Some commercial flintlocks have a "Powder chamber" in the breech of the barrel, and a channel leading from this chamber to the side of the barrel where the vent hole is exposed to the flash pan of the lock. In these kinds of gun, you have to have powder right next to the TH( vent) for best ignition.
With Tradition Flintlock rifles, with flat-faced Breech plugs, and NO POWDER CAVITIES, the hole to the side of the barrel is very short in length. A TH LINER, like the Chamber' White lightning helps ignition two ways:
a. It has a parabolic Curve to the sides of the inside opening of the TH, which causes Gases to push back AGAINST escaping gases as pressure rises, during ignition of the main powder charge, causing the pressure and heat in the barrel to rise even faster, burning the powder more efficiently, and faster.
b. the parabolic curve allows a vent pick( TH PICK) to be used to open a hole in the main powder charge, WHILE LEAVING some powder around the INSIDE of the liner for quick ignition. The hole in the powder then allows heat to ignite even more granules of powder in the barrel, speeding ignition of the main charge.
Is the parabolic Curve better than a straight "inside cone"? The answer lies in what the parabolic cone can do that a straight sided cone can't. A straight sided cone( think of a tipi turned on its side) can funnel smoke( gases) out the hole compressing the gases to move faster as the cone narrows.
The parabolic cone does this, also, but the curved surface pushes some of the gas against the following gases, slowing or stopping some of the gas from escaping. The slowing ( this all happens in milliseconds) causes a rise in both pressure and temperature inside the barrel as the main powder charge ignites, speeding ignition, and more completely burning the granules before the projectile leaves the barrel. As the pressure drops, more gas can now escape from the TH( vent), and does, but with the gases reflected back by the parabolic cone surfaces continuing to hold back some of those gases. Some say there is a small increase in MV when the parabolic liner is used, but,IMHO, it would be so small that it would be difficult to isolate from other factors that affect MV.
Outside countersinking simply moves a bit of powder closer to the inside of the barrel. But, with the space between the barrel and pan being what it is, in any given gun, I don't really want to be putting any priming powder where it has to straddle a crack that might allow "fines" to slip down behind my lock into the lock mortise where ignition might damage my gunstock and lock.
To each his own, however. :shocked2: :surrender: :thumbsup: :thumbsup: