The Delta does have a removable mag, but parts are incredibly difficult to get a hold of. I just finished parting one out two weeks ago and the demand for parts was so bad that I sold everything down to the trigger shoe in less than a day.
PBN5.com used to have all kinds of parts for the Delta, but their website has taken a dump. The only place left that I know of where you can get a magazine is here
. Expensive, but they've apparently got them.
That being said, I actually find that reloading with ten round tubes is actually faster and more efficient than using magazines. That, and those little aluminum catches on the body are delicate and relatively easy to break. Putting a key chain on the endcap of the magazine so you can pull it and keep it on your finger while you're reloading will make your life easier. I keep a dump pouch open and just drop my empty tubes and caps in there.