Seating depth for boat tail bullets in belted magnum cartridges

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Lee in OH, Apr 6, 2003.

  1. Lee in OH

    Lee in OH Well-Known Member

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    I'm needing to have my 264 Win. Mag. barrel throated. I neglected to tell the gunsmith how I wanted it throated (now I know better). [​IMG]
    When using boat tail bullets, would I be better off to seat the bullet so that the base of the bullet is flush with the neck/shoulder junction or so that the boat tail is beyond the neck/shoulder junction and the major OD of the bullet is .265" into the neck.

    The case is neck is .245" long and the boat tail is .145" long.

    The action is a solid bottomed single shot and the intended use of the rifle is for punching both paper and varmints (live) at long range from a portable bench.

    Thanks in advance...
    [​IMG]
     
  2. 4mesh063

    4mesh063 Well-Known Member

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    If it were me, I would not get it throated. In my experience, re-throating has no positive effect on the gun, and generally, creates too much leakage. My theory is, the "Shot Out" version is better. As you look at a throat reamer, I cannot immagine what that will do that will be better than the nice worn out rifling. If you feel that accuracy has dropped off and needs restored, I'd try shooting some bullets with a longer ogive on them first. Berger-JLK-... If you're still dead set on it, then go do it. Take as LITTLE as possible. Like prit-near nothin.
     
  3. Lee in OH

    Lee in OH Well-Known Member

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    The barrel is only about 100 rounds old. The smallest group I've gotten so far is 1.055" at 200 yards. I haven't done a LOT of group shooting with it though. If I can get it to .750" on a pretty regular basis I'll be satisfied. Perhaps I just haven't tried enough development yet. The SD on that load is 6. Maybe I'll just play with the seating depth some. I'm lightly on the lands now.
     
  4. Cybra

    Cybra Well-Known Member

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    Lee

    This topic was briefly touched upon over at Benchrest Central; Mike Bryant made a good suggestion that the shank base of the bullet should be just slightly ahead of the shoulder/neck junction. Why slightly ahead?--well, if you end up with a doughnut, it'll pinch a tad.

    I don't have that trouble, and seat my bullets exactly flush with the base of the case neck. Of course, it becomes rather expensive having reamers designed for the "perfect fit" every time. [​IMG] It doesn't drastically, aside from internal case capacity, matter how far the boat-tail portion of a bullet extends into the case, the shank is the part that forms the gas seal--try to keep that portion seated either flush or slightly ahead of the shoulder/neck junction.

    As far as accuracy itself is concerned, so long as the doughnuts aren't nailing you...the set-up you have now may work just fine. A lot of speculation goes on about pressure shock waves and stuff that gets DEEP <both technically, and the bullsh*t itself, so watch yer` step.> [​IMG] A throating reamer's about $65 or so, so if it's something that's really bugging you...have at it. Of course, to rechamber and all that...boy, unless we're look'n at a Big W special, I think I'd just live with the ooops. And stick to seating into the lands. [​IMG] Best of luck, partner. And don't feel bad; I once screwed myself on a $4000 rifle...yes sir, I made a flaw in some measurements, and later determined I would've preferred a different seating depth. Awl, well....it's only money <and a tad of pride, not to mention <gulp!> accuracy. [​IMG]
     
  5. Lee in OH

    Lee in OH Well-Known Member

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    I've decided to go ahead and shoot it as is and find the best load I can. With very preliminary load development I've found a load which shot 1.055" at 200 and has an SD of 6. I'm not sure if it's repeatable or not, but with an SD of 6 it should do pretty well.

    Bear in mind, this is not a tight-necked chamber and the action is a factory Savage that has not been trued at all.

    With this setup, what would you say I should reasonably expect to get as far as groups after some load development. Is .5" at 200 too much to hope for????