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I use a cleaning rod. Close bolt run rod down barrel till it hits bolt face, mark rod. Next take bullet you are using drop it into chamber and hold against lands with eraser end of pencil, run rod down barrel till it hits nose of bullet and mark the rod. Then just measure between the marks on the rod. Make sure you have something flat threaded on the cleaning rod so the tip of the bullet does not go inside of the hollow rod.
I use a stoney point overall length gauge which was bought out by hornady. It is now called the Lock-N-Load O.A.L gauge. Cabellas and most all sporting goods outfits that sell reloading supplys carries this little goody. They are about 30 dollars. They are very easy to use and plenty accurate. You need a 6 inch dial caliper to go with it.
I load a round long, with no crimp and chamber it. Use a sharpie marker to verify it touched the lands and moved in the case. Then back it off 30thou and start working there.