HW 77 power to accuracy ratio

[bozzer]

If it is second hand it could be a 25mm or 26mm diameter piston.

The 26mm pistons made a tad more power.

If it's 25mm 0.177 then it will be very sweet at about 13fp. The 26mm 0.177 would probably be half a foot pound higher.

In 0.22 the old 25mm were very sweet at about 14-15fp. You could push them a couple of fp higher.

So if 25mm 0.177 then not that much more than 12fp.

Remember that that amount of additional power is going to make not a lot of difference regarding useful range.

So if a 12 fp rifle is going to be useful to about 40 yards for 'responsible' hunting ... then at 13.5fp it's going to be about that same max range. It won't give you another 20 yards.

Worth noting because it may be easy for you to buy a UK 12fp tuning kit from Tinbum etc ( other tuning kits available ) and with a polish and washers that kit gives you around 12 or a tad over ( * see note ). If that's the case and it shoots well at that then there's no point messing around chasing an extra 1 or 2fp because it will give you no advantage.

*Note ... The 12fp kits are made to achieve around 11 - 12fp but polishing internals, fitment of piston seal and spacer washers used could make the rifle just over 12fp with some pellets, so the user ( restricted by UK law ... I understand the OP isn't ) has to check the power and set accordingly.