I have recently been having problems again with my MK2 sten. I had it rebuilt by John Andrewski and for about 7000 rounds it ran nearly flawlessly but now I'm having failure to eject malfunctions again. It usually happens on the last two or three rounds in the magazine.

I have 23 mags and four bolts and have tested all but to no avail. I have also replaced extractor springs and done some other things.

I have also checked the weight of my action spring and it's at 13# which seems about right.

It seems that the top round in the magazine may be bumping the case off the bolt face but I'm not certain. I have checked the feed angle on all of my magazines with the correct British gage and all of them are correct.

I'm not sure if this is a bolt velocity issue or something of that nature as when I hand cycle a case out of the chamber with a dummy round in the magazine it falls off in the receiver if I go slowly but lazily ejects out if I run it briskly. This gun has never had strong ejection by the way.

Have you got a slow mo camera? Figured out my Wilson was not ejecting consistently. Learned a lot. Most tubes were shorter than the originals by bout an inch as it was easier to make the parts kits into the tube. If you have a short tube, the recoil spring will need to be shorter to work properly. Is there tube exposed at the back of the magazine housing? I evened mine out with the housing and no more issues. Might check the ejector to see if it is dragging on the bolt. Start with the slow mo. This should give you  start on trouble shooting. If you google sten pics, you will see some of the tubes were trimmed back to the housing and others not..

Tag for the resolved issue