Is there any files or listings available to show which models numbers are the same physical sizes. For example is a 5906 and 6906 the same physical size. I'm asking this because when looking for holsters not all S&W models are listed in the application charts.

Is there a breakdown of the model numbers in general, by family, barrel length, composition etc.

I believe the 5900 & 4000 series numbers have corresponding sizes. Ex.5906 comparative to 4006, would also be DAO models 5946 & 4046. Think there is a model 4013 equivalent to the 6906.

As for composition, the last digit of model# refers to material.
3=Alloy satin finish
4=Alloy blued finish
6=Stainless Steel

There are so many variations that no listing could be complete. Most of the 9/40 guns will work it the same but then you have both square and round trigger guards to deal with. The compact 40s' were made on both the 45 and 9mm frames, with and without light rails, etc, etc.