User blog comment:Sentry 616/Weapon Gushing/@comment-27144409-20190719213529

I've got one that's fairly young, and somewhat sadly, unadopted. The XM-307\XM-312.

First, if you're curious why I listed two designations, it's because one can be converted into another in under two minutes. The 307 is a 25mm belt-fed grenade launcher/autocannon. The 312 is a .50 cal

For the 307, part of the idea is to be able to kill a room, trench, foxhole, etc. at long range, but with minimal collateral damage. As opposed to bringing down a wall or even an entire building to drop a sniper, which can happen when soldiers get angry at being sniped. There is a smaller single operatoor weapon built on roughly the same principle, but it's also still limited to the experimental designation after some problems.

The 312 was intended to be a replacement for the M2, complimenting the 307, especially since they shared enough parts that you could convert one to the other.

They're surpisingly light and stable. Fire a few rounds and a cup of water will stay on the whole time.