I thought I said this up there - next time I go to the range, I'm going to use a rear bag; I have no other scope to try that's 1".
Since very little can be ascertained by 3-shot groups, moving up to 5-shot groups (or even 10-shot) will only yield more data; increasing group size will not confound the 'results' of 3-shot group testing, precisely because those 'results' are of dubious value to begin with, statistically. So, this technically doesn't qualify as changing a variable. Just gives more reliable results and thus conclusions.
Only doing any of this with the Tikka, at the moment. If the results are way better than initially observed, I may try the same things (or a subset of those things) on the Montana. Of course, firing more shots per group isn't going to improve the results of group size, but rather will yield more reliable conclusions. E.g., if the 5-shot group is smaller than the 3-shot group, then it is more probable that whatever variable was changed in that test had a positive impact on accuracy. If the 5-shot group is the same as the 3-shot group, then it's more probable that the 3-shot group, in that particular instance, happened to reflect the actual accuracy of the rifle. If the 5-shot group is larger than the 3-shot group, then it's more probable that the 5-shot group is reflective of the rifle's accuracy potential.
I think I see what 16Bore was saying a little more clearly, on re-reading his comment, namely, that I did all this without being 'sure' about the scope or rest. 1) I don't have immediately available another 1" tubed scope (nor rings to fit a 30mm scope on a Tikka), and I assumed that it would be a relatively low probability risk that a brand new scope would be performing poorly, vs. a rifle with the reputation of the Kimber (i.e., at times it has been spotty with regards to accuracy), and 2) I am sure about the rest, in that I've shot every other rifle I've owned - and I've owned other rifles that would reliably shoot groups (with my hand loads) a fraction of the size of the groups these two rifles have shot on average - in the same manner as described throughout this series of experiments, without it causing an issue.
That doesn't mean I'm closed to 1) the optic being the culprit (as I posted up there, that is one of the potential sources of the issue that I'd like to rule out), nor to 2) using a rear bag to eliminate movement (again, as posted previously, I will use a rear bag next time).
