Pistol breechplug modification

[andy49]

I am trying to get information on a breech plug modification that a famous contemporary builder, Bill Kennedy, was doing to his pistol builds. He machined out the face of breech plug for better powder efficiency.
I would like to know the depth to the plug face he used as ideal.
Thanks
Andy

[Dphariss]

I think what you are looking for is described here.

http://americanlongrifles.org/forum/index.php?topic=32573.0

[Chris Treichel]

I'll be, this produces a Munroe effect.  Had lots of fun with that back when I was a Marine getting trained by the engineers in the deconstruction business. What you are looking for is a focus of the shockwaves from an explosion combined causing a plasma jet. Parabolas cause this effect.  Didn't think this would be something you would see in muzzleloaders, but it makes sense now. Since blackpowder burn is too slow to cause a plasma jet you probably would just focus the blast at ignition increasing the velocity of the burn of the remaining powder.

[Don Getz]

Bill was a good friend of ours.   He made many trips down to the barrel shop to pick
up barrel material.  We did smooth and rifled blanks for him.  Bill also had his little pet
squirrel with him, it would peek out of his shirt.   As for his special work on his breech
plugs, he also believed that if you got the touch hole too far forward on the barrel it
would increase the recoil.....all of the powder behind the touch hole would be pushing
to the rear.  Bet you never heard that before..........Don

[andy49]

Thanks Dan, that is what I was looking for.
I am building a 45 cal and was wondering if a dished out breech plug face with a touch hole liner (.25"), would place a light load out of range of the vent (to far back)?
Andy

[Dphariss]

Thanks Dan, that is what I was looking for.
I am building a 45 cal and was wondering if a dished out breech plug face with a touch hole liner (.25"), would place a light load out of range of the vent (to far back)?
Andy

45 will need a 7/16 ball end mill to get a cup just smaller than the bore. Getting one the exact size would be expensive.

Dan

[rtadams]

10-05-14

andy49,

I would do as Dphariss suggest but take the machining process one step further. Machine the breech plug cavity to transition from the bore diameter at the face of the breech plug to the 7/16" ball end mill cavity.

Best Regards,

Robert

[Dphariss]

10-05-14

andy49,

I would do as Dphariss suggest but take the machining process one step further. Machine the breech plug cavity to transition from the bore diameter at the face of the breech plug to the 7/16" ball end mill cavity.

Best Regards,

Robert

Given the difference is only about .013" or .0065 per side this is not worth the trouble. When using any breech with a cavity care must be taken in fitting the breech plug so that pressure against the internal shoulder is not so great as to form a burr that can protentially trap a patch. This can be corrected with needle files if need be.

Dan

[Chris Treichel]

I would suggest looking at this as a parabola (not a hemisphere) and the perfect location for the touch hole should be at the maximum to achieve something close to the Munroe effect. 

[davec2]

Although the data seems to show that the hollow breech plug may add a couple of percent to velocity, this is not the same as the Munroe effect.  Black powder is a "low explosive" which does not "detonate" but rather conflagrates.  As a low explosive, it cannot produce the detonation shock wave that makes a shaped charge work.  This is a good thing for us...if black powder could produce the detonation velocity required to produce the Munroe effect, we would each only get one shot out of a rifle. 

Interesting data none the less, and I often use a ball end mill to hollow out the face of a breech plug, but only because I think the breech is easier to keep clean without a sharp corner.

Breech plug in a tool I made to hold it for machining in the lathe.....

[Chris Treichel]

I agree, if blackpowder was fast enough it would cause a plasma jet which is what the Munroe effect is used for... cutting charges.

But for this purpose and what I think Kennedy found was that by having a cup shape caused a focus of the blast