I use a nice little hinton of taunton boxlock for clays. Its nothing special, just the usual british boxlock ejector. I have been told by plenty of people that its unsuitable for clays as its too light. But to me if the gun fits you properly (which it does) and you use the light 1oz or less clay loads (which i do) then being pounded by recoil need not be an issue.

I have also heard the old chestnut that old side by sides simply can't stand up to the constant firing of shells at clays. My response to that is have a look online at youtube or the like and watch a video of a driven pheasant or grouse shoot, those guns never stop firing, and most of the quality old guns over a hundred years old are still going strong.