Possibly also in a 300 RUM (230's) and the 230's possibly in a 300 Norma Mag. Imp.

    - Ron -
     
  19. davidjoe

    davidjoe Skunkworks Gold $$ Contributor

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    500 250’s arrived a month ago, finally, but at a busy time. I had originally planned to test these in a very unique .308 and still may.

    The anticipated powder to bullet weight ratio in this particular combination is depressingly low in the F-Class arena but on the other hand the .308 case is bigger than we credit it when the COAL is not limited by any rule.
     
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  20. FrankG

    FrankG

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    I’m going to say no to a 1-9 twist for the 250 ATIP. I’m running a 1-9 twist and have shot the 225 ELDM, 230SMK and the 230 ATIP’s and all have shot excellent. Only shot the ATIP to 430 yards so far. I’m running them out of a 300PRC at 2900fps.

    The 250 ATIP per Hornady need a 1-8.5 twist minimum. According to my twist calc’s I’d go with a 1-8.25 or even a 1-8 twist.

    A 308win and at lower velocities and now throw in temperature/environment conditions being a variable.....a 9 twist won’t be enough in my opinion.

    Later, Frank
    Bartlein Barrels
     
    Last edited: Oct 15, 2019

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