I’ve been reloading for my rifles since my college days long ago. I’ve never loaded for my revolvers and have decided to learn. At some point in the late 1990s I bought powder ( 4227 & blue dot) and have never opened the cans. These have been stored inside for 20+ years. Am I good to use this powder or should I just start over with new powder?

Ive read that the powder has a subtle change in color and a distictive change in smell when it goes bad. I've not seen it first hand. I'd guess that unopened containers reasonably stored would last a lot longer thsn 20 years.

Unless it has been stored at high temperatures it is probably fine.
If it smells like acetone, that is a good sign.
If it has a rusty red color discard it by spreading thinly on a lawn or garden. It is a good source of nitrogen.

Thanks for the input! I appreciate it.

When my father died, I inherited half of his powder stash. One of the 8 lb cans he had was some old Hercules 2400 that had been in his reloading room as long as I could remember, which was at least 40 years. My brother and I split the 3 lbs or so left in it. Using my dad's load data in his guns, I got the same velocity that he had listed for loads that were at least 30 years old. Curious, I duplicated the load data with new Alliant 2400, and got velocity averages that were nearly exactly the same. His reloading room was 58-64 degrees year-round. I have seen zero issues with any of the powders I inherited from him. I just mention the 2400 because I know it was at least 40 years old.

I'm currently using some Alcan AL-5 from the early 70's at the "youngest" and more likely the mid to later 60's with no ill affects. I've used even older surplus powder like Hodgdon sold as H4831 many times. I have both powders mentioned by the OP on hand and all are much older than his as well as being opened.

As mentioned, if it is not acrid smelling and/or no red stain/dust, use it without worry.

I'm using up some 2400, Unique and Blue Dot that's at least 25 years old, and I don't remember how much older. Results over chronograph are almost identical to what they were in the past. Cans were were used and closed normally. They don't miss a beat. Same with some old rifle powders. They've been relocated a couple of times but always indoors.

I am still using some surplus 4831 that was bought in bulk in the 70s by my dad and his buddies and was old pull-down powder when they bought it. Likely WW2 Vintage. I have run it over a chronograph and it is very similar to recent lots of modern H4831. Very consistent with low SDs as well. My dad also gave me some Bullseye he got from an older neighbor that was bought in the 70s new and it also worked great. Powder stored well has a very long shelf life.

I use some H110 from a 3 LB coffee can given to me by a friend. I seems to work as any can of H110. I fill the hopper and close it up. I keep it in a room set at 40% humidity and between 55 and 65* temp. I use some 4064 bought years before Varget came out and it works nicely in several calibers that I load. I have rarely if ever found powder that went bad here. I would use it as fertilizer as above. Be Well, Rustyzipper.

If it smells off and has red dust on it then it becomes fertilizer.

In some cases, powder stored in plastic canisters may react with the plastic. Had some that formed "clumps".
I keep most of my inactive or seldom used powder in metal canisters.
Sometimes will use the plastic if I know it is being used up quickly.
Smell and appearance are critical.