Load Density
How completely the powder charge fills the case, expressed as a percentage, with high density near a full case generally giving more consistent ignition.
Load density is the ratio of the powder charge volume to the available case capacity, usually stated as a percentage of fill. A load that fills most or all of the case is high density, while one that leaves a lot of airspace under the bullet is low density. The figure depends on both the powder’s bulk and the volume of the particular case.
High load density is generally desirable because a nearly full case leaves little room for the powder to shift, which keeps powder position consistent from shot to shot and tends to produce steadier ignition and velocity. When the charge fills the case completely and the bullet packs it down, the result is a compressed charge. Loaders often favor powders that produce a high fill at the target velocity for exactly this consistency, while very low density loads can ignite unevenly and are watched more carefully.