Figureing fps of a projectile with points of impact at 50yards and 25 yards

[cramerklontz]

Homework Statement

So. I'm a muzzleloader hunter. If my rifle has a sight height of .85 inches. and groups at 25yards are 1.5 inches above 0 and groups at 50 yards are 2.5 inches above 0. The bullet I'm using has a ballistic coefficient of .205. The bullet weight is 240 grains. Is it possible to calculate this with only 2 points of impact? What is the feet per second?

Homework Equations

I have no clue

The Attempt at a Solution

I was plugging numbers into a ballistic calculator and couldn't get a good result.

This information is important because a fps that is too high will lead to poor bullet performance on the target.

 

[LawrenceC]

Is the bullet still rising at 50 yards or is it falling by then? Also if the ballistic coefficient is .205, what is the drag coefficient? I have a program that will solve this problem but I need drag coefficient. The program I have will also compute the drag coefficient but it is for modern bullets. Drag coefficients are functions of bullet speed. Let me know and I'll try to help.

 

[LawrenceC]

You can purchase a chronograph for around $70. I have one.

 

[cramerklontz]

The bullet is a 240grain hornady xtp in .44 cal. I was hoping to not have to buy a chronograph, but I do want one. And yes I believe the bullet is still rising at 50. from what I've read on the internet its going anywhere from 1600 to 2200 fps

 

[LawrenceC]

That bullet is a hollow point that is not pointed. I do not have drag coefficients for that. I've been playing around with my program input using spitzer point drag data. When I come close to matching your two data points, my velocity is too low. This is because my drag coefficient splines are for spitzer points which have a lower coefficient. I don't have the curve fits for your bullet profile.