If when you load the gun, with the cock at 1/2 bent position, frizzen(hammer) closed, upon loading, lift the frizzen and see how much, if any powder is in the pan.
If there is powder there, you either need to enlarge the granulation size of your powder, or get a new liner.
When the vent is too large, you will lose part of the charge, out the vent.
I would suggest that if the vent is larger than .080", 3F would blast out the vent when the patched ball is seated. You might even lose 2F at that size.
At one time, the Brits sold rifles that were "self-priming" & this was thought to be a good thing.
All militaries of the world using paper ctgs., loaded with the cock at 1/2 bent and the hammer closed, on their flintlocks, as the paper ctg. also contained the priming charge.
The musket or rifle, was primed, then loaded. We don't do that these days, due to the possibility of the cock falling and discharging the rifle as it's being loaded.
However, you can test the size of your vent's powder loss, by closing the frizzen/hammer on an empty pan then loading the rifle as normal.