Thank you
@BeemanHW100 - Stock is from Craftsman Vit in Ukraine. They are specialised in laminated stocks and bullpup conversion kits for Weihrauch, Air Arms and BSA mostly. Looks aside these are very ergonomical and well balanced. A real joy to handle. Highly recommended! Not sure how business is for them nowadays with the war and all. Sad.
The cylinder mount is not used for a bipod (although i guess you could hook one)

I use it to attach a flashlight or IR for nighttime. Picture was taken when i had the rifle configured for higher power 40fpe and was shooting slugs. It's a .22 btw. Even though it was a laser at the 100yds (those HW100 barrels are great for lightweight, soft-lead slugs) the shot cycle was very violent, silly loud muzzle report and poorest of shot counts - even with all the modifications i've done to the rifle (not much factory standard left).
Tuned her back down since then and added lightweight scope and tiny moderator. Sweet little shooter at a tad over 20fpe now. Lightweight, silent and as air efficient as can be (6 mags). Loves these fairly new .22 JTS Dead Center 18gr pellets. Edging out the JSB heavies.
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Thanks again for your interest. Be happy to see/hear about your and others HW100 adventures too.