Hi, mate.
They were an OK rifle in their day. Some of the early one's were a bit ropey, they seemed to be made of pig metal, the barrel's went slack in the jaws 'cos they were only held by a pin and the overall quality was iffy at best.
Later one's, mid 's on were much better, especially the 'S' version which had a walnut stock and far better build.
Like you said in your PM, they do share a good few parts with Airsporters of the same era, same trigger assy., same piston assy. and spring.
Good luck with it, mate.
Cheers.