Yes and no. Using a chronograph to measure changes in velocity as you open up the TH, one numbered drill bit size at a time, will tell you what you are losing out the MUZZLE.
However, one of the reasons that the Chamber's White Lightning liners out perform expectations the affect that the parabolic cone on the inside of the liner has on escaping gases. The parabolic design uses the expanding gases against the gas trying to escape, by forcing some gases back towards a focus point in the liner's base( closest to the bore.) The higher the gas Pressure pushing on the Parabolic surface, the more the gas acts like a "Plug", for just a brief millisecond- all that is needed to insure good combustion of the powder, and enough pressure to send the ball out the barrel.
The Vent on any flintlock- no matter how designed-- acts as a Pressure release "valve" in a flint ignition rifle or smoothbore. The Bigger the opening, the more gas escapes. What the parabolic designed liner have done is use a bit of aerodynamic design ideas to use the gases to block the escaping gases, just enough that you get more consistent, and higher chamber pressures, for a millisecond or two longer, using that liner than using a straight line cone, or drill hole for that TH.
So, the gas does escape FASTER from a larger TH, but the actually timing of the escape may be DELAYED a bit. That should be just long enough to keep the pressure in the chamber high enough, long enough, to burn the powder more completely, at higher temperatures, and send the PRB out the barrel At slightly faster speeds, than when no liner, or a liner other than a White Lightning liner is used.
I don't have the equipment to measure burn time in microseconds- I doubt anyone outside a sophisticated lab would have such gear. However, you can KNOW that something exists, by the results you see using chronographs.
When I was drilling my TH out one size at a time, I was Not interested in changes in velocity: that could be made up for by increasing the powder charge. I was ONLY INTERESTED in getting my flintlock to STOP misfiring.
If I were wanting to test the efficacy of given THs, I would begin with a new barrel and run tests on velocity with a drilled hole-1/16" to begin, and then go up one drill size and re-test, and record results. I would stop at 5/64", since there seems to be a general consensus that above this diameter, velocities drop off pretty fast.
Then I would drill and tap the same barrel for a liner, using a straight cone liner first, testing it "As is" in its inside coned format, and then replacing it with a new liner, and coning the exterior for another battery of testing. When I was done with those tests, I would install the White Lightning liner and repeat the testing again.
I suppose of you have access to time-lapse photography equipment( very expensive) you could take pictures of the vent to determine the beginning and ending of the smoke and gases exiting the TH. That would give you some kind of idea in milliseconds as to how long the various sized THs impeded the complete burning of the main charge, and the exiting of the ball from the muzzle. If you had two such cameras, you could set up one to aim at the TH, and the second on the MUZZLE, to get a very good idea on any change in " barrel time" for a given Vent size, liner, and barrel length.
Someone else can do this. For me, shooting my flintlocks is my hobby. I have no interest in making it that much work. My hat is eternally off for the patience, and work that Larry Pletcher( Pletch, here) has done with his computers and time lapse cameras. :thumbsup:
