Ok, did a test run tonight.

Put the primer in a shell pretty easy with the hand primer.

Then I played with seating a few bullets without primer or powder.

Did some more reading on seating the bullet and think I've got the right idea on what to do. Don't exceed the COL, but the actual depth will vary depending on my rifle.

Went above the length of a factory bullet, but under the COL and it seemed to chamber fine.

I will make up a few of different lengths and see how they shoot.

Am I thinking right or wrong?

Take and seat a bullet to the max overall length as manuel dictates(unprimed case please). Chamber cartridge and closed bolt,remove and measure the "new " overall length. Should be shorter than before chambering, hopefully. If so, this means than the bullet went tight to the lands & grooves and seated itself tight.
Measure and record this overall length for that particular bullet type,weight and make..
Now you know exactly where that bullet sits so you work from there. Every time you change loads,everything else has the potential for change including pressures. But I doubt that once you develop a load perfect for you and your rifle, neither one of you will want to change.
I would be starting my tests with bullets seated 010"(thousanths) from lands with increment changes of .005" out to no further than .030". with powder charges not at all near maximum.
The deeper the bullet is seated from the lands/grooves, the higher the chamber pressure. so we really want to take this slowly.
Factory cartridges are light loads for the above reasons. God only knows where the buletls sits from chamber to chamber in God know what.

What calibre are you reloading as I assume it is one of the more common modern ones ?

Don't forget. If it's a hunting load. It needs to fit in the magazine, comfortably and you don't want pressure problems in the field. Higher or lower altitude. Hotter or colder day, etc...will change the pressure. .005 - .007 off the lands is usually comfortable. I did say usually.
Called OAL will typically fit the factory magazine and the chamber is typically cut to fit the called OAL but ALWAYS check.
When I set primers I set them with one squeeze. Rotate them 90 degrees and give them another squeeze. I do this to square them up, in the pocket.

Ok, time for a very basic question - where are the lands on a rifle? How do you tell when the bullet is seated just short of them?

Inside the barrels of handguns and rifles are spiral impressions called rifling. The raised portions of the rifling are known as lands and the recessed portions are known as grooves. When a weapon is fired, these lands and grooves cut into the bullet, putting spin on it as it travels through the barrel of a firearm. Because bullets have an oblong shape, spin is necessary for accurate flight.
As I mentioned, if you seat the bullet by forcing the cartridge into the chamber , you know that the bullet is tight to the lands and grooves as it simply can't go any further. Remove cartridge,measure and record . If you then place cartridge in press and with your sizer die seat bullet deeper(I believe a half turn on the seater screw will give you about .005" depth) and that is the distance the bullet is from lands & grooves.

Hammer1 - thanks. It is now all clear

CVC,

A very simple way to get the proper seating depth to start with is to drop a bullet into the chamber. Next run a pencil into the chamber, eraser first, and hold the bullet to the lands. Next take a cleaning rod with a plug on the end and run it into the muzzle and up to the bullet. Do it lightly, and mark the cleaning rod at the muzzle with another pencil. Now take the bullet out of the chamber and re-instal the bolt. Run the cleaning rod again into the muzzle and all the way to the bolt face. Mark the rod again. Measure the distence between the marks and seat a bullet into a case that deep. Will take several seating strokes as you want to start long. Once you get the right OOL, turn the seating plug down maybe one turn more and you'll be just off the lands.

If that sounds confusing, send me a PM and I'll send you my phone number and walk you thru it. Once you've done it, you won't believe how easy it is.

Loaded my first cartridges tonight. Maybe I'll get to the range tomorrow and try them out.

Thanks everyone for your help.

Keep us advised on how you do ?

This is how I measured mine.