There's a MAX amount of pressure that the bullet/primer/powder can meet, and NEVER exceed. The mfg's have to juggle things around to stay below this standard!! Changeing even the brands of primers can change the load, so everything has to be checked, and rechecked!!

Look on the box of ammo you bought, there's a lot number on it. It's usually on the flap, and it's on every box sold. That number changes every time something changes in the load they use. SO, if you buy Remington 30-06, 180 grain, every time ANYTHING changes when Rem. is loading them, that lot number also changes.

As was said above, there's many brands and burning rates of powder. Each brand and size of primer has it's own charge to do it's job, ect.. ect...

Drilling Man