GC's problem

[Lefty SRH]

I have 3 known accurate rifles and 3 known accurate loads. The problem I am having is the gas checks coming off sometime on mid-flight. I will have a nice group going and then have to 4"-6" flyer that ruins the group. What other tricks or ideas do you guys have to prevent the GCs from coming off in midflight?

[Bullshop]

What kind of gas checks?

[Lefty SRH]

Hornady, I bought some older ones that were for sale here on the forum and I think they are a little over sized. I have ordered another "newer" box to see if there's a difference in fit.