What O.A.L. is Best?
by Duane Siercks
One of the prevailing questions fielded by the Sierra Tech's deals with seating depth or Cartridge Over All Length (O.A.L.) in relation to accuracy. A misconception that has a very strong following states that a bullet seated to touch the rifling or very close to touching will provide "best" accuracy. While this may hold true in a large percentage of firearms, it should not be considered an absolute. There are many firearms that will have throats long enough that touching the rifling will be impractical if not impossible. This can cause the O.A.L. to be so long that feeding car- tridges from the magazine impossible, creating a single shot out of your trusty repeater. Also many firearms will prefer that the bullets have some "jump" to the rifling as well as in most hunting situations it is recommended to keep the bullet from touching the rifling. This helps to avoid a bullet being stuck in the rifling and being pulled from the case when trying to unload a loaded cartridge. Finding the "sweet spot" with a bullet in your firearm can be achieved in a methodical fashion by establishing the maximum length possible for your firearm and bullet combination by establishing these three things:
1. Maximum O.A.L. with bullet touching the rifling - Determine at what length the bullet touches the rifling. We then know we will need to stay a little shorter than this length. 2. Magazine length - In order to allow the cartridges to feed from the magazine of our bolt-action or semi-auto the O.A.L. will need to be slightly shorter than the magazine box.
3. It is highly recommended that a bullet be seated so that it has at least one bullet diameter amount of the bearing surface in contact with the neck of the cartridge case. This helps to provide uniform tension as well as to hold the bullet concentric with the case and will help accuracy considerably.
Once these three things have been considered, we then can determine what would be the maximum O.A.L. for this bullet and firearm. Start working up loads with a powder that has been a good choice for the cartridge/bullet combo and seating the bullet to the determined max O.A.L., then look for the charge that gives the best potential for accuracy. When that charge is found, move the bullet back, making the O.A.L. shorter, by .005" to .010" and shooting again to see what difference this made in accuracy. It is not unheard of to end up with the bullet being set back by .030"-.050" depending on the bullet/cartridge and firearm combination and of course safe pressures. Having found the "sweet spot" for this combination go back and work with the powder some more to further tune the load. If a different powder is used, one would want to maintain your sweet spot O.A.L. and work up with the new powder.
i welcome any advice