I have pellets and powder that I have not used for about 3-4 years. It has been kept cool and dried. How long will it stay effective?

More than 4 years if it was stored right. Not sure about the pellets though. They seem to absorb moisture more than the powder.

Thanks. I live in Utah and its pretty dry most of the year.

I have dehydrated pellets in my food dehydrator and they worked great even though old , so if moisture is a possibility just dehydrate them .

I have some jugs of Triple Seven that are getting real old. Some of the unfired jugs are pushing three years. The main thing is keep the powder dry. If you open the jug and you see clumping, you might have some problems.

Last week,i had wondered the same thing! I called Hodgdon powder company and ask that question. A fellow named Cody talked to me and said " As long as it is kept dry,it will stay good the same as black powder."
I bought a pound of it,i can't remember how long ago,but it has been years! I've had it stored in a dry place. I am going to use it this week to shoot an inline 50 cal and some sabots,for my son.
I guess i will find out?

You'd have to chrono new powder, and the old powder to know for sure if it lost power. Just going bang isn't a good test.

The main thing I would look out for is the pellets they do NOT seal out the moisture the jugs of granular do if the are still sealed or closed tight.

I agree. I've never tried pellets, but i've seen the containers. If I shot pellets i'd put them in a ziplock baggy when they were new.

Just like my lunch.

Here's a great trick for preserving ANY powders or pellets.
You'll need a "FOOD SAVER" or other vacuum packing machine, but just put your powder or pellets in a roomy sleeve, and suck the air out and seal her up. No way any ambient moisture can get in.

Food Saver machines are awesome for storing more than just foods or meat for a loooooong time. Just found a packet of Oryx backstraps in the back of freezer from 2009. No freezer burn & still delicious!
Also a half used box of Pyrodex pellets from 2003. Took em out & fired em all. They worked perfectly... just like the Oryx steaks.