I'm shooting a Knight LRH with Nikon BDC scope. Last year I was sighted-in; 3" group at 100 yds. I went to sight-in this year and couldn't get a good group. I'm using the same pellets and bullets as last year. I'm now going to try loose powder, and a couple of different bullets. Before I start the sight-in process, does anyone have any ideas what may be wrong and/or suggestions for correction. Thanks.

Ed