A reader emailed in the below photo which was taken by a friend of his on a visit to the Russian Central Army Museum at Moscow. On display is a Mosin Nagant rifle with a huge suppressor (labeled ’6′). On the far left is a submachine gun which appears to have a rifle grenade attachment. Can anyone identify the gun?

UPDATE: Its not a suppressor, but a grenade launcher. Thanks to the Mosin aficionados who pointed this out in the comments.

[ Many thanks to Tarkan for emailing me the photo. ]