[Raider65]

Here are some little known firearms (at least to me, just found them a few months ago) that could maybe fit within this timeline.

A "caseless" pistol. Second version had 48 round magazine.
http://translate.google.com/translat...v.html&act=url

An AK prototype with multi-shot grenade launcher.
http://militaryclub.narod.ru/war/pers.htm

http://русская-сила.рф/imgg.shtml?im...gu/80002-1.jpg

http://www.allmilitaryweapons.com/20...ult-rifle.html

Edit:

A "light" .50 rifle for those big beasties! Limiting factor only has effective engagement range of 100m.
http://world.guns.ru/assault/rus/ash...t-rifle-e.html
http://en.wikipedia.org/wiki/ASh-12.7
On the third pic, cool .50 handgun prototype. Also ASh-12 has a 3 shot rotary grenade launcher underbarrel attachment and attachable suppressor.
http://www.thefirearmblog.com/blog/2...bullpup-rifle/

Or any of these weapons would be cool.
http://www.tulatskib.ru/HTML_a/sgv_prod_a.html

Edit 2:

Pic of more prototype Russian guns that are really interesting and cool looking.
http://www.forgottenweapons.com/so-m...o-little-time/

Edit 3:

Some links to more Russian prototype / experimental firearms.
http://img156.imageshack.us/img156/7391/pribor3bhy1.jpg
http://img145.imageshack.us/img145/7...ppergunjr2.jpg
http://img141.imageshack.us/img141/1...pergun2cs2.jpg
http://www.militaryimages.net/photop...v_TKB-011M.JPG
http://www.militaryimages.net/photop...32/TKB-022.JPG
http://pookieweb.dyndns.org:61129/Gr...ps/TKB-022.jpg
http://pookieweb.dyndns.org:61129/Gr...ps/TKB-408.jpg
http://www.militaryimages.net/photop...31/Bullpup.JPG

Edit 4:

http://www.warrelics.eu/forum/firear...el-made-26790/

http://parallaxscurioandrelicfirearm...v#.Uhc3Y7nn-Uk
http://i65.photobucket.com/albums/h2...chmentaspx.jpg

http://www.gunandgame.com/forums/pow...lt-rifles.html

Edit 5:
I hope at some time they allow us to find a fully stocked "lost" Armory that hasn't been looted (like the D6 in Metro) with modern (for the time period) weapons and also filled with some experimental / prototype firearms such as the AO-63.

http://images1.wikia.nocookie.net/__...3/3c/Ao-63.jpg
http://www.imfdb.org/images/thumb/1/...pion_AO-63.jpg