In an earlier life, I was involved in some projects to look at alternative calibers for the military use (as opposed to 9mm, 5.56, 7.62). The biggest problem is (without getting into a lot of milspeak) getting around/working within the DOD procurement system. The second biggest hurdle is getting our NATO allies to go along with any changes. Whether we want to admit it or not, we have to play nice with others due to treaties and defense agreements with other nations. As I understand it, some of your Spec Ops folks have more leeway in this regard than the rest of the DOD. Doubt that an alternative caliber is being looked at very seriously, since we crammed the 5.56 down their throats in the late ‘60s.
Several years ago (prior to end of the Cold War) H&K did some work with caseless ammo in the G 11. Interesting stuff, but a lot of problems with the application as I would imagine there is with the polymer cases. I know nothing about polymer cased ammo, other than what is in the article, but I think JASmith hit the nail on the head...heat...
Another consideration would be durability. MilSpec ammo gets the crap beat out of it before it gets fired. Not being a material engineer, but I wonder how well the polymer ammo would hold up to that abuse.
Several years ago (prior to end of the Cold War) H&K did some work with caseless ammo in the G 11. Interesting stuff, but a lot of problems with the application as I would imagine there is with the polymer cases. I know nothing about polymer cased ammo, other than what is in the article, but I think JASmith hit the nail on the head...heat...
Another consideration would be durability. MilSpec ammo gets the crap beat out of it before it gets fired. Not being a material engineer, but I wonder how well the polymer ammo would hold up to that abuse.