I will add a fix for the item splitting issue next release. Most servers run a stacks plugin which handles it, but I should have a native way to handle it for those that don't.
Regarding the assault rifle issue; the new rifles are completely new items, and not skins applied to the existing assault rifle item.
The default assault rifle's shortname is "rifle.ak", where as the abyss rifle is called "rifle.ak.diver" and the ice ak is called "rifle.ak.ice".
Since these item's aren't skinnable, they aren't supported.