To help date yours, the closest SN for one on my list is 1086xx which shipped in 6/22. Yours is probably close to that date. The ".32 W.C.F." caliber stamping on the barrel was changed to ".32-20" about that time. You may or may not be aware that .32-20 ammunition, while still made, is not the easiest to locate, and it can be quite expensive. Most of those who use .32-20 rifles and revolvers much will load their own to circumvent the logistics difficulties. Back in the day, the M&P in .32-20 was not nearly as popular in .32-20 as was the same revolver in .38 Special. S&W ceased .32-20 revolver production in the late 1920s. S&W's .32-20 SNs stopped around 145,000 (they were numbered in a separate series from those M&Ps in .38 Special).
At one time, there was a high-velocity .32-20 loading made for use in rifles only, which is not recommended for use in revolvers. You are highly unlikely to find any of that on dealers' shelves. It now is purely a collector's item as it has not been manufactured for over 50 years. Any newly manufactured .32-20 ammo you find today will be perfectly OK to use in your revolver, even if the box says "Rifle" on it.