USSR
Member
@USSR, which do you think is the greater variable:
-hand loads with Sierra 150gr GameKings on top of IMR4895, measured to +/-0.1gr accuracy, using same 1x brass and primers, which through 9-shot groups of 4 different charges have shown the most consistency
or
-a completely unknown rifle (barrel, action, stock, scope mount, scope)
I am experienced at troubleshooting other types of problems, but unfortunately not at troubleshooting inconsistent groups. So given my experience with this rifle so far, I would expect the scope and/or mount and the shooter to now be the greatest variables. I am not opposed to buying a box of match grade ammo, I just want to do my best to eliminate the most likely problem first.
Assuming you have first checked you scope mounts for not being loose and tried a different scope that is known to be good, then the next step I would take is going with a load with a known history (Federal Gold Medal Match), so as to develop a baseline and eliminate your reloads as a factor.
USSR, Sorry to bust your bubble, but ALL factory ammo, including "match grade", is still more prone to inconsistencies than a careful hand-loader. The OP hand-loads and seems to know what he is doing in that respect. Unless that factory hand weighs each and every charge (and no Fed Match Grade is NOT), and every charge comes from the same lot, (Again Fed Match Grade is not), then there is no possible way to be as consistent as a careful hand-loader. Plain and simple. So that "base line" is not really a base line at all. A careful hand-loader would be able to provide a much more consistent load value than ANY mass produced ammo.
Hmm, if all that is necessary to develop extremely accurate ammo is consistency and being careful, then all handloads would be accurate and there would be no need for load development work. You can develop various handloads, all carefully and consistently put together using different powders, charge weights, COAL's, primers, etc., and you will have varying degrees of accuracy. As previously stated "If the rifle doesn't group well with FGMM, something is wrong with the rifle". It's all about eliminating a variable; his handloads.
Don