I have used both alum oxide and silicon carbide. I think people get confused here. Silicon carbide can embed in the steel IF you were lapping with a harder lap. The grit will embed in the lead lap, not the steel. At least that is what I have found.
Yes, my worry is that it might still embed in a bad spot or maybe catch in a tool mark or such, but I haven't been able to find where that has happened yet. Haven't exactly lapped a thousand barrels yet either!!