9mm RO Build

Living in Kaliforniastan I don't work on lots of RO pistols. I have a 9mm I'm getting ready to build and I saw something I'd never seen before. The frame rails have raised pads. Still have some typical RO vertical and horizontal play.
Has anyone else encountered the pads? I'd show a pic but my phone has been dropped one too many times and takes horrible pics.
Jon

Pads?  Where are they Jon? Top, sides?  Are they frequent/periodic so the slide rails ride on top without hitting the ends of the pads?

Don,
They are on top primarily and barely extend out to sides of rails. There are 4; two front and two rear on each side. I'd send a pic but phone sucks
Jon

Sounds like they're "sacrificial" fitting pads to allow a tight fit slide to frame at lock up.  The pads would be fitted to the slide groove.  These would allow a tight lockup and not impair functioning.

I wouldn't call them 'sacrificial'. They would offer less friction if slide was fully bearing on them, bit its not. Frame to slide fit is no better than typical 45 RO. Not much difference between lockup (in battery) or full recoil. By the way, any looseness in full recoil is typically because of gunsmith intentional fit not factory.

Interesting.  Cannot imagine why they did this.  I guess in theory if slide was fully bearing on the pads in lockup, one would only need to fit the pads to make a slide fit.  But I would think the pads might wear faster than full rail fitting.

When some  top pistolsmiths build pistols on already built pistols they weld up only a portion of the rails similar to this. So maybe SA is copying them?
Jon

Hmm, would that RO belong to someone that we both know?

I have a pair of them! They are both different but the same  Rails are different....both getting exact same comp but 1 is Kart and the other KKM. I need to compare serial numbers to see how close their birthdays are?