So I set out today with my new trusty Ruger Hawkeye 300 Win Mag. I had worked up some test loads to find what my new rifle was going to shoot best. The bullets that I had chosen were 180 grain Sierra Gameking spire point boat tails. I like these bullets for their design and the fact that they are one of the few 180 grain bullets that breaks .500 for ballistic Coef. I loaded these bullets with IMR 4831 and CCI 250 Large Rifle Magnum Primers. Here are the results. My question is what is going on with these groups?
This was the lightest load that I had loaded at 71.8 grains. decent group three shots at right at 3/4 of an inch
This is my second load at 72.4 grains. the group of three is 11/16 or just under 3/4 of an inch
Then this happens. Load threeat 73 grains opens way up top three shots measure 1 13/16 of an inch
This is load four at 73.5 grains. Here my group goes horizontal. The three shot pyramid is gone and is replaced with a horizontal string. What is going on?
Lastly load five at 74 grains. Even more dramatic horizontal spread. What makes a group change shape like this?
It is clear that my rifle likes a little lighter load. the 72.4 grain group that i shot will most likely be the one I load with. It is a medium to hot load but well under the max load in the sierra manual. None of these loads showed signs of pressure and would feel safe loading any of them, however the lighter two loads of the five yielded the best results. What is my rifle trying to tell me by the change in the group shape? Is there any way that i can use this data to further my progress in my load developement?