Yes, I have tried them in my Encore .50 SS barrel. I tried the 250gr. and 300gr. (also come in 350gr.) using two T7 pellets (100gr). The 300gr. bullets shoot into 1.5 inch groups at 100 yds for me and are more accurate than the 250gr. in my Encore.
I actually used the above loads this past season and killed a button buck in Nov. and adult doe in Dec. with them. The buck was shot through shoulder and out off side,about 75yds, he just flopped and was DRT! The doe was shot at 80yds, but ran off and I found her 150-200yds later. A piece of lung was stuck in the off side exit hole blocking any blood trail. Both deer had quarter/half dollar size holes on both sides as the bullet exited.
I bought them from midsouth shooters supply and plan on using them in the future. I want to try T7 FFg loose and try for better groups when weather permits. I also understand they are going to come out in .45 caliber this year! They cost $8.78/15 pack and start easy just like powerbelts and have a short sabot that sits on the base. I recommend them to try. Did I mention I like them. :-D