Thanks for the suggestions. While I don't really want to remove my scope, I will look into the Shockwaves. I had the forepiece of the rifle resting on a folded towel and was careful not to rest on the barrel itself.
I have had the disc rifle for a long time and up to last year I shot a 300 grain Barnes bullet which shot very well but I thought if I went to a lighter bullet it might give me a little more range with less drop. I surely won't sacrifice accuracy fora little longer range however.