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

1. Dec 1, 2011

### cramerklontz

1. The problem statement, all variables and given/known data

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?

2. Relevant equations
I have no clue

3. 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.

2. Dec 1, 2011

### 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.

3. Dec 1, 2011

### LawrenceC

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

4. Dec 1, 2011

### 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 belive the bullet is still rising at 50. from what i've read on the internet its going anywhere from 1600 to 2200 fps

5. Dec 1, 2011

### 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.