The 2.710 is a SAAMI spec, Sporting Arms and Ammunition Manufacturers' Institute. SAAMI is a voluntary guideline that all commercial gun manufacturers, ammo makers, and reloading die builders choose to follow. It is what allows Remington ammo to fit in the magazine and chamber in Winchester rifles. If you also build your ammo to those standards your ammo will work well in any mass produced rifle. So this isn�t a bad place for a beginner to �start� just to get some confidence and get some rounds down the barrel.
Beyond that, I always start with a new rifle by measuring the inside length of the magazine. This will be one factor in determining the max oal of a cartridge. I take the mag length and subtract .020� as an absolute max cartridge length based on the magazine size. In some guns this will be the only defining factor because at this length you are still well off the lands, so no way to get closer to the lands unless you want to go single shot. If you find the -.020 is a problem then alter it accordingly, but that works on all my guns from 22 hornet to 375HH.
Example: On my 243 the mag length is 2.910, so based on mag length alone I know I can load any bullet to a max oal of 2.890 for functioning. Using 95gr ballistic tips they hit the lands at an oal of 2.789. So with this gun and this bullet the magazine is not a limiting factor, but on some guns it will be. In my case I choose to come back an additional .010 off the lands for an oal of 2.779.
I use the Hornady Lock n Load gauges to get these measurements off the ogive. Get them if finances are not an issue. But I�ll also say you don�t need to have these to �start� reloading. I reloaded very successfully for decades before these became available and probably 100s of thousands reload without them. As your knowledge and confidence grows you can decide if you want to vary from SAAMI and the reloading book suggestions.
This is how I did it prior to the gauges. Measure the mag and subtract .020. Take a sized case with no powder or primer, seat a bullet to the mag length minus .020. Take a lit match and hold it under the bullet ogive area, rotate the bullet and it will completely blacken the bullet with soot. You can also use a marker, a black erasable whiteboard marker works very well. Gently try to chamber the round. If it chambers with no land contact marks you are done. That means even at max mag length you can�t hit the lands with that bullet, the magazine length is the determining factor.
If it chambers but you see land marks then you want to seat it deeper. All my seating die stems are 28 thread or .036� per revolution. So if you turn the seating stem � turn you�ll get about .009 deeper seating. Do that until you don�t get land marks anymore. Wipe and re-mark or re-soot with each try. Doing this you will find close enough for hunting purposes without extra tools where the land contact point is. Then you can measure the COAL.
And no, seating the bullet deeper will not increase pressure. Seating it longer will. A bullet that has a long running start at the lands will not pressure spike as much as a bullet that is resting against the lands. Resting against the lands is like a barrel obstruction and the pressure will ramp quicker trying to get it obturated into the barrel.
Don�t know if any of this makes sense in writing.
SAAMI 243 drawing. You can see length range is 2.540 to 2.710. You need to be sure if you are using short lightweight bullets that you have enough neck bearing surface/depth to provide good neck tension.