I've used the 340 gr Dead Centers out of my Omega with 100 gr T7 pellets. They were quite accurate at 100 yds.
http://smg.photobucket.com/albums/v445/HuntAway/?action=view&current=Zero50Cal2.bmp
and expanded nicely when fired through a 5 gal pail of black earth.
http://img.photobucket.com/albums/v445/HuntAway/BeforeAfter.jpg