Model 41 barrel modification?

Hello,

I recently acquired a second model 41 (ca. 1979) and finally got it out to the range this morning. Shoots like a dream--150 rounds through her without a hiccup. Anyway, cleaning it up this afternoon I noticed that the first 1/3 of an inch of the barrel (from the breech) seems to have been reamed ever so slightly. There's a visible ridge (of maybe 3/1000th of an inch) where the barrel resumes its standard diameter. Did the 41 ever come from the factory this way, or is this definitely a modification? 

I'm just curious--extremely happy with the pistol in any case.

Interesting, you might want to add some photos.  I have never seen this but some others might have.

I believe that is where the .22 cartridge sits in the breech.
I’ve noticed this (non-rifled) section in all my .22’s. I would have seen this as normal?