A Word about my process. There are two goals in mind. One is to find the charge that will have the lease change in velocity between rounds that are plus or minus .2gr for the target charge. The other goal is to find the charge that is tuned to the rifle such that the groups are very tight. These two goals do not necessarily include each other.
I loaded up 50 rounds of 6.5 Creedmoor using H100V - a hybrid powder that is very tolerant of temperature. I discovered that the IMR4350 that I have been using for decades will increase 70 ft/sec for every subsequent round, gaining hundreds of feet per second over a 10 shot group with my 270 hunting rifle. I never knew that because I never had it over a chronograph before. Also, I did not shoot many rounds at a time because most hunts had one shot kills and so as long as the first shot is completely predictable, all is well I guess. Having said that, when my IMR4350 is shot up, I will be doing a similar exercise with both my 270 and 300 mag -
Here is the data I collected on my workup for the 6.5 Creedmoor:
(10) 5 shot groups
|6.5 Creedmoor||143g Hornaday||H100V powder||CCI200||New Hornaday Brass|
From the table, 42 grains has only 14 fps spread and a standard deviation of 5.19 - really excellent!!
One thing that always surprised me was how you could have more powder and the bullet can move slower - here are graphs to show the results
here are the targets showing groupings at 100 yards
I got lucky on this one the best consistency is also the best tuned for the barrel - for the most part ...