Not all BrumBows do it; only about half mine did! I have some now fitted with a longstrokes piston where a new set of cutouts are made on the opposite side of the piston and the cocking slot was cut 0.5mm less deep than standard - no clicking! The increased stroke of 6mm means a less fussy tune gets excellent results in 0.177 calibre models. My original prototype (which I still have!) for long stroking had an increase of 8mm (the maximum achievable) but one required a longer cocking link (shotened Tommy!) and one lost the auto-safety feature! Steve Pope made all the mods for me and offers the +6mm stroked and glided piston as a tuning item now!
All mods I do to any model are rigorously investigated using dynamic techniques so I have voluminous records for recoil and vibration data collected over the last 8-10 years or so. Am busy trying to qunatify "awesome firing cycle" now which is proving far more challenging than just quanitying "gentle nudge in the shoulder" which is why I started all this!
I do agree with earlier post that the BrumBow is the finest medium weight barrel cocker on the planet! However, since now extinct, they will only get rarer!
As a quick addition; it is possible to re-shape the forward edge of the "mushroom" to reduce it's sharpness and decrease the friction at the forward end and, when done properly, I understand it eliminates the click too! Not as reversible as the disc though!
Oh; one could conceivably insert a piece of 0.5mm material in the cocking slot if one has the skill and patience!
Good luck all BrumBow fans.
atvb
David