As for the scale, I was printing the templates out in work ( which doesn't have any specialised image software) when I followed the instructions on BBC, I think the printing was enlarging the images to almost 'fit to page'. The way I got around it was opening the picture in picture viewer, but then I think I right clicked or selected 'edit' , this opened up a paint type program and when I printed from that program, it printed to the correct scale ( I hope).
As for pipe diameter, in the uk we use mm not inches and I couldn't find equivalent piping even after using an inch to mm convertor. So I am using 32mm abs waste pipe for the outer barrel and I think from memory 25 mm electrical conduit pipe for the inner barrel... Only problem is the 32 mm is going to be a tight fit and a slip of the drill could result in the receiver splitting...