swampman,
I use the same rings on my Weatherby Vanguard. They seem to work just fine. Pretty rugged rings.
How do you like your 100ATR? You are the first person I have heard of with one. Is it a good shooter? Any idea who is making them for Mossberg? I didn't care for the fit and finish myself, but if its a good shooter then the price is definitely right. I like the recessed muzzle crown it has. I'd love to hear how it performs for you.
SB