Hi Crouch:
Jason is correct, there are lots of ways that will accomplish what you need. Here's mine to add to the list:
I usually look at several loading manuals, do some forum searches, etc. to get an idea of what other people are using in the caliber I'm going to load. As a generality, I find that loads listed in newer manuals tend to be fairly mild in my rifles. But you must know that there are so many variables between actions, barrels, chambers, dies, etc. that you must start below listed or posted loads and work up to what will work in your particular rifle.
I then take a resized case from the rifle I'm loading for, cut a slit down the length of the neck with a fine hacksaw blade, and keep for future use. Then I neck size it, pick a bullet I'm going to use, just barely start it into the case, and then carefully chamber it in the rifle.,Note that this is an unprimed, empty case.) Then I carefully measure the base-to-ogive,BTO) case length and repeat this with 3 bullets from the same box, neck sizing the case in between. I average these 3 measurements to get what I call "soft jam" or the point where the ogive of the bullets just touch the rifling. I record this info in my notes for this caliber/bullet combo. Do this for each bullet you plan to use.
Next I plan the powder charge by picking what appears to be a max. load for the bullet/powder/primer I'm using and back off at least 10%. Say it's 6 BR and a max. load is 34.8 gr. of Varget. 10% will take to to about 31.3 gr. I then load 3 loads each, at the length determined as "soft jam", in 0.3-gr. increments up to 0.9-gr. ABOVE the max. load. In this instance, you would load at 31.3, 31.6, 31.9, 32.2 ... etc. up to 35.5 or even 35.8.
Remember that every gun varies and you must keep a close eye on your cases when you are shooting these loads for any sign at all of high pressure. Normally you will see severely flattened primers first, but if you take a mic to the range you can also measure the base of the cases and keep an eye on the expansion there. It also depends a lot on whether you have a factory SAAMI chamber or custom. It will help if you can monitor the wind, but shoot these test loads with the best of your ability to shoot small groups and save the targets for future reference.
These loads will clearly you show a load or range of loads that do best in your rifle. Take those best loads and do the 3-shot loads again varying the BTO from .015" off the lands,"soft jam" minus .015") to .015" into the lands in steps of .005". This sounds like a lot of shooting but remember that you are really fireforming cases to your chamber as you do this. The groups you get from this series will also clearly show you what seating depth your bullet prefers.
Now you have excellent data to take the best of the best of these two test series and fine tune them to the "hummer" load for your rifle.
There are many ways to accomplish this, including using computer data as Moderator says above. But I'm an old-time reloader from back in the '60s and I firmly believe that shooting test loads is the best way to go. You learn good loading skills, good shooting skills, good data recording, have more fun than should be legal, and grow to know your rifle and its abilities and your skills will be the better for it. Clean your barrel carefully, completely, and regularly. Forget the baloney of shooting out your barrel. Barrels are made to be shot and there are guys all over the country winning matches with barrels with 3,000 to 7,000 rounds through them. A barrel definitely has a "lifetime" and when the end of its life comes it's just an opportunity to buy a new one and start all over again.
This is way too much fun!
Edit: Yes, what an oversight that I did not mention bullet weight. I do so much shooting with 66-/68-gr. bullets that it just becomes "accepted" in my thinking. The loads suggested above are all with 68-gr. or lighter bullets.
