Frustrated with my chamber cast.

[jconley]

Many members here have given me great advice as I’ve started playing around with my 45-120 over the last few days. Thanks for that.
I cast the chamber last night using Certosafe, everything went fine and I was rather thrilled at how the cast turned out. Unfortunately I can’t seem to get a repeatable measurement on any part of the cast.
Using high-end calipers or really nice micrometers, all measurements are really inconclusive.
Even just getting an accurate measurement on what would appear to be the easiest surface, the free bore, it’s difficult. I’m getting A plus or minus of .002.
Have other people experienced this sort of problem?

[redneck1]

Its awful hard to take accurate measurements on a tapered surface .
Short of investing in a surface plate , v blocks and a height gauge I'd say take a best guess at an average and call it good

[jconley]

Its awful hard to take accurate measurements on a tapered surface .
Short of investing in a surface plate , v blocks and a height gauge I'd say take a best guess at an average and call it good

Thank you, I’m wanting to get a new mold, and plan paper patch. Where does my final number come from when ordering a mold? The smaller number from in the lands, or the larger number of the bore?

[oley55]

Thank you, I’m wanting to get a new mold, and plan paper patch. Where does my final number come from when ordering a mold? The smaller number from in the lands, or the larger number of the bore?

groove diameter

[jconley]

groove diameter

Thanks.

[redneck1]

I think you might be better served asking up in the black powder paper patch forum .
I happen to be fairly ignorant of the subject but I do believe a larger number of people subscribe to the bore diameter method of patching .

To much voo doo for me I'll stick with lubed lead

[oley55]

I think you might be better served asking up in the black powder paper patch forum .
I happen to be fairly ignorant of the subject but I do believe a larger number of people subscribe to the bore diameter method of patching .

To much voo doo for me I'll stick with lubed lead

Stupid me, I should pay closer attention before I run off at the keyboard, you are correct. as per "the Paper Jacket" book by Paul Mathews, page 21, "Paper patched bullets for use with smokless powder should have an unpatched diameter equal to or .0005 inch over the rifle's bore diameter." Prezactly as written.

conversely for black powder an unpatched bullet should be .004 - .006" smaller.

pm on the way to the OP.