There is a little known repeating air pistol which used this type of loading system - the El Gamo R20. This is basically the El Gamo Falcon, which has the usual flip-over breech loading block, and alongside the barrel is a spring-fed magazine tube. Pics are here, courtesy of Spanish collector J. Perez : http://i135.photobucket.com/albums/q...psgmszwfvp.jpg
http://i135.photobucket.com/albums/q...ps4edellvc.jpg

The system is so simple, and I imagine almost infallible with ball ammo, that I don’t know why this pistol didn’t become better known. It would have been very easy to manufacture as it would only have required the magazine tube to be fixed on the side of a standard Falcon. However it must have had a very short production run and it is very rare. I have only ever come across two examples. If anyone owns one I would like to know how it performs. Even better, if it is available for sale or swap I would like to be first in the queue!