Q. When trying blackpowder handloads in the Model 1884 Springfield Trapdoor rifle, what is acceptable regarding pressure?
A. Recommended maximum average pressure (MAP) for Trapdoors is considered to be 18,000 p.s.i., approximately what is produced by the original loading of 70 grains of blackpowder under a 405-grain lead bullet. No properly loaded cartridge with blackpowder should cause you any concern. However, it is vitally critical that all available powder space be utilized when loading.
To accomplish this requires at least a little “crush.” The easiest way of doing this is to measure the length of the bullet from base to crimp groove and subtract 1/16" from that measurement. This figure represents the remaining space from the powder charge to the mouth of the case when the powder is added.
Consistency is necessary for good accuracy, so it’s best to have a dipper or some means to replicate the charge. Seating the bullet will achieve the required crush.
