Almost all firearm and ammunition or component makers(in the USA) are signatory to SAAMI specifications...Sporting Arms and Ammunition Manufacturers Institute...and almost all ammunition has cartridge overall length specs.
To keep away from Lawyer trouble, ammo and firearm makers AND reloading manuals keep what they sell fitting within those SAAMI specs. But if you look very close in most manuals, EACH bullet has a OAL associated with it.
I have a 17 Rem and shoot the 20gr VM's in it...the Hodgdon 2006 reloading manual calls for a OAL of 2.15"...my Shilen barreled 700 rechambered with a PT&G reamer won't shoot for doodly at that OAL...I have to seat that bullet out to 2.21" which gives a 0.160" "grip" to keep the nice bughole groups...my 375 H&H Savage with Horn 270 SP's seated out to max magazine capacity at 3.55" has a 0.552" grip...BUT...to get max case volume with the base of the bullet even with the base of the neck, a distance of 0.350", less than one caliber, I need to seat the bullet to 3.75" OAL and at that length it still doesn't touch the lands...I just single load the first round at 3.75" up the pipe and stuff the next three at 3.55" in the mag. I gain about 6-7 gr H20 more capacity with the longer round and about 50-75 fs more velocity which translates to an additional 175-250 ft lbs of energy. The additional extra energy on the first shot could mean the difference of the animal dying instantly or dying a little slower.
As a newbee I recommend keeping your ammo fitting those specs...as you get more familiar with the sport you will learn the ins and outs of bullet seating.
One caliber seat is good...but you will learn there is many variations on that theme, the same as variations on crimping, seating out to "touch the lands", pressure/velocity and all the rest.
Part of "the neck grip" is to keep bullets from being pushed back into the case due to banging against magazine walls or in tubular magazines...but in a single shot all that is required is enough grip to keep the bullet from being moved due to handling. Some even seat the bullet well out, use a light grip...0.001" or less neck squeeze and let the lands push the bullet back when closing the bolt.
Each caliber seems to prefer a specific "to the lands" jump, but this isn't cast in stone...and many cartridges have a prefered jump...I use 0.025" for 22 cal, 0.015" for 6mm and 0.010" to touching for 7mm and up for all new rifles I build as a starting point for load development. Sometimes it works, sometimes the rifle has other ideas.
Finding what seating depth your rifle likes for a specific bullet is part of the crap shoot of reloading.
I always recommend 6mmBR, Saubier and various Varminting forums for new comers and doing online searches. There is tons of information out there to be gleaned on ALL aspects of reloading.
Luck