DISCLAIMER: Stencollector has been kind enough to allow me to post and use his collection of material on building his SAS3 Sten, the actual gun used to get RCMP approval. The following is his work.

The mag well collar is manufactured it from 1/8" plate. Photo one shows the plate being bent around. The mandrel being used is an old roadwheel pin from a Brengun carrier, turned down to the outside diameter of the tube. The next photo shows it bent completely and before having the seam welded. The origionals were approx .105 thickness, although this varied between manufacturers. In another photo you can see where the outside of the tube is being turned to the correct thickness. The inside had to be bored slightly to provide a nice (but not loose) fit. The last photo shows the ejector port cut into it.

The port was accidently cut too long...had to weld a little metal back in place. The locator pin has already been drilled, and the magazine opening roughed into place.