Thanks for the explanation Dthomas and from your post I believe you to be one of the graduage level professionals.
If I have a new rifle and I am doing load development, why would I want the SD from the whole population or how would that help narrow down a powder? Say I am trying out 3 different powders, wouldn't I want the SD only from each individual powder?
Your question is worded slightly confusing.
I'm assuming you are planning on using STDEV.P and using N as the denominator? If so, you are using the entire "population" of the ammo you loaded. You are saying that is all the ammo that you will ever produce like that. Which is fine. If that is the only ammo you're ever going to produce with those specs and the process you used, then yes, you'll want to use N as the denominator and move on.
However, if you will be making more ammo of any of those test batches, then it is now a sample of a larger population. "Random" doesn't mean that you have all the ammo produced and such. Random sample just means "equal probability of being chosen." So yes, there is an argument to be made that if you only make 5 rounds, they can't be a "random sample" since you don't have a larger population to choose from. However, this is just going to be philosophical and semantical in nature. As if you produce those 5 rounds the exact same way you would 1,000 rounds.....then those 5 rounds have an "equal probability" of being a sample properly representing the population of ammo you have yet to create.
And then you need to properly compare the date. Which means, if you use STDEV.S for one, you use it for all. So, if there's a possibility or assurance that you will be making more ammo with one of the recipes, then whichever recipe you choose is now a sample. So, you'd want to use STDEV.S to compare it to the others. Otherwise it would not be a fair comparison.
Now, if you are only testing a certain aspect of ammo, such as powder, and the next batch you are going to change something about all the ammunition, then it's likely more appropriate to use STDEV.P
As always, the actual answer isn't black and white. You can find reasons to use both S and P functions with ammunition. And claiming that any chronograph is "wrong" for picking one over the other is likely an incorrect statement.
IMO, they should show both calculations and let the end user decide. Or the end user should just use a chrono to get velocity for each shot and then calculate the SD they desire to use.
up to be notified when it comes in that's how I got mine when I receive the notification I ordered it immediately!
