Barrel shortening

[Luftgewehr100]

... shorten a Hw100 barrel please..

Wouldn't it be easier to buy a 31 cm barrel of the carbine and sell your old longer barrel?
Your barrel has to be shortened, threaded and recrowned. I can't imagine this is cheap...
And who guarantees that precision is superb like before?

With a shorter barrel Your HW100 will be less powerful, You need to adjust power, You have
less shots and it will be louder...

Perhaps an overbarrel silencer will help if available in UK which makes Your gun a bit shorter.

[Benelli B76]

Rather have it shortened from the breach end or you will lose the choke.

Baz