Quoted:
Thanks, I'll check it out.
In the absence of this tool, though, what's the best way to get a good estimate? I've taken some test rounds and painted them with black magic marker. It seems as though I'm getting feint land prints on them even at 3.680". 3.65" seems cleaner. Maybe it's just me and my eyes playing tricks... but shouldn't I be able to go out to at least 3.68" without touching the lands?
I'm sure you're misinterpreting the manufacturing marks for rifling marks. You need to reseat the bullet back into the case, to the point on the bearing surface, where the ink rubs/scrapes off. That's a lot farther out than 3.680" like I said.
Do it again and do it more than a few times with different bullets and then average them all together for your COAL. Or buy the tool.
Chris