I bought a RCBS Uniflow from eBay it was listed as used. When I got it I took it apart to make sure there wasn't going to be any powder left over. I run through a hopper full of powder go to refill and noticed quite a bit of powder stuck in the barrel and at the bottom. I am guessing that it was actually new and RCBS's rust preventive was not wiped off. Should of just cleaned it while I had it off, but I guess I was just a little too excited to use it.

Would it be okay to still use the powder that I ran through it or would it be better to just cut my losses?

I bet it is fine.

Agree, would clean out what stuck but that covered the gunk for most of what fed through.

Of course if in doubt use it as fertilizer, clean out the equipment and start over with clean dry powder drop.

What they said. If any, the contaminated grains would all be gummed up in the works. Clean it up and drive on...;-)

Ok to use powder already dispensed.
One trick I found helpful, when the powder measure is all clean, it can build up some static and cause some powder to still stick in the hopper and spout.

Wipe the hopper, and all parts that make contact with powder, with a dryer sheet. You know, the same ones you put in the dryer with a load of wet clothes... Helps a lot!