The Type 64 is a Japanese equivalent of FN-FAL, U.S. M-14, or H&K G-3: a Main Battle Rifle. The weird thing about it is that Stratos 4 and Kamichu take place in our days [Update: see comments]. But such rifles were obsolete for a very long time. Type 64 was replaced by Type 89 back in 1990s.
When Tsubasa and Mikaze shoot Type 64, it makes complete sense. Obsolete weapons move to training duties, where cadets get their hands on them.
Yurie-sama talks her way out of trouble.
But would the duplitious and paranoid Prime Minister send a bunch of guys with Type 64 in hand to do some important job? I highly doubt it.
I am begining to suspect that the image of Type 64's profile is imprinted into the psyche of an average Japanese as "the rifle", just like the AK-74's compensator is synonymous with a Russian soldier, and the M-16's carrying handle - with an American one.