Lyman "patent" breech

[dckcrk]

I have noticed that when I seat the ball in my GPR that the ball comes to a hard stop instead of feeling the powder crunch of the ball seating. It got me to thinking that the patched ball may be hitting the breech shoulder. I got to looking around and found a photo of a sectioned Lyman breech plug for a flintlock. According to my limited math skills the capacity of the breech is about 1.3cc or 20gr. of 3F. Since I'm using a 70 gr. charge something else is going on here or they changed the design of the breech? When the shop warms up enough I will try seating a patched ball against the breech without powder and using a syringe to determine the volume of water the breech will hold. Just out of curiosity. Or has anyone else already done this?

If it's your picture, Thanks.

Come to think of it the hooked breech of my rifle doesn't look much like this picture. My hook seems to screw into the back of the barrel like an internal thread plug. Hmmm.....curious.

 

[Valley Forge]

Duck Creek, I can tell you that I once had the dubious pleasure of loading a PRB into my GPR without first putting powder into the muzzle, and I had to employ the ball puller screw, which was a process of 75% panic and 25% frustration. It led me to buy heavy duty brass range rods with T handles, just in case. I also adopted a strict loading sequence with items arranged on the bench in a way that lets me know if I am missing a step.

ANYWAY, when I did load the PRB without powder (the missing powder was 55 grains of 2Fg), the ram rod went down further in the barrel, definitely enough to make it clear that the seated PRB was further down the barrel than it usually is with powder loaded first. That ram rod went far enough in to elicit the "Oh [golly]!!!" sinking feeling in the heart that one gets when one is new to this and realizes that one just made a typical, but unpleasant, rookie mistake. So, with powder, the PRB should not hit the breach area shoulder, EXCEPT that maybe 3Fg packs tighter down into that breach channel than 2Fg. I don't want to start another one of those wars of words about the surface area and space area of 2Fg vs. 3Fg, so maybe I'll just stop typing right here.

 

[BrownBear]

That would be an interesting experiment, but wouldn't it be easier just to mark your ramrod when your load is seated, then lay the rod along the outside of the barrel to measure where the ball rests in relation to the breech?

I read somewhere that the breech capacity is between 30 and 35 grains, but that probably includes powder that's settled into the flame channel. Whatever the case, if I push hard enough to feel the powder crunch, I can still feel it when I'm using a 35 grain charge. And I use that a whole lot for head shooting small game with my 50 and 54 GPRs.

 

[Greenmtnboy]

I believe your calculation of 20 grains is pretty close, give or take 5 grains.

 

[plinker]

I have a Pedersoli Kentucky pistol in 50 cal. My loading rod is marked at both the empty chamber height and for 25 and 35 grain charges. One day I was loading 25 grain charges and dry balled. I was sure that my rod told me that I had powder in the barrel. At home after I cleaned the barrel I dropped 20 grains of fffg down it and took a look. I could clearly see the step where the patent breech is. I emptied it and dropped 25 grains down. This time the step was covered. The patent breech holds about 25 grains and I learned that it will be difficult to see the difference between a dry ball and my 25 grain charge using the mark on the loading rod.