Range Report Consistency of velocity on a chrono

[khw9mm]

I know a chrono is useful for load development and see what kinds of velocity and consistency of it am I getting.

But if I reload all my rounds the same exact way, what would cause one from getting inconsistent velocities??

This topic may have been discussed before so I apologize in advance...

 

[The Mechanic]

Re: Consistency of velocity on a chrono

You "think" you reload them exactly the same but there are so many variables to account for you will NEVER get there. Not to mention the errors in chrono's

 

[khw9mm]

Re: Consistency of velocity on a chrono

I get what you mean, what are some of the less obvious variables though? So that I can be more aware of it while reloading.

 

[The Mechanic]

Re: Consistency of velocity on a chrono

Case volume, neck tension, powder variance from lot to lot, runout, warm chamber cook, env from day to day, etc.

 

[skep_tic1]

Re: Consistency of velocity on a chrono

Respectfully.... You will never get your rounds to have the exact same velocity. Use a chrono to work the load. Change powders if needed, tweak the load all you can. When you get a recipe that holds single digit averages for the extreme spread then you will have arrived.
When I do load development I pick a goal for velocity. Once I get close enough to realize that my goal velocity is achievable. I tweak and experiment with powders until I obtain the best consistency I can reach. Normally I can hold an extreme spread of 10fps or less. But anything can effect this... even the weather. How would I be able to do this without a chronograph.

 

[CoryT]

Re: Consistency of velocity on a chrono

If you believe that the ES is ACTUALLY in single digits, I'm afraid I have bad news for you. The chronograph you are using is +/- 1% ON ANY GIVEN SHOT, which is a lot more that 1 digit. If you want a reasonable expectation of an average velocity, you'll need to have 40 or so rounds tested and then use the SD, which is a far more meaningful number than ES. 98% of your shots will be within 3 SD's of the mean, and that's about the best you can hope for with any load. I'd be pretty happy with an SD of 10-12fps, and that's even inside the chrono's actual margin of error.

 

[skep_tic1]

Re: Consistency of velocity on a chrono

SD may indeed be what I am referring to. However I do figure the mean based off dozens of shots fired.