Home Forums Reloading Big Game Rifles Educate Me on Compressed Loads

To illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.

In a "normal" load with the bullet seated to allow about one 32nd of an inch gap between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period, and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.

Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start. Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps.

Bullet seated to touch the rifling -
When the bullet is seated to touch the rifling, as in the accompanying illustrations, it does not move when the pressure is low; and not having a good run at the rifling as did the other bullets, it takes greatly increased pressure to force it into the rifling. As the rapidly expanding gases now find less room than they should have at this time in their burning, the pressure rise under these conditions is both rapid and excessive. Velocity is high at 3650 fps - but at the expense of rather dangerous pressure. Many rifles deliver their best groups when bullets are seated just touching the rifling. Seating bullets thus can be done quite safely if the reloader will reduce his charge by a few grains. The lighter load will still produce the "normal" velocity without excessive pressure.