I'm pretty sure I had trouble with that...
I know there's a badly drilled hole in my overpriced black delrin ring, and I think the IBT was one of the tanks I wanted it for...
IBT has their OWN ring - and cheaper than other ones. It's made JUST for IBT - it's taller, and as you screw it on, it actually "pulls" the carto a little, and you end up super-snug - but it's got airholes. For an IBT, I'd get that one...