Further to Taylor's post above, when using the mic and cranking on the barrel, the force generated due to the fine thread is so extreme as to produce #'s that are meaningless.
The 12 oz. denim I spoke of, measuring .030" with squeezed calipers, I can actually get down to .005" with my mic. by really cranking on the barrel.
Some of the guys on this forum cannot load a ball .005" under bore size with a 10oz. denim I measure at .022" to .0225" using my calipers. I just cranking down on that material with my
mic and got .001". That's 1 thousandth of an inch. So - what is it, .001" or .022/5? Calipers and mic, both v/hard compressed.
I believe you should find a material you can load with, that shoots great and does not allow fouling to build in the bore- thus never needs wiping while shooting. That is my criteria. What the material measures with whatever tool you use, is immaterial (yeah - pun intended), but if it works for you, stick with it. I know, that if a material measures .022" with my dial calipers, it will shoot
well in most of my guns.
Joanne's fabrics sells denim listed in ounce weights. I have found that 8oz. will shoot fairly well in guns with square rifling, when using a (dead soft) ball .005" smaller than bore size.
If using a .010" undersized ball, 10oz will likely shoot better and be more accurate(with either ball). With rounded (deeper) rifling you will likely find you need a .005" undersized ball AND 10oz denim.
The light canvas that measures .022" with my calipers (compressed) loads harder for me with a .005" undersized ball than the 10oz denim I have, but - it shoots better and seals better in my GETZ .50 bl. I can still squeeze that down to whatever I want with my mic. abusing that instrument totally.
with rounded rifling.
To load tight combinations, which I find shoot best, requires a smoothly crowned barrel. The better this polishing and rounding of the corners cut by the bl. maker's machine, the easier loading you will have with ANY combination.
DaveC makes a tool to cut this crown.
Using different grades of emery or wet/dry paper and the end of your thumb, you can 'grind' this crown yourself. Some minor modicum of skill is required. Rotating the barrel frequently will
make this crown perfectly even.