Is there a reason why you suggest the Kurz version than the regular barrel length?
Better handling. A pellet has usually accelerated to its peak velocity within 12" to 13", so the rest is just unnecessary friction.
As we talked else where, do you think .22 is better than the .177 for rabbits and pigeon shooting in UK?
That's a can of worms but I still firmly believe in the larger calibre for pest control work. However, if you restrict yourself to headshots only then the .177" calibre would be better as it has a relatively flatter trajectory. However, if someone like me were in your place then I would go for a FAC .22 as I wouldn't always take head shots. Back of the head, spine, neck and chest shots ( from the side or front) will do the job. FAC .177" tends to zip through at upto 20-25 yards which often does not result in instant death. All this has been taken from the Airgun BBS, where this subject has been discussed exhaustively.
Finally,can a non FAC HW77 be tuned to FAC power for a later day use?
Without any problem. Would recommend a V-Mach / Venom DIY FAC kit. Quote your serial number as Weihrauch increased the ID of their cylinders by 1 mm after a certain serial number. This number can be seen at
www.airgunbuyer.com in the V-Mach section.
http://www.airgunbuyer.com/Showproducts ... ing%20Kits
Mack The Knife
P.S.: The serial number is 1446049 and over. These (HW97 and HW77 / K) have the larger cylinder.