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Posted: 1/16/2009 5:04:12 AM EDT
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How close do you get your finished rounds. My goal is .005" is that reasonable or not?
If you have bullets that very in length, do you try to get the finished round to the same length or do you accept a difference of .012"? I have some Win FMJ 55gr and they vary quite a bit. I got them all the same length by adjusting the bullet seater. Should I do that, or just set the seater and let the bullets sit where they end? Thanks. |
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Forget about 0.005. Some bullets will vary by 0.020 to 0.040 or even more in length.
The seater pushes on the ogive of the bullet. That means every bullet is seated the same depth into the case. For uniformity, this is more important than the cartidge overall length. If you measure the length from the case head to the bullet ogive with a comparator, you'll find very small variation. Magazine length ammunition must take this variation into account. I load AR ammunition to 2.26 inches overall length and let it sneak out to 2.265 inches or so due to the variation in bullet length, but many shooters are not comfortable with that and load all magazine length ammunition to 2.25 inches (maximum, some bullets want to be loaded to lengths closer to 2.22 inches). I have one commercial magazine that will not accept a 2.26 inch long cartridge, but all of the USGI magazines work fine and I've never had a feed problem. |
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Read this current thread to learn about one make of comparator. There is a link inside to a very good article at another site that will teach you how to use the tool.
http://www.ar15.com/forums/topic.html?b=6&f=42&t=266323 You probably don't need to worry about using this tool. If you load to 2.25 or less cartridge overall length, you probably won't care about this tool. If you load the same bullet always, you may not need to worry about the variation in the length of bullets affecting set up of the seater die; the HPBT match bullets tend to be the worst in this regard, and out of a single box the variation is as bad as the bullets I buy as seconds. A USGI AR magazine will accept a cartridge 2.27 inches long, barely. If you have cartridges that end up longer by just two hairs, they will drag. Loading to 2.26 inches gives 0.010 inches of leeway to soak up that variation of bullet length, and 2.25 gives 0.020 inches. I seriously doubt you will ever run into a problem at that length. Forget about the potential problem altogether at 2.22 inches. A detail to watch for- If you load compressed loads and the neck tension is not sufficiently tight, the compressed gunpowder will push the bullet out of the case. Sometimes it's noticeable, and sometimes you will need a caliper to see the difference. Depending on how far the bullet unseats and the use you plan for the ammo determines what you will do next. It might be nothing, it might be reseat and shoot the ammo right away, reseat and add a little crimp, or break the ammo down and rebuild. |
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