Way back in the early 1990s when we first introduced the Seattle Slug, we offered it in both a "regular" and a "concealment" model. The "regular" model came out first, and we offered the "concealment" model as a custom product. As it happens, the "regular" model worked pretty well concealed, so the "concealment" model remained a custom-order-only proposition. With the rise of USPSA Carry Optics (which forbids any extension of the frame) we've got more and more people asking us for the concealment model -- so we decided to make them "for real." The Snail complies with USPSA's requirements, and offers shooters a way to get maximum weight into the gun -- and smooth out your reloads considerably by filling in the void inside the grip. (Which tends to snag the rim of the top-most cartridge in the magazine.) You'll get a little under 3 ounces of weight out of the modification, which is enough to lower the center of gravity and smooth out the way the gun behaves -- particularly while speed reloading. This model fits the Glock Gen 2 and Gen 3 frames. There is some variation from Gen to Gen, and from serial number to serial number, so take care to shim up or shave down the slug so you get a gentle press-fit. (Robin likes using a layer of electrician's tape to snug up a loose-fitting Slug/Snail.)