RE: bought new remington .700 BDL
"Rimfire and Centerfire"?
"Prime"ary (pardon the pun) difference between the two is this: All self-contained cartridges require some kind of "kicker" - called a "primer" - to cause the main powder charge to burn.
Yes, contrary to popular fiction, explosives and powder don't "blow up", they just burn faster than your eye can see.
This primer (I won't bore you with chemistry) requires only a sharp blow, like that which comes from the firing pin, to cause it to ignite, in turn causing the main powder charge to ignite, pressure inside the case and chamber to rise, and the bullet to be "spit" down the barrel since it's the path of least resistance for this chemical combustion process you've just started to relieve itself of this high pressure.
In a "rimfire" cartridge, the primer is located in the rim of the cartridge. In a "centerfire" cartridge, you'll note a little round circle on the head of the cartridge. Currently, the only rimfire cartridges you'll find are the .22 family (short, long, long rifle, magnum) and a couple new .17s (the .17 Mach 2 and .17 Hornady Magnum. Used to be a 5mm Remington Magnum rimfire, as well as (way back) some .44s. Scarce today. On the other hand, EVERY big game cartridge you'll find today falls into the "centerfire" category, as well as handguns. Rimfire ammunition isn't feasible to reload. Centerfire ammunition certainly is feasible to reload (just pop the little primer with the dent in it out the way it went in and then plug a new one in).