After having a fiddle with it, I can now see why the shroud was fitted, it was to allow for the fitting of a silencer, the shroud did not fit tight to the end of the barrel or in this case the thread in the end of the barrel, there was a 20mm gap between them, this then allowed the silencer to be fitted without fouling the air cylinder but the silencer had to be taken off when the cylinder needed filling.
The thread in the end of the barrel looks like it may have a ring of solder around it, I don't want to attempt to take it off in case I bugger the thread up and possibly the end of the barrel, I wanted to remove the shroud to see if it would have any effect on the groupings as they were not great, now that I have removed it they have certainly tightened up.
HW 77 V glide kit by Steve Pope
8-40x56 Custom Shop.
HW 101. Big Nikko. Ginb FT Stock.
Webley Omega, Gas Ram.
Rohm Twinmaster Trainer.
Red Dot Sight.