I would say that it might cause some bore wear, depending on the material of the flechette's fins. They do look like they are lead or some other soft alloy (compared to the piercing body of the flechette). If so, even if it does "rattle" a bit as it traverses the barrel, as long as it is a "soft" metal, I don't think it would harm a standard bore/barrel. But for the most part, the sabot is what is contacting the bore, and the fins "appear" to have a smaller diameter than the case mouth. I would imagine it would be hard as hell to find, and a cursory search found someone who is allegedly selling it for [url=http://www.ammo-one.com/XM216Flechette.html]nearly $40 per round[/url]. That makes .50 BMG cheap by comparison.