distance to rifleing
You can buy all sorts of guages to determine bullet seating depth.
Some rifles shoot better when the bullet is touching the lands and others like a jump, you have to find out what your individual rifle prefers.
One way to find max length is to slightly neck size a case, seat a bullet (UNPRIMED & NO POWDER) as far out as possible, feed it into the chamber and close the bolt, it will be very tight to get out but with care you will succeed. You will have found the maximum overall length for your rifle but always refer to your calibre spec for the max reccommended. NEVER FIRE A LOADED ROUND IF THE BOLT FEETS TIGHT WHEN YOU CLOSE IT.
From there you can load up batches of live rounds (3-5 at a time) with the bullet seated a few thou deeper for each batch, eventually you will find what seating depth your rifle prefers.
ALWAYS CHECK YOUR CASE LENGTH & TRIM IF IT IS LONGER THAN RECOMMENDED.
Failing that, buy a RCBS Precision Micrometer.
REMEMBER CARELESS RELOADING CAN BE FATAL, YOU DO IT ALL AT YOUR OWN RISK, the method decribed above worked for me until I eventually bought a Precision Mic.