An additional complicating factor is the type of bullet used, that is lead or jacketed. If a cast or swaged lead bullet is used, the barrel friction is less than a jacketed bullet of the same mass. By this I mean that a cast lead 158 grain semi wadcutter (abbreviated as LSWC) will have less bullet friction in the barrel than a semi-jacketed soft point 158 grain bullet. Accordingly, the lead bullet will have a different powder charge required for a given muzzle velocity than the jacketed bullet.

In addition, the powder (whose weight is also specified in grains) will have a different charge weight for a given bullet type and weight depending upon the burning rate or speed of the powder, and the barrel length used. For example, a slower burning rate powder can be charged to a higher weight in a longer barrel, since it will continue to burn and increase gas volume as the bullet moves down the barrel. A faster powder will burn up completely in a shorter barrel, and if a charge comparable to that of the slower powder is used, excessive pressures with potential damage to the firearm may result. In the shorter barrel, a lesser charge of slower powder will be used, otherwise excessive flash and blast will be observed as the incompletely burned powder burns as it leaves the muzzle.

The science of bullet acceleration, powder gas evolution and chamber pressures vs. muzzle velocity is called interior ballistics, since it occurs before the bullet enters free flight outside the firearm's muzzle. All of these factors, as well as bullet mass, bullet friction, environmental temperature, primer brisance, case volume and powder position within the case affect the final velocity, muzzle energy and recoil energy.

Since few of us have the equipment, resources, and time to determine these factors, we use the various reloading manuals on the market. The authors, editors and publishers of these manuals have done the grunt work for us, and as a result, have made handloading a relatively safe hobby.