This is a launcher variant of the suppressor, which comes in both spigot (project 28-29) and a 37mm ID version with a grooved (not rifled) bore.
I cannot attest to the legality of the 37mm version, it is most certainly a destructive device, but can launch all of your flare stuff still.
the spigot version is as far as I know not illegal. I am not a lawyer, and this is not legal advice.
LBRY Tags: 3d2a; guncad; launcher; m1895; 37mm