Ah! Got it now, thanks for narrowing down my search too. I finally found mutli angle photos of the bt one and there really doesn't seem to be any option for using it with anything but rails from the way it's built.
Originally Posted by sQuidvision
If you have a tracer though (new one?) you should be able to mount the SA-17 mag directly.
old style pmi. the stick feed I built works fine, and the feed neck itself works great for cram-n-jam but a spring feed would be a nice option if for nothing but fancy points. A member here made one from a PT Xtreme clip and a spyder sight rail, but I'm not enthused about cutting up the body to make it work.
Edit again: Found the empire sniper ones for sale in one of my bookmarks. O.K. price too. I'll invest in one down the road.