I have had several Chambers liners. "White Lightening" I believe they are called, and they are just fine.
I have also drilled the standard vent liner, from the back, with a #1 Countersink, and that seems to work quite well, and cost a bit less.
On the other hand, I have an old .69 cal that has no liner, just a plain ol' hole, and that seems to work okay too.
However, it has taken it from the late 1960's until a few years back to become large enough to work really well!
Typically speaking, the size of the hole makes all the difference and there is no real agreement on the best size.
Others may argue it's the location of that vent hole in relation to the pan, and If I were an arguing man this is the side I would take.
Not much help, I suspect. But the two factors mentioned, size and location, is something that needs to be worked out each individual rifle......that would be my best guess.
Uncle Russ...