Out thats a simple OLD warning used by everyone that has built any ammunition for shotguns in the last 100 years. Damascus steel is GORGEOUS steel and only seen in custom knives built in the last 75 years or so. It is essentially steel cable that is pounded into flat " steel" and shaped. Like I said its very pretty metal that has a " grain" appearance much like wood, but has very weak pressure limits. Again NOT a concern of yours. The " twisted steel" is very similar and again is a very old metal working technique that produced " non solid" tubes of metal. I think you are making a very common mistake in the assumption that " twisted steel" is equal or similar to a rifles barrel and the two are totally unrelated. A truely rifled barrel or rifled choke tube is an entirely different animal.

I can only imagine that by being fired in a non rifled barrel/tube perhaps the sabot wouldnt properly form a gascheck and seal the bullet properly for propulsion down the bore which could possibly result in a plugged barrel. But if that were the case you wouldnt be able to fire it in a gun which only had a rifled choke tube. Perhaps more appropriately is that the slugmaker is telling you that you likely wont get very good accuracy without some sort of rifling to impart a spin on the projectile for stablilization. I guess theoretically you COULD fire those slugs in a gun with a very " loose" smoothbore that was tightly choked and the sabot could loose velocity as a result of not sealing properly (again the gascheck scenario and perhaps a possibility in a backbored barrel which I doubt you have in a common singleshot!) and the sabot could become lodged in the barrel as a result. I think you would be fine safety wise, just not very accurate!

Good luck and what the heck, get you a rifled tube!
RA