45-70 Barrel Dimensions for Paper Patching

[Rbertalotto]

Today I decided to inventory the various 45-70 rifles I own with regard to their internal barrel dimensions

Measuring "bore" diameter proved to be difficult because of the various number of lands and grooves and the twist on the driven slug.

I ordered a set of precision ground pin gauges .250 to .500 (negative ground)



Using these pin gauges and verifying the numbers with an expandable Ball Type Hole Gage I was able to arrive at relatively accurate numbers.



Once I knew the bore, I wrapped various pin gauges with two layers of #9 Onion paper that I sourced through Buffalo Arms

Using this method I arrived at the exact diameter I needed for a bullet if I wanted the bullet and the paper to ride on the lands. To this number I'll add X inches to arrive at the casting mold dimension I'll need.

I'll then turn a "D" Reamer on the lathe and proceed to cut a paper-patch bullet mold.

Does this sound like I'm headed in the correct direction?

45-70 Rifle Barrel Dimensions
Paper Patch #9 Onion / 25% cotton = .0016”   (Double Wrap = .0064”)


RIFLE BORE GROOVE BULLET FINAL
PEDERSOLI
Rolling Block (Pistol Grip) .4500 .4570 .4450 .4513
PEDERSOLI
Rolling Block (Straight) .4500 .4553 .4440 .4504
PEDERSOLI
1874 Sharps .4490 .4575 .4430 .4488
H&R
1884 Trap Door Officers .4490 .4575 .4430 .4488
WINCHESTER
1886 (Japan) Take-Down .4500 .4563 .4450 .4513
WINCHESTER
1885 BPCR (Badger) .4500 .4560 .4450 .4513

“BORE” measured using negative gauge pins
“FINAL” is negative gauge pin wrapped twice with patch paper and a tight fit without paper tearing.

3-21-15

[Rbertalotto]

Sorry the chart didn't copy from "word" properly

The four numbers are "BORE" . "GROOVE", "BULLET NEEDED" ,"FINAL WRAPPED SIZE"

[Lumpy Grits]

Most 'peters' have bit of choke at the muzzle.
Those hole gauges only tell you the size at the point you measure. As a machinist for over 40 years I'll tell you that I don't like them.
You'll get a much better 'read' with a camber cast that includes the bbl throat/leade.
Or-You could also drive a lead ball from the breech to the muzzle and measure that.
Gary

[Rbertalotto]

I drove a pure led, oversized bullet from chamber to muzzle and from muzzle to chamber a while ago. This the only accurate way to measure the groove diameter and to check for uniformity . That I understand for lubed bullets. The issue was coming up with a relatively consistent way to measure bore diameter.
The hole gauge was only used to confirm the pin measurement.
Thanks for the comments, much appreciated!

[Gunlaker]

That's exactly what I did for my .38-55 before ordering a new Brooks mould. The technique worked very well for me.

Chris.

[Rbertalotto]

Good to hear Chris!