velocity variations

[daniellybbert]

Im not sure how to word this but here it goes
how much of a variation in velocities (of a bullet) can there be before the groupings change
I was shooting some loads today and the shots that were within 5fps cut the same holes but more than 15 fps there was a considerable diffrence
so Im wondering what your tolarence level is

I think Im going to buy a balance scale and double weigh all my loads

 

[rkaine]

I've been told and read that when you develop a load, try to look for a SD (standard deviation) that is 10FPS or less. Distance to the target is going to make a difference as well, a small variation at 100 will be magnified at 600 and 1000.

 

[Obtunded]

In the first place, few Chronographs are that accurate anyway, but the differences of a few FPS are so small that a change of POI is really the result of the myriad of other variables that occur between shots. Barmoetric pressure, differing air densities, humidity, thermal radiation (Mirage) changing barrel dimensions with heat, the bullet and and the shooter.

Use a ballistic program on-line to plot the theoretical down-range change in POI based on 10 FPS differences in MV.

 

[Mystic Precision]

Unless you have a wide or multi screen chronie like an Oehler, the error in the machine is larger then the numbers you are trying to analyse. A Chronie has a 1/2% error in their reading. That is +/-15fps at 3000fps.

I found that testing at 200 to 300yds resolved any issues I had with load and stringing.

Jerry