Picked up a great 220ST with the rounded rail.
Not really good for anything. Had thought about milling it flat.

Anyone do any early rail modifications?

I would prefer if SIG had decided to use a true mil-spec pic. rail, but even the SIG proprietary rail will work for accessories. I've used various WMLs on an assortment of SIGs and all have locked up tight and remained stable, until I removed them.

IIRC, over the years, one or two members have had the GG team either mill rails off completely or reprofiled them on a couple SIGs over the years.

If you do decide to tackle the project be sure and take some before/ after photos and let us know how the project goes.

Why not look for the compensator that fits that rail.
You would also need the longer barrel from the 220 Sport.