Power factors

[Ganderite]

In my loading logbook I note the Power Factor of most of the loads I test since it allows me to compare different calibers, different weight bullets and different velocities on a somewhat common scale.

I use IMR 7625 for much of my plinker and practice ammo (meters well in my thrower - flake powders do not).

It ocurred to me that power comes from the powder, so the same powder charge should give similar power with differrent calibers and different weight bullets, right?

Here is what I found with 5 grains of powder in different calibers:

38Spl 148gr WC PF 151 (shot in a 357 - too hot for 38)


40S&W 180 SWC PF145

44Spl 240gr SWC PF152


I was surprised at how similar the power factors are.

 

[domyalex]

Power factor is basically momentum (m*v).
IF the heavier bullet is accelerated to a inversely proportional velocity, then yes, the pf should be roughly the same.
The assumption here is that the same quantity of powder will generate the same energy, which might not be true due to different cases/pressures/burn rates/et al.

 

[V29189***]

power is not fully gained/produced by powder/propellant alone.

if I push you over, or push a car over, I generate the same force, but with vastly different results.

Thus - similar cartridge, different masses in bullet, will have different PF - different velocities.
(bullet weight x velocity fps) /1000 = PF

try some basic math, and then experiment reloading.

180gr x 1050fps/1000 = 189PF
160gr x 1150fps/1000 = 184PF
240gr x 880 fps/1000 = 211PF


enjoy - shoot lots

 

[Ganderite]

Guys, I know what a power factor is. I was just pointing out that when i used the same powder charge in 3 different calibers and 3 differnt weight bullets, the PF came out about the same.

Not an earth shattering issue, just something I noticed that might have some logic. Power comes from powder.

 

[domyalex]

Guys, I know what a power factor is. I was just pointing out that when i used the same powder charge in 3 different calibers and 3 differnt weight bullets, the PF came out about the same.

Not an earth shattering issue, just something I noticed that might have some logic. Power comes from powder.

Again, yes, you probably get similar pf because, in this particular cases, the same amount of powder is producing roughly the same amount of energy, but that doesn't always hold.

Put the 5 grains in a 30-06 case behind a 180gr bullet and the results will probably be different.