Larger calibres were the most popular for double rifles of that period.

I am interested particularly in the Webley output of Doubles and more specifically in 450/400-- but if the 450,470, etc, calibers had twice the numbers made then more may be encountered at a ?"better" price(guess I'm dreamin').

Even if they made more guns in those calibres, it would not make them less expensive. In fact just the opposite, due to the fact that the two you mentioned are the most popular.

Webley built alot of doubles for the trade especially for the "bought in" side of things. I think output was around 14,000 to 15,000 guns prior to WW1.

There’s a couple of different actions to note, the PHV-1 and the A&WC. The quick tell is the dolls head which on the PHV-1 is shaped like a spade, The A&WC is shaped like a spade but with the point clipped off and the lever round indexed to it. Both are considered screw grips in the “trade”, however, Webley refered to one as a screw grip and one as a 3rd bite, the PHV-1 being the later. The A&WC long bar with intercepting sears is possibly the best built action for the rigors of double rifles. Webley built for many firms, the gun makers gunmaker.