Great to hear a thorough rundown. I agree with Rex, don't let the fouling scare you. If it was a target rifle that would be frustrating for reasons I'll detail in a minute, but if you're not trying to shoot 50 rounds in a sitting there's nothing inherently wrong with a rough barrel. I don't know anyone who would sit down and shoot 50 35 Whelen rounds but you never know. It's going to be fine, enjoy doing the other parts of the build. Rough and damaged are not the same thing.
I had a Savage barrel I considered to be very heavy fouling. It shot great when it was in equilibrium but it took lots of shots to build the barrel back up after I stripped it and then I only had about 50-70 before the copper would start causing pressure or inaccuracy. I could put a pot roast on, go to the basement and start swabbing and I'd still be getting blue when dinner was ready. So I eventually just decided that I wasn't going to take all the copper out since I was wasting shots to put it back. Unless the barrel is polished it's going to need some copper laid in to function correctly.
I don't think the fouling is going to interfere with break in necessarily, except that you could hypothetically run into pressure spikes before things smooth out. Pressure spikes can result in bad bolt lift, but I doubt that the hard bolt was from too much copper buildup and pressure (it is possible, I've experienced it.) Probably just new barrel dynamics with the variation that comes with factory ammo. It could literally have been some micro-crud from the smithing. WHat I'd see when I got to too much copper was a sudden shift in point of impact or drastic increase in the severity of fliers. Then some general crankiness in the breech. At any rate, whatever system you use, what break in is really doing is knocking down imperfections using heat and pressure. The imperfections in the throat have a big effect on the copper in the entire barrel, according to people I trust. As that area gets tamed the rest of the barrel gets down closer to building up whatever copper is deposited there physically, with less vaporized copper from a rough throat being available to deposit as condensation. Or so I understand it. Essentially it'll get better.
So, having said all that about it not really mattering I personally would 100% do a DIY lap of some sort. You're going to have this thing a while, might as well not worry about it. I know there's a lot of guys out there who clutch their pearls and pass out at the idea of abrasives but bore treatment has attracted more myths and false rumors than a middle school prom. Like the guy who sings louder at church to prove how great he is, a lot of people just repeat sanctimonious garbage to sound knowledgeable. Tubb's fire lapping kits are a fantastic idea, I bet you could find another whelen fan on here to load a kit up for you if you sent him the kit and your empties. Another method I got from knowledgeable people on both sides of the world is to physically scrub the barrel with fine scotch pads. It needs to be done systematically, and you don't want to leave the end of the barrel, but it's not hard. You take a pad, cut a thin strip, cut that in half, and stretch it over a brush. That's basically it. I have not shot a barrel I did this to but I've tested the method on a takeoff and I would absolutely do it if I needed to, or I will when the throat on my current barrels need to have crackling cleaned up. Even if you only did the first six inches for 20 strokes, then the first three inches for 20 I bet you'd cut the copper deposits by a lot. My buddy who used to compete at a grand actually went so far as to do this to a new (fully lapped) barrel: get a hardwood dowel sanded to the size of your bore, hammer the dowel with green or red rouge paste, chuck the dowel in a drill and use it to wear down/polish out the throat. He'd literally ruin his lands (or actually extend them a thousandfold) to get longer life and less fouling. I'm not recommending that, it's just an example to illustrate that there's a lot you can do and that it's a lot harder to ruin barrels than people say it is. Within reason. I mean, keep out of the crown and don't bend the thing or rust it, for hunting and fun out to 300 you should be good. It's not a custom reamed carbon bartlein you need for sheep at 700y right?
Anyway, it's jsut a thought, it sounds like the fouling is chapping you a fair bit and that's understandable. If you don't want to sand the barrel that's understandable too. I appreciate the write up/review. Like I said before I've got some antique rifles that could really benefit from this and it's nice to know it's an option.
