I'm with airfix. the inner tube is cheap, very thin, rubberry feeling, last great and after the first one their easy to do again.
I bought 1 tube and used it for my P99, my G17, my Kahr PM9, my AR15 handgrips and did a friends Glock and Ruger. And still had enough to cut in 1/4" strips for the Great English Mountain neighborhood rubber band war!!! Still have alot of Mommys mad at me for that one,hahahaha