I'm not sure which Chambers lock folks are talking about, but I can see where TOW is coming from.
After comparing the full size photos in their catalog I get the following dimensions:
L&R Queen Ann 1750 London style Length= 5.685, height from a line tangent to the bottom, to the pan= .975, distance from center of pan to sear arm= 2.900
Chambers English Fowler/Virginia Fowler style Length= 5.950, height from a line tangent to the bottom, to the pan= 1.00, distance from center of pan to sear arm= 3.120
Chambers Deluxe Siler lock Length= 5.370, height from a line tangent to the bottom, to the pan= .940, distance from center of pan to sear arm= 2.985
The height from a line tangent to the bottom, to the pan is the dimension from the face of the pan (where the frizzen rests) to a line which was drawn tangent to the front lockplate radius and to the rear lockplate radius.
This was done because the bottom of the lockplates are concave (bananna shaped).
I measured the three locks because the original post just said Chambers Lock. Was this refering to the Chambers Siler lock (which is smaller than the Queen Anne), or to the Chambers Virginia lock?
I ask because a lot of us build with the Siler locks, so that's what we think of when we talk about lock sizes.
These dimensions are probably close to the real locks but don't quote me. I mean, how close can someone measure a picture?
By the way for :m2c: I have had very good success with all of the L&R flintlocks I've built with.