Final update. Christmas and family stuff put this project on the back burner, but I also needed to buy some additional stuff to finish the project.
What follows is not intended to change anybody's mind or suggest they change whatever cleaning regimen works for them. This is just what worked for me. This is a long post in the hope it might help someone who doesn't already have a self-proven cleaning regimen.
First, my general preference is to let chemistry do the work and avoid mechanical action as much as possible. My No. 4 Mk II is a little older than I am, and I have no idea who did what, how often, and how well in the past. I'm concerned about the lands and grooves remaining as intact as possible in a rifle this old. So for me, Patch-Out is is.
Because I continued to get muddy & blue patches with the Patch-Out, I called Terry Paul, owner of Sharp Shoot R, maker of Patch-Out and Accelerator. He was very friendly and extremely helpful, and pointed out a couple of things I was doing wrong.
First, he strongly recommends NOT using brushes at all, except for a nylon brush as described below. Absolutely no brass brushes.
Second, any brass tools used (cleaning rod, jag, brush, etc., will cause the patches to continue to come out blue until the cows come home because the Patch-Out is leaching copper from the brass tools. In computer programming terms this would be called an "endless loop."
Third, for an extremely dirty bore like mine that doesn't clean up with simple wet patches, he recommends using an Accelerator/Patch-Out mix to run a well-soaked NYLON brush on a fiberglass rod ONCE through the bore until the brush tip is barely out of the muzzle, then withdraw it. This causes the Patch-Out/Accelerator to foam in the bore, which results in a more thorough chemical cleaning.
In my case, with the bore as dirty as it was, I let this sit overnight. Next day I ran a clean patch on a plastic jag through the bore. It still came out a bit blackish with some blue. Repeated the process the next night and following morning. The second procedure resulted in a "clean" patch with no color.
Terry recommends that following a thorough cleaning resulting in a clean (no-color) patch, you do what he calls a "Proof Test." Run a patch well wetted with Patch-Out through the bore. Let it sit for 10 minutes. Run a clean, dry patch through. If the patch comes out clean, the bore is completely clean. If not, repeat the overnight process described above
I got a successful Proof Test, so on to the bore gauges. It was suggested I buy them from Apex, which I did, but I wish I'd done some checking first because they are $40 each there but 20% cheaper from brpguns.com. Oh well, got what I need, and the barrel specs perfectly per the gauges.
I haven't yet bought a bore scope so can't comment on erosion. Regardless, I'm not going to replace the barrel even if I have pitting.
So now I can reassemble the rifle and should have time to shoot it in a couple of weeks. Weather here has been summer-like but I'm too busy to step outside to shoot (I live in the mountains so no formal range needed!).
This was a long and more complex project than originally envisioned, but now I'm sure my bore is in good shape so we'll see how well it shoots.
