As promised....
This afternoon I took my barreled action over to a friend with a small shop and we turned some .500 brass round stock.
We started by turning a brass pilot to .349 and it would not fit into the muzzle. We decreased it in .001 increments, .348 no go, .347 no go, it would only fit into the muzzle at .346. We then cut off the plug and cleaned the ends to see if it would slide through the bore, it did not. The bore got tight about 5 inches back from the muzzle and I had to tap it though the rest of the way. This tells me the bore is not .349 but more likely .344-.345.
This also tells me I was correct in how to measure a slug of this type of 3 groove barrel, where you can get a caliper to measure across a groove and land, then add 1 groove depth for groove diameter or subtract 1 groove depth for bore.
Since JES advertised his .35 calibers as .349 bore and .359 groove, I gave him a call. He was still a bit reticent to listen, he told me that he had obtained some of the Federal ammo I used and thought that his chamber reamer produced a throat that was too tight for this modern ammo. He told me how the rifling process can leave sharp edges on the lands which can make the bore seem smaller but that will wear away in a few rounds. When I told him I had put about 60 rounds through the gun he agreed it was a non-issue.
In the end I told him all I ask was that he redo the process again so that it measures the stated .349/.359 and he said he'd be happy to do that. At the same time he's going to rechamber with the new reamer to ease up the throat dimension and, at my request, also check the headspace to make sure the pressure spike didn't set back the lugs, though he highly doubts it did. I just hope it's as accurate.
The gun is off to him tomorrow, when it comes back with the correct .349/.359 I'll consider the matter closed and am on my own with it from here on in.
All in all, a learning experience, didn't lose any fingers and have a freezer full of moose.
