Wow! You just shoot your gun a lot it looks like. Any gas coming back would be very minimume from the looks of that plug. Buy a new one if you are scared about it. I use the same one I have had in my Encore since I bought it and I bought it the first year they were in production.

Like any rifle you get some gas blowback including centerfire bolt guns, autoloaders and every other type of gun I have shot. I just clean the whole gun anyways no matter what I shoot.