Pressure or Force which is more important?
Many times we see firearms originally designed for black powder cartridges used for modern cartridges. The last one was a Ballard chambered in 22-3000. Normally the discussion on the subject gets no further than what the pressure was for the original design and what the pressure is of the modern cartridge. We do need to know the pressure of the cartridge but only to figure the reward force on the rifles bolt, breechblock or whatever. Please keep in mind that I am not considering the gas handling in the rifle or other important things that should be considered. The point of this is too show that there is a lot more involved than what the pressure of the cartridge is.
To figure the reward force
Area of a circle in square inches x pressure (if you have 25,000 PSI and the cartridge has 1 square-inch of surface area the reword force would be 25,000 lbs.) I use the outside base diameter, not the rim, to figure area. To do this properly I think the inside diameter at the base would be used. I don’t know for sure that a 45-70 is 25k or a 22-Hornet is 50K I just pulled some figures out of the air for this post.
Pi Radius-squared
Pi= 3.14
3.14 x Radius x Radius
45-70 at 25,000 PSI
Base diameter .500” so the Radius which is half of the diameter is .250”
3.14 x .250 x .250 x 25,000 = 4907 LBS.
.22-Hornet at 50,000 PSI
Base diameter .294” so the Radius which is half of the diameter is .147”
3.14 x .147 x .147 x 50,000= 3393 LBS
What this shows is that a cartridge with double the pressure can have less force on the action because of the cartridge size. This is the same reason why many double barrel shotguns can be converted safely to double rifles.
Please check my math, I once figured that a 275lb man (me) could hold one pound of gas pressure in a 24” vertical pipe by sitting on a piece of plexiglass while taking a picture of a obstruction in the pipe. I was wrong!
