Calculating fps

brunobell

brunobell

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Does this assumption work? I'm assuming it's just a ratio when calculating fps. (which is used for estimating IPSC power factor)

Load data says: 147gr bullet, 3.9gr of powder = 895fps

Theoretically then for 4.2gr of powder the fps should be:

3.9-------895
------=------
4.2--------x

x = 963.8 fps

Right?
 
I don't think it is a 1 to 1 ratio. Many people using chronographs find that there is a point where adding powder starts giving less and less increase in velocity. They call it the point of diminishing returns.
 
Good to know, thanks for the replies. Is there any place/quick calculator where you can calculate intermediate velocities (roughly) without using a chrony?
 
No!

What happens when you hit maximum and your velocity spikes?

Get a reloading manual and test your theory. It is seriously flawed and not reliable.
 
Relying on your reloading manual(s) is the best thing to do.

There are ways to calculate velocities without a chrony, but it's for the most part a lost art, and you need to fire the ammunition to determine it.
The other solution for you would be getting a good ballistic program, such as Quickload or even Load-From-A-Disk, but you have to be aware that even with those programs, there is no way to precisely determine pressure / velocities.
But they cost more than a manual and anyways, the loads they produce will have to be double checked with a manual... or get a chrony... and still use your manual(s)...
 
"...calculate intermediate velocities..." Quit worrying about it. Accuracy is far more important.
"...good ballistic program..." I wouldn't pay much attention to them either. They're made by programmers, most of whom have never shot a real firearm. Far too many variables invloved for any computer program to be accurate anyway.
 
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