H&R 922, How can I research the date?

[dmacsilverado]

I am trying to research the manufacture date on a revolver I just purchased. The firearm is an H&R 922 .22 9 shot 6" barrel. Serial# 178628. The cylinder is stamped "PAT.1904 730". I know it is not worth much, however would still like to know the age.
If anyone has knowledge of this I would appreciate some help, thanks.
dmacsilverado