Is it possible to determine velocity based on actual bullet drop?

[CShooter92]

I don't have easy access to a chrono but am wanting to develop the DOPE for a new rifle. Is it possible to fully develop an ACCURATE dope out to 1000 or further without having an accurate muzzle velocity? And maybe my bigger question is there a way to calculate muzzle velocity based on your actual drops encountered in the field?

I was thinking of doing something like this:

Estimate muzzle velocity based on load data from manuals and this forum
Input into JBM or similar calculator
That will give me an estimated dope to run out my rifle
Shoot and measure actual dope for each yardage compared to calculator
Adjust calculated drops based on actual drops
??? Reverse calculate velocity based on those drops???? Not sure how to do this step.

 

[diverdon]

If you are using the JBM calculator, and you have your drops at 1000y. I think all you would have to do is use different numbers for your MV until the program showed you the drops you are seeing, and that is your mv. That of course assumes you have good data on your bullet.

 

[CShooter92]

Ok... so basically just a trial and error method with JBM to get it to match drop based on muzzle velocity assuming all other conditions are correct. In theory, should muzzle velocity change based on atmospheric conditions?

 

[diverdon]

The only thing that should matter is the temp, and how much that matters depends on the powder. Usually not more than half a fps per degree, so unless you are looking at large swings in temp you would not have to worry about it. Of course you want to set the correct density altitude for the day you established your drop. Humidity you can just set to 50%

 

[Keyrock]

I did something similar at the train up for the Rifles Only Brawl.

I had a new barrel and no dope for it. I had a notion of the velocity but I know that can change with a new barrel.

I was using the Geoballistics app and by using the muzzle velocity truing at 300 yards to establish velocity, I was able to get out to 1,000 and make some final truing at that distance.

Once I was confident that I needed 8.2 mils to get to 1,000 with a -650 DA, I knew I was done and the app would have sufficient information to generate a solution from there.

I think any decent app would have a muzzle truing feature, but I like Geoballistics.

The one word of caution is that this process is very dependent on the shooter being consistent. If a round went over the top of the target, it doesn’t always mean the dope is off and that you should be tweaking numbers.

 

[shipereyes445]

You may find this helpful.

http://en.wikipedia.org/wiki/External_ballistics

"The deceleration due to drag that a projectile with mass m, velocity v, and diameter d will experience is proportional to 1/BC, 1/m, v² and d²" "Due to the practical inability to know in advance and compensate for all the variables of flight, no software simulation, however advanced, will yield predictions that will always perfectly match real world trajectories. It is however possible to obtain predictions that are very close to actual flight behaviour." I am sure you can work out a workable approximation for your game though. There is also a balistic calculator here.

Reference https://www.physicsforums.com/threads/calculating-bullet-velocity-reduction-over-time.652727/

 

[Sparky7674]

Agreed^^^^ probably the best way to build accurate dope. The bullet is one part that doesn't lie. Even if you had the muzzle velocity. You essentially still have to go through the same process to true the information you have entered.