Just found out this for the BSA VC.......

The only airgun silencer you will ever need. This latest-generation silencer actually allows the shooter to match its internal specification to suit the calibre of the rifle. A supplied Allen key permits the removal of the end of the silencer, so that different size restrictors can be fitted, so increasing or decreasing the muzzle aperture according to calibre to maximise the reduction in noise-energy as the pellet leaves the moderator. This 'variable choke' facility turns a silencer into one of the most useful hunting accessories of all time.
The BSA VC Silencer is supplied with 2- interchangeable muzzle restrictors that should be matched to the calibre of the airgun it is to be fitted to. The black restrictor must be fitted to .177 (4.5mm) calibre airguns. The white restrictor must be fitted to .22 (5.5mm) calibre airguns. The silencer is supplied with the white restrictor pre-fitted. Please note both restrictors have oversize holes to allow for barrels that have non – concentric bores. If the silencer is to be used on .25 (6.35mm) calibre airguns, no restrictors are fitted. Access to the restrictor is gained by removing the restrictor screw from the Silencer end cap using the 8mm Allen key provided.

I didnt know this, im going to try to pick up the black .177 restrictors and give them a try?