ACD, you've got some misconceptions about factory and reloading stated/quoted muzzle velocities. But then most people who've been reloading for over 40 years do too.
If several people were to take a given round of ammunition, be it factory or reload, then shoot a few dozen of them in several different barrels, there would easily be a 150 fps spread in muzzle velocities. Here's a list of things that make this happen:
* Powder lots each have slightly different burn rates. Powder companies usually blend two or more powder lots to get a batch of powder with burn rates within specs for the powder type. And each blended lot sold to the public will have slightly different burn rates; same charge weight from two lots may have a 30 fps difference in muzzle velocity.
* Case neck tension will vary depending on how much the case neck was sized and how deep the bullet's seated; tighter means higher muzzle velocity. Crimping in the bullet adds to case neck tension.
* The bullet's jump distance to the rifling has a small effect on muzzle velocity and pressure; the more the bullet moves before entering the rifling the lower peak pressure and muzzle velocity will be.
* Firing pin spring strength impacts primer detonation characteristics; weak ones result in lower muzzle velocities.
* Chamber, bore and groove diameters vary across different makes and even within makes of barrels. Larger bore and groove diameters, even by only a few ten thousandths of an inch, result in lower muzzle velocity. Rifle factories using precision test barrels to test pressure and muzzle velocity are made to exact specifications; they're expensive. They typically produce higher muzzle velocities than their regular production barrels with a wider specification range.
* Barrel length effects muzzle velocity. A 30 inch barrel will shoot the same load 100 to 200 fps faster than a 20 inch one depending on the bore dimensions and particular cartridge and its components.
* Depending on how the rifle's held, muzzle velocity will vary. Two people holding and shooting the same rifle with the same ammo can easily produce up to a 100 fps difference in average muzzle velocity. And the same person shooting a given rifle and load will get higher muzzle velocities shooting from the prone postion than from standing/offhand.
* And finally, if you chronograph factory ammo in your rifle, it will probably be 50 to 100 fps slower that what the factory lists it at. If this happens, one or more of the above issues resulting in lower muzzle velocities will be in effect.
So.........
Loading ammo's not an exact process. Military arsenals know this and they adjust charge weight of each lot of powder to get muzzle velocity and peak pressure withing specs. Handloaders can do the same thing if they've got the right tools (machine rest to hold the rifle for shot-to-shot holding repeatability, chronographs and pressure gages). And many folks reload ammo to much higher pressures and muzzle velocities than factory ammo 'cause they get away with it and don't care or know about very short case life and dangerously high pressures.
Whatever your target is, it doesn't care if it's hit with a bullet traveling 100 fps slower than what some sales and marketing group says it will. If it does, it's powerful and strong enough that shooting it with anything won't phase it at all and it's probably going to get even with you before you can shoot it again.