I guess my question would be:
Why not? Is the gun going to blow up or something? Gentleman says it's got steel barrels, if the wall thickness is good and it's tight on face why shouldn't he shoot 2 3/4 non-magnum loads out of it? It's not like he said he wanted to use it for high volume doves in Argentina, he said he wanted to use it for coyotes. How many shells a year would that really cause to be fired? If the gun is up to snuff as far as condition and barrel thickness I'd say fire away.
Keith said he bought one for $100, I saw one at a little gun show this weekend for $300. They're not expensive, not what some folks would call a "fine gun", so why not use it and have fun?
And also why wouldn't buckshot be acceptable in it? I've seen orders for damascus Parkers where they were ordered specifically to fire "large buckshot" hence they were choked extra tight. It's lead, the barrel is steel, so the problem is what? He didn't ask if he could fire modern rifled slugs though it I don't believe.
I've got a Hopkins & Allen single shot I've killed a lot of squirrels with over the years using high brass 6's and it's never given me any trouble. I'd say load her up and give the coyotes Hell!
Destry
Blowing up would be thoughtful consideration of mine, yes. If you'd care to go to the source, try this:
http://www.alliantpowder.com/ You'll see that Bullseye powder is not listed as a shotgun powder because it's too fast burning. What you've done and gotten away with is not necessarily a good idea, or even necessarily safe on the next shot. That much Bullseye is not a recommendation, even in a modern shotgun. Please, everyone, GET YOUR SHOTGUN LOADS from established, tested and published sources. I don't want anyone injured, even smart alecs.