Sean @ Everything Hunting has written a review on the Mossberg 100 ATR:

The Mossberg 100 ATR is one of the least expensive guns on the market. Coming with a price tag of about $298. What can you expect from the gun? I found the gun pretty accurate and light to carry at only 7 lbs. I bought the Realtree camo pattern with matte black barrel. I used the gun exclusively during the 2006 hunting season.

I have shot 3 deer (all head shots) with instant results at ranges of 15-85 yards. At the firing range I maintained accuracy consistent with a 3 1/2 inch bullseye at 100 yards. These results were sandbag gun rest only without a vise. I find the results to be consistent with my abilities. I feel that I may be able to bring the group closer with a better scope.

More here.