The largest container available for sale to the general public that I have seen is 8 pounds. A friend of mine now states that he has a ~25 pound can of RedDot that he's had for ~30 years. He described it as a large cylindrical metal can with metal lid like on the old Hercules Bullseye 8 ounce containers.

Did the powder companies once sell these large amounts of canister grade powder to handloaders?
If so, what other size increments were there? Did the US government in some way set a maximum size, such as a ICC trucking regulation?

In the late 60's I bought direct from Hodgdon a 50lb keg (cardboard) of WWII surplus 4831 for something like $40 add in American rifleman.

The more you bought the cheaper it was, I still have about 2 lbs of it left.

I don't think the Red Dot was in a 25 lb can but 16 lbs was the rule.

Don't know if there is a size limit on powder

Powders are still available in 25-pound containers. However, since UPS, FedEx and the other shippers have decided it is "unsafe" to ship containers with more than 8-pounds, they must be picked-up at the manufacturer or distributor.

You can't get them to ship a 25-pound container, but they will ship fifty 1-pound containers, thirteen 4-pound containers or seven 8-pound containers in one box.

Turns out it is a 16 pound can, not 25. Although he said it was ~40 years old...still good though!

Hey Steve. Liked that last bit, go figure!

20 lb kegs used to be common for newly-manufactured rifle powders (the 16 and 12 pounders were similar in size, but were lighter in weight due to the less dense nature of pistol and shotgun powders). To my knowledge, only surplus powders were ever distributed in containers larger than 20 lbs to handloaders.

Both shipping regulations (or "practices", as many "regulations" are simply internal policies of the various common carriers) and the changing nature of reloaders have made the larger powder containers impractical.

The largest container you can have shipped via UPS/FedEx is 8#. An individual or distributor can transport the 25# containers. The DOT regulated how much any individual vehicle can carry at 100 lbs before the classification must change to a class B explosive. Thus, many carriers don't want to bother with it anymore. If you do get your hands on a 25# keg be careful. It could be rated for fireworks rather than ammunition. Alliant/Hercules did have some 25# kegs of powder in the shotshell series. You currently have to have a class 06 FFL to get one. They require distributors to sign an agreement which prohibits them from selling these large containers to individual shooters.