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Oal and seating depth?

Discussion in 'Ammunition & Reloading' started by bt97006, May 1, 2009.

  1. bt97006

    bt97006 Aloha Member

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    Ok, I'm a rookie here and any advice is greatly appreciated. I've done a few searches on this topic and my reloading manual has a short explanation but I still come up a little befuddled. I understand all rifles are different and each has it's own distance to lands in the throat of the chamber. I have read that each gun has an optimum distance to which bullets are seated to give good accuracy. What tools would I need to find the best seating depth for my rifle and what is the proper way to check OAL on cartridges? Does case trim length play a big factor in seating depth and accuracy? Hoping a few veteran reloaders out there might enlighten me.
     
  2. rodell

    rodell Newcastle, WA Active Member

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    Case length is a component of seating depth, depending on the bullet, whether you crimp it, etc. The best thing to do is trim all of your cases to the "trim to" specification. If you're just getting started with brass and reloading, you won't have to trim them for a couple of reload cycles (unless you are shooting big bores or making Ackley brass).

    For determing your MAXIMUM cartridge length, there are several methods. The fastest is to expand the neck of a case and seat, but not crimp, a bullet way out. The bullet must be movable, but, not loose. Then, carefully chamber the round (no powder here). The bullet will be pushed back into the case by the lands. Remove the cartridge, carefully, and measure it with your calipers. Subtract .005" and that's your maximum length. (If there are deep marks on the bullet, you had too much neck tension. If that happens, open it up and try again. The marks should be very faint, but, should be there.) Remember, it will change if you change bullet type. The reloading manuals give an average OAL for the caliber, but, you now have "personalized data".

    Another method involves the use of the Hornady Lock-N-Load Gauge, made especially for this purpose. It was formerly made by Stoney Point and is available. You need a special cartridge case, orderable separately, for each caliber.

    Unless you know what you are doing, DO NOT MAKE A LIVE CARTRIDGE WHERE THE BULLET TOUCHES THE LANDS WHEN CHAMBERED. (Important emphasis, sorry. Dangerous pressure MAY result.) If you are going to be a precision benchrest reloader, this is done and you will need to use a slightly different technique that actually cares about how hard you hit the lands when measuring. At that point, you are also sorting bullets.

    While you will have determined the maximum OAL the rifle can take, you may be limited by your magazine. In some rifles, the magazine OAL is less than the chamber OAL. You can make a couple of dummy rounds at your OAL and make sure they feed properly.

    If you're loading for a Weatherby magnum in any caliber, use published data. Don't bother measuring the OAL - the freebore is so great it won't function in the magazine if you did make one at that length.

    To determine the optimum OAL for your rifle, you must load, shoot, load, shoot, repeat. It will be a combination of powder, bullet, primer length, and, of course, you have to do your part. A good place to start is to see what others have done for the same rifle model (not caliber). You can drive yourself crazy with all the powder / bullet combinations out there. Load small batches, varying only one thing at a time. Watch out for barrel heating and fouling. If you are looking for a benchrest or hunting load, you should test your loads like you would be using them. (For example, hunting loads are usually looking for best three shot groups out of a cold barrel, or, best first shot accuracy).

    Feel free to ask if I haven't been clear.

    Bob
     
  3. Southridge

    Southridge Orting WA. Member

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    The way they did it before the gauges came on the market is the way I have always done it and works very well.
    Take your trimmed case push a bullet in the case till it starts in, take a sharpie
    pen and color the end.close the bolt,and it will seat the bullet to were it is touching the lands & groves do this a couple of times just to double check.
    take your OAL and seat your bullet another 5 thousands deeper.
    then when you do it in your press make up a dummy rd. and check it.
    And by the way this is for a Bolt action. Good luck and have fun.
     
  4. bt97006

    bt97006 Aloha Member

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    Thanks that helps a bunch guys. I am reloading for a Howa 1500 in .223. I primarily shoot off a bench and use it for varmint hunting. I just knew i was missing that part to get the correct "jump" for the bullet into the rifling. I am still searching for what my gun likes best and have started to pay attention and take records instead of just blasting at a target as I have done in the past. I am really enjoying this new hobby of reloading. The more I learn about it and my shooting techniques, just makes it easier and that much better.
     
  5. rodell

    rodell Newcastle, WA Active Member

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    The faster your bullet is traveling when it leaves the neck of the case (and the faster it is accelerating) the longer the freebore can be.

    In all things, consistency is better when doing load development. You'll quickly find what works best for freebore. The hardest part is waiting for the barrel to cool - that's why two or more rifles are required!

    For that particularl weapon, you might also look for recipes on Weatherby's "Spike Camp" forums. Since the Vanguard is the same action, they may have some tips.

    Bob