in what conceivable situation would you ever need to make a head shot at 100 yards?
Hmmn...
How about any large city, suburb, or rural area going through the throes of major social upheaval (riots, looting, etc.)?
How about any LEO event involving a two-way engagement of armed felons where an exposed head is the only significant chunk of target?
In my experience, Macon, Georgia would support either paradigm nicely.
maconcop: I don't question the need, but I question both the weapon and a perceived need to modify it. With a magnifying optic, the Mini will do what needs to be done out to 100 yards (including a head shot). For 50-100 meter shots, the Mini-14 could get the job done with iron sights. Get a good zero at 100 and practice engaging the target that represents your worst case.
Any basic AR will do the same, but with better accuracy. For less money than required to gunsmith the Ruger into something that will deliver the mail, you could purchase just about any mid-grade M4gery that will do the same thing right off the rack. You don't actually need stainless, free floated, bull barrels to use a rifle for 100 yard shots. Any stock GI M16A1, A2, or M4 is perfectly capable of doing that shot with irons...assuming the shooter does his part. With a basic 4X scope it would become a much easier shot. I'm talking just using a basic Bushmaster, DPMS, S&W, etc.
If your heart is set on the Ruger (and there is a lot to like about that rifle), I'd not waste money on upgrading the Mini's barrel, but would recommend buying a quality scope instead.
If you
really need
precision accuracy at distances more than 150m, you are contemplating the wrong rifle.