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I've got a Ruger #3 (1978) that has considerably more free bore than later models. What is the approximate COL for best accuracy best accuracy in the mid 70's Ruger #3? I am loading 405 grain hard cast and 350 grain Hornady JSP bullets. Thanks
We need bit more information. First, what cartridge is the rifle chambered for? By free bore, are you referring to the length you need to seat bullets in the brass for the bullet to touch the lands?

Not knowing the round count through your chamber means we do not know how far down the barrel your lands have retreated over the years. A good way to discover this is to seat a bullet long enough in brass (no primer or powder) that it will not allow the action to close. Then press the bullet deeper into the case in small increments until it will just seat all the way into the chamber, allowing the action to close. Measure that length and you will have the maximum COL with that design of bullet.

Finally, I will say, you will need to do load testing and cartridge length testing to learn what your rifle needs for best accuracy. One rifle wants the bullet to touch the lands. Another rifle wants a bit of space left between the bullet and the lands. There is no rule of thumb for even so called identical rifles, right off the assembly line.

Now change to a different bullet design and you need to start all over testing different lengths, because it is the length to ogive (where the bullet reaches full diameter) rather than over all length, that decides how a cartridge will fit the chamber.
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