this p90 is in 21 st century, not in 23rd :> weapons change...
Also Fallout universe does not equal ours after A-bomb drops...I think weapon balance needs to be done very carefully and such rush changes could only mess it up.
weapons were developed by HK in 20 or 21 century, not later than 2077
first thing real p90 is made by FN(Belgium, Fabrique Nationale) it has 50 rounds of 5,7 ammo...however in Fallout universe we have non-existing HK(German, Heckler & Koch) version, then it is shooting 10mm ammo and having 24 rounds in a clip
http://en.wikipedia.org/wiki/FN_P90...It has a capacity of 50 rounds and it is clear plastic...
The P90 in Fallout is a H&K and not a FN. So these are two different weapons. Wikipedia is not a valid source in this case. :p
In Fallout Tactics it was the FN P90, yes. But this is not Fallout Tactics online. :p