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Old March 5, 2011, 02:34 PM   #2
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Join Date: January 14, 2011
Location: on the north side of DFW
Posts: 949
Cast bullets (called boolits, to differentiate between jacketed) generally should be sized .001 to .002 above bore diameter. You are correct, if you want to achieve best accuracy, and minimal to no leading, you should slug your bore to find out what size you need your boolits to be.
Factory swaged and cast boolits are generally sized to a middle-of-the-road size so that they will likely work ok in most guns of that caliber. It's a compromise at best. If you are going to put in the effort to cast your own, you should make them the size YOU need.
I have just now started using my first TL mold, for the 45-70, so I can't give you firsthand knowledge of whether ALL TL molds will allow you to shoot as cast, but I've heard quite a few shooters say that is the case. Just remember, if you are casting gas-checked boolits, they will have to be run through a sizer to set the check on the base. I have, in the past, used a lubrisizer and pushed just the base and check down into the sizer to "seat" the check, without sizing the boolit. Don't be afraid to experiment.
I have shot several of my boolits, in different firearms without sizing, depending on my slugged bore dimensions, and my boolit dimensions. Much of this is a "try it and see" kind of thing... there really aren't many hard, fast rules. You can probably get by shooting a boolit .003 or maybe even .004 over bore size with no problems, as long as you let signs of excessive pressure and accuracy guide you.
If you are shooting boolits from a revolver, the critical dimension is not so much bore size, as it is the diameter of the mouth of each chamber in the cylinder. The boolit has to be that diameter, or .001 over, or you will usually get very iffy accuracy, and some pretty bad leading of the bore. My wife's 38 snub Taurus has chamber mouths of .360 diameter, and I was getting some pretty bad leading in the first 3/4" of rifling when I used "store-bought" cast boolits. I'm now casting a SWC that is dropping right at .360, so I'm pan lubing them with no sizing at all. I'll do a report as soon as I can get out to the range.
Good luck with your venture into casting... it's an addictive, sometimes frustrating, most of the time fun, kind of addition to reloading.
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