SGL;
Yes I agree here that mat'l specs are litterally a part of the "Design". I was however generally speaking of the mechanical design features. This is where I say there is only extremely small improvments (if any) in the "design" of a 21. Its design improvement is its metalurgy. The hinge is a good one, but they just found a slightly different way of doing it, nothing really innovative. J W Livingston had a patent for a hinge pin back in 1880 which was used on John Nichol's hammer guns which accomplished the same purpose & of course D M Lefever & F R Smith's 1882 patent for the ball & socket joint are legendary.
Not sure about Purdey's assesments, generally speaking the milder the steel the faster you can cut it. May be some other factors involved.
The Clabrough & Sauer do not have compensation period. The top lever comes to a positive stop at center & the bolts just slide home. There is just the barest minimum of clearence for them to slide & though I wasn't around when they were built all indications are they have virtually the same clearence today as they had over 100 yrs ago. When you think about it, the friction on these bolts is essentially Nil, so they don't seem to wear. Likewise on the rear lump, as it is not Pulled into a frictional condition by a forend spring it doesn't wear to any extent either. Even if the hinge wears to some extent the gun can go "Off-Face" only to the extent of the clearence on that rear lump.
Winchester very wisely chose to use modern steels which were available to them upon introduction of the 21 & on that factor built a "Deserved" reputation of a solid & durable gun. They did not however make any great "Innovations" in gun design with it. There are litterally hundreds of makes out there built to a superior design, but mostly of lesser mat'ls, though most of these have given great service & satsfaction to their owners, many for a long time & for lot's of shooting.
