Originally Posted by
sagela
"Because they have to touch the barrel at the same point. "
Nope. The bullets have different ogives. One .224 bullet tapers upward from the tip to groove diameter quicker than another bullet of the same weight.
You're already aware of magazine restrictions on C.O.A.L. Another potential restriction is the old rule of thumb, "seat the bullet to at least 1/3 the diameter of the bullet."
A long ogive and a boattail mean there's very little length of bullet at which it is really .224" in diameter - thus not much for the grooves to grab. This, in turn, reduces
drag in the bore which effects pressure. If some other thing, like magazine limitations, require deep seating, powder capacity can be reduced or a compressed load is required.
That's why most reloading data are now based on individual bullets rather than generic descriptions like "69gr FMJ."
Fun game.
Cncmachinist 
