do a search for the "split case method",..that is by far the best method next to spending the $20 for the stoney point tool. I actually bought the sinclair tool and like it the best of anything. Buy the tool and don't look back.

You can also seat a bullet wayyyyyyy long,..then try to chamber it. If it doesn't chamber,..seat the next one only a few .001"s deeper and try again. (don't use the same bullet twice,..you want to be able to see when the rifling marks dissapear) Keep doing this until one chambers with very very little or no rifling marks. Lock the die and that is ~your max OAL for that rifle.

The longest you can load is what the magazine will accept
unless you want to shoot single shot. Most of the new
rifles have a very deep throat so dont worry about it.
If you are going into benchrest competition then have
a custom barrel chambered to your specs. I have chambers
where the bullets jump almost 1/8 of an inch and still
shoot under one moa.
Lyle

Some of todays chambers are ridiculously long. The Stoney Point OAL Guage is rather inexpensive, and saves a lot of heartache. It'll take a while to get used to it so you'll have to take several readings until you get past the learning curve. Beware though that not every rifle will shoot best at its maximum OAL. est wishes.

Cal - Montreal