Here's an interesting point....... In the STEN, the angle of presentation of the round was 7 degrees - according to the EMER that I've just looked at. This angle was ensured BY THE MAGAZINE. IN THE STERLING, THE ANGLE OF PRESENTATION OF THE ROUND IN THE MAGAZINE WAS SQUARE to the magazine. Have a look for yourself. The actual angle of presentation to the breech face was caused by the complete magazine housing being angled at 7 degrees. Therefore when you insert the magazine, by design, the top round is presented exactly at 7 degrees - nose pointing to the centre of the chamber opening.
Clever lad that George Patchett. Discussed over a boozy lunch with James Edmiston yesterday!