IMR powder was formerly DuPont,  then later branded IMR, and now has been acquired by Hodgdon.

IMR powder was formerly DuPont, then later branded IMR, and now has been acquired by Hodgdon.

Loading Density

Various combinations of bullets and powder charges can be assembled to achieve the same velocity. Some are going to be more accurate than others. Various manuals will often indicate loads that gave the best accuracy in particular guns. This is usually the best place to start developing a load, although such a combination will not necessarily be the best performer in your gun.
Generally speaking, when selecting a powder there are a few rules of thumb worth following. Larger-capacity rifle cartridges, with heavy bullets, generally perform best with slow-burning powders. For best accuracy, a powder charge that fills the case with little or no air space tends to give better accuracy than a small charge that can shift position in the case. Shooters using reduced loads, particularly in rifles, get better results by tipping the barrel skyward before each shot to position the powder to the rear of the case.
Compressed loads should be approached with extreme caution for obvious reasons.
Approach Compressed loads with extreme caution.
This can also be achieved by using wads or wads plus fillers to fill up the space, but the results are usually not as good. A filler wad should never be placed over the powder with an air space between it and the bullet. The space must be filled entirely. If there is a space, the wad will come slamming against the base of the bullet with enough force to make a bulged ring in the case and often in the chamber of the gun!

Compressed Loads

Never compress powder in a cartridge case unless such a load is recommended in a reloading manual. Compressed loads should never be more than 10 percent above the case capacity. A compression of more than this often leads to lower than desired velocities. If the compression is excessive it can actually bulge the case or cause the case to stretch in the loading process, resulting in a cartridge that is oversize or too long and will jam the gun.

This article is an excerpt from ABCs of Reloading, 8th Edition. Click here to learn more and get your copy.

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