Im guessing youve tried other brands of ammunition?
Im thinking your revolver has a issue with the hammer strut.
I remember there being an issue with H&R rimfire revolvers in general having a plastic mainspring shoe that bear's against the hammer is prone to breaking due to age and the stress of the hammer spring bearing aginst that ageing part that engages the hammer.
There is a steel replacement part that is supposed to fix that issue that others had use to replace the broken plastic ones, but those steel ones were for much older revolvers, H&R switched to plastic to cut production cost, if your lucky you may still be able to buy the plastic ones (now over 30 year old parts) and the steel ones have been already bought up.
You can find youtube videos on swapping out the hammer spring on H&R revolvers.
Depending on your particular revolver some have a frame mounted firing pin and some have a spur, some mainsprings are straight and some have a slight angle depending on that model but all the newer H&R rimfire revolvers had those plastic parts that are prone to failing.
https://www.gunpartscorp.com/products/276950A
https://www.gunpartscorp.com/products/276870A
Another place to try for parts is Jack First Gun Parts
Jack First Inc. 1201 Turbine Dr. Rapid City SD .57703
605-343-8481 Fax 605-343-9420 they dont do on-line ordering call them up with your brand, model # and serial number to get the correct production run type as older models had changes to the part over time. (These folks had hard to find High Standard parts that Numrich didnt have in stock)
https://www.northwestfirearms.com/t...s.com/threads/mainspring-with-steel-guide-for-old-h-r-929-22lr-revolver.222222/
https://thefiringline.com/forums/showthread.php?t=475645
http://m.leeroysramblings.com/fixing_DIY_gunsmith_job.html
https://youtu.be/tpV-7ytS8Nc
