I'm sure this topic is as old as time itself. Searching didn't yield much.

Back strap grip reductions are often shown by filling in the void of the grip with epoxy and then grinding away plastic and epoxy until you get the desired grip geometry.  But epoxy can't be heat stippled.  Robar, for one, stated they don't use heat stippling so it's either mechanical or some kind of over molding process.  Maybe they don't use the epoxy fill method either? As to the grip reduction I've thought about cutting off the back strap hump entirely and gluing in a small block of black glass reinforced nylon and grinding it to shape on the grip. The nylon will take heat stippling.

If anyone does professional grade Glock frame mods, please PM me if you like and let me know how this should go for best results.  I understand if it's your trade and you don't want to share info.  I own a business and I know protecting industy info is important.  If anyone has done a good job on an amateur grip reduction mod, please feel free to post publically here. I'm doing my homework on this before I break out the tools.

I have reduced the hump on my 2 19's, 17, and 20 all with a heat gun. Be patient and heat it slowly and evenly or you will melt just the surface instead of making the whole rear strap pliable . I also put a few layers of painters tape on each side of an empty mag and insert it before heating just so I don't have to worry about  deforming the Magwell.

I thought I needed some reduction, so I just upgraded to a Gen 4 and without grips its a reduction over the standard Gen 3, that was enough for me....