Please help identify a 2 inch rifle launcher cup part 1

[breakeyp]

This launcher is 10 1/2 inches long. The bore is 2" diameter and 7 1/2 " deep. The wing nut brass ring rotates to expose holes which vent gas in varying amounts thus setting the projectile range. Attachment is a straight slot with rotating ring to trap the front sight. A long lee barrel fits but cannot lock in place. There are no markings.

Attachment 96802Attachment 96803

Information

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[Melanie_Daniels]

Mosin Nagant M.91?

[Gil Boyd]

To me it looks like a reworked Dyakonov grenade launcher, but if there are any markings they will be on the neck, I may be wrong but I think I can make out a 6 there in amongst the crud!!.