I will second the fact they had a few different breech plugs on the encore guns
II know I had a lot of issue's with mine and (barrels too, gun was just a BAD one IMO< it was sent back to TC several times, and had many personal chats with Greg there, where even they couldn;t do better than a 2 inch group at 50 yards) )
I was also given a few different breech plugs to try before gun went back to them!

in the end could NEVER get gun to shoot well consistently, ( and I tried like heck, been to a few custom rifle makers shops too and they gave up as well, I must have spent a grand or more trying to make it work, at some point it became a mission more than a need ), and the list of things I had done to that gun is crazy, not to mention an easy 500+ rounds down barrels trying things!

and after it all, I had to admit defeat and sold it !
TC wouldnl;t stand behind the gun either by the way, they TOLD me straight up a 2 inch group is more than accurate to kill deer and that was all they could get the gun to do and this was at 50 yards on there test range!(also one of the reason I sold the gun, wasn't happy they had so little care in things and I knew Greg personally for yrs prior to this!)
a shame as I know so many with them that are just super accurate reliable guns!


so I know for a fact there are a few different versions of breech plugs,
so depending what one your's has might be a slight cause in things

I never had any delayed fires with any design I had and I did use BH 209 powder, but I am sure its possible pending the designs nd how well a charge is packed in the bore
I can also tell you many primers are just NOT as clan as others and can block the hole more than others with build up!