What causes peening and rounding of locking lugs?

[Candiru]

I was checking my Hi-Powers' locking lugs for signs of wear tonight when it occurred to me that I don't know the sort of gun behavior that causes damage to the locking lugs in Browning pattern pistols.

Reasoning suggests that the barrel disconnecting from the slide while there's still pressure in the chamber will mean that during disconnect the slide will be accelerating rearward due to cartridge pressure, thereby exerting force against the lugs that can cause damage. The solution to this would be recoil and main springs strong enough to retard the action to the point that the slide and barrel disengage only after the bullet has left the barrel. In this scenario, peening or rounding would occur on the front (toward the muzzle) of the barrel lugs and the back of the slide lugs. Theoretically, the reverse could occur in guns where the slide was allowed to slam forward without chambering a round.

Reason suggests all of the above, but I've been wrong before, and I could be missing a bevy of other possibilities that I'd like to know about. I love Hi-Powers and 1911s and want mine to last long enough to share this love with my grandchildren. Maybe this thread can be opened up as a discussion of maintenance practices that keep our Browning pattern pistols running happily.

 

[1911Tuner]

Rounded Lugs

Hi Candiru,

Could be that it's trying to unlock early, while pressure is still nailing the lugs together. Could also be that the vertical impact surface in the frame is too far forward and stopping the barrel before it's completely disengaged from the slide. Lower barrel lug located too far rearward will do that too. In the 1911,
a long link will do it, and a short link will keep the barrel from unlocking completely...or unlock it too early...so the dimensions of your lower lug and unlocking cam could be an issue.

Try a quick test:

Flip the gun upside down and hand-cycle it. If the lug/camming ramp is out of spec, you'll probably feel a slight hitch about a quarter-inch out of battery.
The slide may even stop dead and refuse to cycle further until the gun is right-side up.

Check the vertical impact surface in the frame and the rear face of the lower lug for signs of impact or hard contact too.