Question About Barrel Shapes In Some Ruger Semiautos

This has been on my mind for a long time whenever I've seen it, and now again with my new LC9s:

Why does Ruger machine a "valley" or a "pinch" into the front of some of its barrels? I'm sure there's a reason for it, but I'm showing my ignorance by saying I have no idea what it is. Do other manufacturers do it? Why or why not?

Update: After pondering it for a few minutes, the only thing I can come up with is that maybe they engineer a "weak point" into the barrel that would allow it to fail less catastrophically, more "controllably" in the event of a squib load followed by a live round. But it's not every model, so I'm still perplexed.

You can see what I'm talking about with this picture.

If you notice that your new pistol doesn't have a barrel bushing like a 1911A1. That ''valley or pinch'' as you call it is for the barrel to lock up to the slide when your firearm is in battery.

loaded round said:

If you notice that your new pistol doesn't have a barrel bushing like a 1911A1. That ''valley or pinch'' as you call it is for the barrel to lock up to the slide when your firearm is in battery.

Click to expand...

And, it is relieved just aft of the muzzle so that when the barrel tips down during the cycling process, it won't bind up in the slide. 8)

5of7 said:

loaded round said:

If you notice that your new pistol doesn't have a barrel bushing like a 1911A1. That ''valley or pinch'' as you call it is for the barrel to lock up to the slide when your firearm is in battery.

Click to expand...

And, it is relieved just aft of the muzzle so that when the barrel tips down during the cycling process, it won't bind up in the slide. 8)

Click to expand...

Thank you both very much, those explanations make entirely too much sense for me to have surmised by myself. :lol: :roll:

I'm sitting here thinking: "Are they making the barrel flex to tune the pressure pulse? Does it have something to do with resonance?" Duh. Thanks again.