A while back JStanley exposed us to Bernoulli' Principle. If one examines the principle, and applies the knowledge to breech plugs, one discovers some surprising things, that are counter-intuitive.

Last winter i kept the Accura, and the V2 Accura loaded in my truck every night. Whenever the temperature would drop below zero, i took them rifle wrapped them in blanket, and put them in the back seat whilst i drove up to where i could shoot. When i pulled them out of the blanket the barrels stuck to my fingers, so i had to exercise care whilst handling them. I never once experienced a delay with either rifle.

The flame channel of the QRBP in the V2 was left 3mm most of the winter. A chamber in the powder end was created in the QRBP, by using a vent liner. A home made stainless vent liner was used through the winter. It began with a 0.029", and ended with a 0.030" flash hole.



Once whilst removing the carbon from the flame channel with a powered drill, i accidentally enlarged the flame channel to 1/8", which it is today. The picture also shows a Holo-Krome vent liner, not the stainless.

The success of this breech plug in sub-zero weather can be understood by examining it using Bernoulli principle. The smaller flame channel transfers the heat from the primer to the powder quicker than the heat would move in a larger flame channel. Also, the smaller flame channel has less surface area than a larger flame channel, thus there is less contact between the flame and the walls of the flame channel.

The Accura breech plug is similar, but different. It is shorter than the QRBP. Because the flame channel is shorter it carbons quicker, so i made it larger, not so much to ignite the BH, but so it didn't get plugged so quickly. The flame channel in this plug is 5/32". The flash hole began at 0.028", but has grown to 0.032" as pictured.





Both of these plugs were a perfect success igniting BH this past winter in sub-zero weather.




Myself, i know for a fact that enlarging the flame channel and/or flash hole is not necessary for successfully igniting BH209 in sub-zero temperatures.



Bernoulli principal tells us that the smaller the flash channel the faster the heat travels through it. The smaller the flash hole the higher the velocity of the flame when it hits the powder, the less pressure it exerts, and the hotter the flame. Thermodynamics tells us that less heat will be lost to the cold steel of the breech plug if there is less contact area.



Common sense would have us believe that enlarging the flash channel will help the heat reach the powder. Bernoulli' Principle shows us that this is incorrect; our intuition is wrong.

It seems that in the long breech plugs a 1/8" flash channel may be optimum. In the short breech plugs a 5/32" flash channel may be optimum.




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