April 19, 2013
When a 1911 pistol is fired, the slide and barrel move rearward for a short distance until the barrel link pulls the barrel down, unlocking it from the slide as the slide proceeds rearward to pick up another round.
The upper rear portion of the barrel bottom lug impacts the vertical surface forward of the barrel seat on the frame known among gunsmiths as the "bow tie" due to its shape. The pictures of this well-used Springfield clearly show the impact surfaces of the frame and barrel lugs mating correctly.
If the lugs impact the vertical surface of the frame below the "bow tie," they will be stressed and may eventually shear off. The frame may be incorrectly machined.
This problem can be corrected with a long center cutting end mill deepening the frame relief cut or by carefully removing a small amount of material from the lower rear of the lugs. A situation may also occur where barrel movement is stopped by the curved horizontal area forward of the frame feed ramp. Incorrect recoil surface fit is not a common problem but it's something to look for when cleaning your pistol.