Re: Q about load development
I don't do anything special about cooling, but I take enough time to ensure the barrel never gets hot enough to be uncomfortable to the touch using the back of my palm. Because each of the first, second, third, etc., rounds of each group get fired roughly at about the same stage of barrel heating, then the overall effect is to shoot each group in a roughly similar barrel heating regime, eliminating unequal heating as a factor between groups.
If, for instance, I'm working with an overall charge somewhere around 25gr, the initial 2% increment equates to about .5gr. So charges would be arbitrarily, and for the sake of discussion, 25.0, 24.5, 24.0, etc. If the 24.5 increment comes out best, then I would bracket the charges at 24.7, 24.5, 24.3, etc., and see if any of these improves the grouping consistently.
Generally, I simply set the OAL at the beginning, averaging 5 dummy rounds point of OAL/rifling engagement and shortening that measurement by about .010". To me, the 'optimum' OAL engagement isn't determined by accuracy, but by consistently jumping (or not jumping) to the lands.
I don't seek ultimate accuracy, I seek acceptable accuracy. I define that as 1/2MOA at 100 benched, 1MAO at 200yd prone, and 2MOA at 1000yd prone.
When you test, you never, never, never, ever, ever, ever change more than one variable at a time. Otherwise you won't know which variable worked, didn't work, or cancelled another variable out.
Greg