Extreme Spread, Standard Deviation

With proven cast bullet loads for the cartridge, I pretty much do what RicinYakima does.  I shoot 5 foulers then 20 shots for group with no time limit but shooting fast enough to keep the fouling "soft".  That's usually a shot every 2 - 3 minutes.  That 20 shot group will tell if that load is good in that rifle.  If that group is acceptable then, depending on how acceptable, I might try another test of that same load with a test on each side with a .5 gr + and - difference.

If developing or attempting to "dial in" a load with a different powder unproven powder or with a different bullet, then you can shoot an awful lot of rounds.  I prefer to go with a couple, maybe three, known performing powder(?) if testing a new bullet.  Probably will expend 50 to 100 rounds with a powder "dialing in" a load. 

Actually, I am trying a new powder in my .308W match rifle.  I have 50 rounds (5 different loads) loaded up in 1/2 gr incremental charges to chronograph and shoot for group. If the groups and SD/ES are acceptable i will then do the 25 round test of what appears to be the best one.

Bottom line answer is I will expend maybe about 100 rounds with a proven load testing a new rifle/barrel.  However, many times known proven loads will perform as good as it gets and thus only the 25 rounds with each load would be expended testing.  If working/dialing up a load perhaps 150 - 200 or less rounds may be expended depending on the performance.    

Frankly, I am not one to shoot 2, 3 or 5 shots out of a new barrel and then jump into a competition with it.  

I have seen numerous BR competitors at a BR matches (jacketed bullet BR matches) put a new barrel on, shoot 2 - 3 shots then shoot the match.  Never saw a winner do that but have heard many moan and groan at the "wailing wall" (score board) because the new barrel shot "lousy"...... 

LMG