Western Powders is one of the companies that makes an CVA breech plug for reliable ignition of Blackhorn powder. And the bullet maker Lehigh is another.
While the thread below describes making a breech plug with a drilled out screw as a replaceable vent, there's also relevant information about how to modify one's own breech plug to ignite Black horn better.
If you read through the thread, it's mentioned that a vent hole measuring between .28 and .35 can work well for igniting Blackhorn.
However the length of the flash hole may also be an issue.
One method is to dish out a small powder chamber of about 1/4" deep in front of the flash hole. It would expose more powder to the primer flash, and possibly also reduce the length that the flash needs to travel.
Building a good breech plug for ignition is both a science and an art.
And that's why CVA charges $20 to buy their special breech plug for Blackhorn 209 whereas TC guns have a good enough breech plug right out of the box. While others simply modify their own plug by buying a spare breech plug and drilling it themselves with a drill press and maybe a Dremel.
http://www.huntingnet.com/forum/blac...questions.html
For instance
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If one modifies the breech plug supplied with CVA rifles, one can do 2 things that make for a flash channel with a larger volume. Simplest is to drill the flash channel larger using a 5/32" drill. Next, make a chamber on the powder end about 1/4" deep, and tap the flame channel so it will accept a standard vent liner. After doing these steps the modified breech plug is 100% reliable igniting Blackhorn powder. This modified breech plug will have a flash channel with far more volume than the 'made for Blackhorn' breech plugs. Another advantage this modified plug has over the Blackhorn plug is, it has a replaceable flash hole, in the form of a vent liner.
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Lehigh liners are hardened and designed to wear longer. The flash hole is cut to be 0.031 +/-. This is less than than Western Powders wanted for the ignition of BH-209 but I believe over time it has been proven that it is very effecient for the ignition of BH. I my self have used the .031 flash hole, shot Remington 209-4's primer (410 primer) with BH and have 0 ignition problems with the powder.
A second advantage of the Lehigh might be two fold, with 0.031" flash hole and the domed shape of the external portion of the vent liner it helps reduce blow back pressure felt on the nose of the primer or blow back pressure felt in the breech.
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New vents are purchased with flash hole of 0.031" to 0.033" depending on brand. This, to me seems too large. The pictured vent is home made, and has a 0.028" flash hole. It works good. My thinking is why start large, when time and shooting will get you there anyway. It is my understanding that commercial vents are really made and sold for smokeless shooters. It is my opinion that commercial vent flash holes are too large. My home made vents have never failed to instantaneously ignite BH209 powder in sub-zero weather. Experiment has demonstrated that a 0.028" flash hole ignites powder just as efficiently as a 0.033" flash hole.
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