I have not seen the Rackmaster variation of the Winchester slugs. However, a few years back, I did some informal testing of a bunch of different Foster type slugs in 3 different Remington 870's and a 1100 20 ga., all with smoothbore slug barrels. The regular 2 3/4 inch Super X slugs turned out to be the most accurate, overall, of them all. As I did this a while back, that may not be the case today, I don't know. I'd say give the Rackmaster a try and see how it performs in your gun.