This is one of the most unique in design and quite often carried over into smokeless muzzle loader builds. The most popular build is the .45 with the .416, .40 and .375 coming from the rear. In most of these builds the Savage BP is the first choice for their build.
So why is this BP so popular? Understanding how it operates might reveal some of the reasons why.
Attachment 28153
We basically install a 209 primer at one end and at the other end a vent liner with a particular size orifice. In between we have a gap that is often referred to as the Flame Channel that serves a dual purpose.
Before I go any further the principle of operation I’m about to share has been accepted as such by many others and not simply concocted by me.
When the primer is detonated it dumps a good amount of thermal energy into the flame channel which in turn is bled off in a regulated fashion by the vent orifice into the bore to ignite the powder. As powder in the bore ignites it begins to build pressure to a point that any further feed of thermal energy is stopped from the flame channel and now bore pressure again regulated by the vent orifice will start to flow back through into the flame channel. The flame channel now becomes a cushioning reservoir so to speak to reduce max pressure the spent primer will be exposed to.
What some deem as the weakest link in this design is the vent liner because of the wear of the orifice hole. To extent the vent liner usage you can use a stronger grade material but you have to make your own. The material normally used for purchased vent liners is Grade 8 material. You can purchase Grade 12 material screws but IMO you need cobalt drills to get a decent number of vents drilled per drill.
Another approach being developed for a vent liner replacement is using bushings of hard material such as tungsten alloy or even pure tungsten. The required orifice hole is being accomplished with an EDM process. Then the Breech Plug is modified for the bushing and secured with a retaining fastener that is screwed over the bushing. Sorry I don’t have a picture of this off hand to share.
Some of you are probably aware of ignition systems that employ Large Rifle Primers and modules. For my purpose the 209 is simple and functional so at the moment I have no interest in possibly changing it. Just a mention that I do know it exists.
Just a final note.
The volumetric space of the flame channel does play an important role and if you want to have a little fun you can actually calculate the volumetric space by using this formula.
Pi x radius squared times x length.
Ed