there definitely is an argument for both sides....having a majority of guns in one caliber is a very good idea. And having both of you carry one style of weapon is a very good idea, if you are in a fight and one of you runs out of ammo and the other is in a better position you can get the other the gun and continue the fight easily without trying to "figure out how it works" but it can also be done by time at the range. I always fire my husband's gun at the range, it's solid metal, it's too heavy for me to carry, (I have hip problems, I realize it's a great gun, but any extra weight is felt in my hips.) Wgoforth, I think it's him, has a great write-up about spouses carrying the same gun.
My thoughts on guns as investments are just that, my thoughts....alot of people speculate about the economy crashing....my thinking is, if it does, guns will become very, very valuable. Plus, heck, if there is a zombie apocolyse, who cares about gold, give me a gun
