Best silencing option I tried for the HC.

Only about 4" long so doesn't compromise the Carbine length so much.
Plastic (hard nylon/delrin type material) construction so doesn't add much weight.

The Parker Hale worked well at attenuation as well but is longer and heavier.

I got my male-to-male adapter from Chambers
at around a fiver.

http://www.chambersgunmakers.co.uk/Silencers.htm

Pics of HC with SB and PH silencers

User gives his Plenum plug away.

Silencer thread

The Logun is a fine silencer but the springs ring with the recoil.
IMO it's more suited to a PCP.