99% of the time, you can tell a Lewis and Crass apart by counting the screws on either side of the frame, a Crass has 5, and a Lewis shows 4, since the sear pin is hidden under the wood, on the Lewis model. The exception, is if either has ejectors, that adds a screw on each. The sure way, is if you can open the gun, and see if the rib extension is pierced. I Lewis has a rib extension bite, a Crass does not.