I have 1 std 10rd mag and a 10 round with extension making it a 12 rd. Also comes with a new 10rd spring and another extension. Both aics SA.
Asking 120 shipped
Just make sure when u measure, u clean the the the throat perfect. Maybe use some break clean and compressed air to blow it out. Go slow and take your time. Try and get a bottle of thin cutting oil also.
There is a set screw under the cheek peice, remove it and the spring. Set the wheel in, drop the ball, spring then set screw. I think there are some vids online but I can take a pic if u need me to.
I wouldn't think that would be to large to safely fire but the brass would probably have issues in another chamber. Also I wouldn't trust any caliper to .0005. If u need that precise of a measurement you need a micrometer.