A little more info needed? Gun wash containers? what did they contain? what type of skip is it?
I work within the explosive/chemical health & safety area...
These are the clues.
I can't see a problem with it, so long as the barrels are empty.
What about taking them to a scrap yard?
That's where you're wrong, as it depends on if they’ve been correctly decontaminated thus why I asked what are “gun wash containers” are they a jet washing container? A rifle container? Other? Plus what type of chemical was stored within this container, is it explosive? Highly flammable? Etc…
All this will depend upon how they will need to be disposed of. You cannot simply just place them into a skip for general waste unless you want prosecuting.
Very few scrap yards will take businessbusiness waste. Not only that very few will take hazardous waste as it costs them more to dispose of.