General question about bore size of Pedersoli 45/70

[Pb2au]

I have an ongoing PP project for my Pedersoli Rolling block, 45/70.
In the process of working out the final diameter of the patched bullet, I came to the realization that the bore size of my barrel is relatively small in comparison. When measured, it came out to .445". Now mind you this was measuring the slugged lead with a pair of calipers, so there may be a wee bit of error, but close enough for the girls I dance with.
When I was developing the final patched diameter that would snug up into the bore, I arrived to a final size of .4445"-ish. So at least that mostly agrees with my slug measurement. I have a plan in place to more accurately measure the bore, involving 1) a chamber cast and 2) using a drill shank and wrapping brass shim to build up to a fit for the bore then measure.
So what I am getting at is that i was expecting a bore around .450-.451", but was surprised at the smaller dimension. The groove dim came it right at .4575", so no surprise there.
Anyone else run into a similar situation? Mostly just curious.

 

[RBHarter]

Sounds like a true BP bbl with deep grooves to displace the powder fouling . The .012 wrap I think will be the challenge but as a guess 20 or 22 lb paper should get you in the "groove". Pun intended.

 

[9.3X62AL]

I got a surprise of this sort when I set out to learn the X/Y of the CZ-550 I have in 9.3 x 62 Mauser. Slugging the throat (.3665") and grooves (.3660") showed no surprises, but the bore was/is TIGHT--.352" pin gauge is a draggy slip-fit, .353" is a no-go. Doing the math, the barrel has 4 lands of .007" height.

What Does It All Mean? I dunno. The rifle is accurate as can be, it shoots every jacketed bullet I've tried from 250 to 286 grains into 1.5 MOA or better with one exception--the Speer 270 SSP refuses to group. Castings of 270 grain weight shoot even better than that, 1.25 to 1.5 MOA is the rule between 1500 and 2000 FPS. (Let's recall that the 9.3 x 62 is NOT a rat-shooter, it's for big critters with surly outlooks. 1.5 MOA is "gilding the lily" for such applications). Early in the game I wrapped some pure-lead Lyman #358430s to .368" with 9# airmail paper, and shot them at one of the NCBS meetings just for grins. 2"-class groups at 100 yards, with open iron sights. The 550 now sports a Leup 2x-7x, I should re-visit the PP option with its improved vision.

 

[Pb2au]

Sounds like a true BP bbl with deep grooves to displace the powder fouling . The .012 wrap I think will be the challenge but as a guess 20 or 22 lb paper should get you in the "groove". Pun intended.

That is kinda what I figured. Nice pun BTW.

Now where I shot myself in the butt a little is I ordered my mold WITHOUT slugging the barrel and knowing the bore diameter. I assumed........450",,, F- for me...
My strategy is to patch to bore diameter to start out. What all this means for me is I had to go to thinner paper to make up the difference. Right now, 9# onion skin is coming in at 0.0015", so that puts me right at .4445" patched and dried. (Mold is dropping at .441" on the money)
The chamber end of the barrel has a tiny bit more windage than the muzzle, so it tucks right up into the lands.

This has turned out to be a very interesting project.

 

[Ian]

My Shiloh has a .450-ish bore, perfect for smokeless powder and .452" cores. As RBH said, yours is probably optimized for BP.

 

[Ian]

Missed your last post Pb, I should have mentioned that muzzle end measurements aren't worth much, need a chamber cast or test-fit with various bullets to get the true land dimension at the chamber end just ahead of the throat.

I've run BP with both plain lubed bullets sized to .459" (30:1 or so alloy) and sized .452" and patched. Patched always performed better regardless of powder type or alloy but with BP seemed to require some bore maintenance (I should have used a lubed wad in addition to the grease cookie). With a heavy load of modified Emmert's lube the un-patched bullets could go a lot of shots without cleaning.

Only way to find out is go shoot. I'm interested in how fouling accumulates in your rifle's throat and if it gets bad in a few shots, what can be done to fix it. I strongly suspect the secret to controlling throat fouling with PP and black powder lies in the combination of throat fit and the lube delivery system.

 

[Pb2au]

"As RBH said, yours is probably optimized for BP."
I've always been more lucky than good! The gentleman I purchased the rifle from was BP enthusiast, so it makes sense. I ran into him at a rendevous in Friendship Indiana and he was selling the rifle there. A fine fellow, he gave me some good info on loading with BP, what he found the rifle liked and so on. Good chap.

Well the proof of the pudding is in the eating as they say..
Hopefully I will have some finished cartridges tonight or tomorrow, then if the weather cooperates it is off to the range this weekend!

 

[Pb2au]

Missed your last post Pb, I should have mentioned that muzzle end measurements aren't worth much, need a chamber cast or test-fit with various bullets to get the true land dimension at the chamber end just ahead of the throat.

I've run BP with both plain lubed bullets sized to .459" (30:1 or so alloy) and sized .452" and patched. Patched always performed better regardless of powder type or alloy but with BP seemed to require some bore maintenance (I should have used a lubed wad in addition to the grease cookie). With a heavy load of modified Emmert's lube the un-patched bullets could go a lot of shots without cleaning.

Only way to find out is go shoot. I'm interested in how fouling accumulates in your rifle's throat and if it gets bad in a few shots, what can be done to fix it. I strongly suspect the secret to controlling throat fouling with PP and black powder lies in the combination of throat fit and the lube delivery system.

I am aligned with your curiosity about the fouling of the throat.
In between Matthews books and Mr. Venturino's book, (thanks for the recommendation on that btw), both go into some very good detail on fouling management.
From what I am gathering, there seems to be two schools of thought.
1) Wiping the barrel out between xx shots. Wet/dry/dry.
2) Managing the fouling directly with (as you mentioned already) lube and fit strategy. Which really goes part in parcel with general cast bullet protocol.

I am going to split the middle to start out.
Powder/card wad/ lube cookie/ card wad/card wad/ bullet.
Then shoot and see what is happening in the barrel. The wiping rod will go with me for the first go round to wipe as needed.

I am pretty excited to see what the gun says to my ideas.....