I have had encores for years and used Win 209 reloading primers most of the time never have had a misfire. The win 209 is a bit longer than the other 209 primers and seals better. I believe TC designed their guns for the win 209 because it is the longest and assumed any shorter ones would work.
You should clean the carbon out with a drill about every 10 shots it can cause your problem. A short bushing [firing pin] could also. If you use shorter 209 primers you may have to shim to cut the blowback.