28.0 grains falls below the minimum loads listed by Hornady for both bullet weights you asked about; although not so much for the 300 grain weight as the 240. I've always shied away from loading charges greater than 10% below listed min.

2400 or WC820 (available from www.gibrass.com) would be a better choice for the type load you are looking for in my opinion. Good neck tension on the bullets should give you a clean enough burn on the powder.

I used to really like 30.0gr of H110 and the 300gr XTP or 325gr cast bullet. It was my do all 454 load. It chronoed 1550fps out of my 8 3/8s Raging bull.