HW77 cocking issue?

[Gecko]

Stripped my 77 to fit one preload washer but after putting back together to cock the gun i have to pull the lever very hard for it to engage.
Looks like the latch is going far enough back.

Ive shimmed the front stock screws to rule out the cocking arm catching the screws.

Edit - looks like the preload washer is slightly larger then the OD of the spring could the piston be catching the preload washer?

[Gecko]

Ok stripped the gun and removed the preload washer and it cocks fine.

[bhodge]

Was the washer particularly thick..i.e. more than about 1mm?
What kind of power was the '77 putting out before you tried the extra washer??

[Gecko]

Its was doing 9.3 with exacts.
The washer i fitted was 3mm but there was also a 2mm washer so 5mm total.

[MattyBoy]

Washers must not be more than 20.6mm diameter

Hth
Matty

[Gwylan]

Washers must not be more than 20.6mm diameter

Hth
Matty

Why's that Matty? does the piston go so far back it fouls the preload washer?
I assume the OP isn't putting the washer behind the spring guide, that would muck things up.
other things that could cause reduced power are a damaged or tight piston seal, or leaking breech seal.

Gus