Take a fired casing, use a pin punch to drive out the primer, then place it in the chamber. Pull the trigger and let the bolt go forward. If the extractor doesn't pick up the casing, your chamber is probably already too deep and reaming it won't do anything but make it deeper. As mentioned a couple of times, your problem MAY be in the snap caps you are using. They don't work well with guns that have fixed firing pins.
New Sten Gun owner questions.
Posted 10 July 2019 - 04:47 PM
I was finally able to find an original Sten barrel for
a reasonable price. The Sten now runs flawlessly.
If you have a sten parts.com barrel be aware the chambers
cut a little to tight. Now to get those other barrels working.
Posted 14 July 2019 - 11:40 PM
These snap caps have brass primers attached to a spring, so they'll move when struck by the firing pin.
(Amazon isn't the only source of these.)
My recoil spring (called "return spring" by the Brits) and the bell-shaped housing attached to it measure the same length as yours.
Alternatively, If you reload (or know someone who does) you can make your own dummy rounds with a spent primer.
Both my Uzi and Sten benefited from a bit of time in a lathe and emery paper applied to the breech. They were originally so rough that the cases dragged on their way in, slowing them down enough to preclude detonation. Now both 9mm's feed just fine.
If the new extractor/spring combo still isn't grabbing the case rim, check the channel on the bolt that they fit into. There may be a burr or some deformity keeping the extractor claw from grabbing. Posting a photo of the updated assembly would help the diagnosis.
Posted Yesterday, 12:50 AM
These photos may help.
In the first one, notice how close the extractor claw is to the firing pin. (Yeah I use a bronze bolt. Call me old-fashioned.) Yours shows a substantial gap.
The 2nd photo (the best I could do at night in my garage with an old phone) shows the extractor securing the rim of the 9mm case against the bolt face.