It sounds like your rifle is shooting well, and that does not surprise me. It's a great rifle. As for the primer problem, I have never, and we are taking over 1000 primers of the Winchester W209 primers had a misfire with them. That is one reason I rely on them for most my shooting. Although I have tried the Remington Kleenbore Primers and like them a great deal as well.

I am not sure of the hammer, fireing pin design of the rifle you have but perhaps someone else could comment. I might suspect that perhaps the firing pin is not sliding smooth or the hammer striking hard enough. I really have not had any problems with the primers you mentioned...

I am sure there are other Sidekick owners that can help you out with that matter.... if not call or email NEF and ask them what might be causing that problem..