Flare gun help

[Bruv]

I have a friend who has had this flare gun for quite some time. He wants to sell it now and he doesn't know too much about it, and I don't know anything about it other than it is an M5. Is that a standard, common typical, etc.? I would appreciate some help in some questions I have about it. Is it WWII or Korea era? What branch or personnel would have used it? What, from the pictures, would its approximate value be worth. He wants to sell it to fund another purchase, and I figured there are some people on here who would know all about it. I really appreciate the help I get on here as we don't get to see a lot of goods due to lack of shows out west here.
Dave

[Bruv]

more pics

[Bruv]

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[SIGNALMAN]

Hello, It is a WWII era, U.S. Martial flare pistol manufactured by Harrington & Richardson. It uses standard U.S. 10 ga. flares.

It is missing the lanyard ring, and I cannot see the locking latch spring. both will affect value. $100 - 150. $250 if all correct.

[Bruv]

Thank you very much for the information. The locking mechanism is springy feeling when unlatching it to fold the tube down, so I figure the spring must be there. The lanyard and attachment are gone. I appreciate your help.
Dave