Try e-gunaparts.com
"My pistol is .40 caliber." "We were fortunate to find a manager of his caliber."
It will usually be marked somewhere on the barrel.
No. It would requite a larger barrel and then you would have to find a bigger clip to hold the larger pellets. The larger clip would require that the gun be considerably modified. It's not worth it.
Impossible to tell from just the sn. if you found the serial number, you will be able to find the caliber of the pistol somewhere carved in the metal.
most any large gun store will have them.
Try e-gunparts.com
Provide DETAILED DESCRIPTION OF ALL MARKINGS.
You will need to take it to a gunsmith to find out.
We have them. gunshop@nctv.com
The company that made it or the dealer that sold it to you can find out what kind of pistol and know the calibur.
Call S&W with the sn and they will tell you.
any gun or sporting store