Receiver rail guide.

[Sieger]

Originally Posted by MFC

Try putting a piece of freezer or electical tape on the back of the frame where the rear toggle hits. If ammo and springs are in spec, it should leave a dent in the tape. If the tape is mutilated, either the spring is too weak or the ammo is too hot.

Hi:

Excellent advice!! This is low tech, but has been a standard test for years.

One additional thing. When there is breach block slap, you can really feel it in the web of your hand upon firing the pistol.

Sieger