The first thing I do when buying a new rifle is to round the top of the lands. All my new rifles have rounded lands at the muzzle. However, one has to differentiate rounding off the lands and coning the muzzle. I round off the lands by charging a one size too large for the gun caliber lead ball with a grinding paste, putting a wood screw into that lead ball so I can chuck it into a cordless electric drill. Then rotate the lead "lap" to achieve desired angle around the circumference of the muzzle. Sometimes if I detect any sharpness withy finger I'll take a very fine auto-pain sand paper (2000 grit) and wrap it around my finger to just break the remaining edges. How well this works you can see below. This is the right barrel of the set in question.

Then there is coning. That is a completely different treatment. I have two (bought used) guns with coned muzzles. Both have rifling opened up at the muzzle with a gentle slope in the first inch or two. I like how those guns load, but I haven't had a need to do that to any of my new guns. This is how a "coned" muzzle looks like. (yes it is a rifle and it shoots great - you can't even see the rifling it is coned so much).

Then there is everything inbetween those two.

As for lead I buy all my lead as "technologically pure" (next grade is analytically pure - you don't want to find out the price of that grade :-). I measure every batch with a fairly crude Lee hardness tester which shows me a 100 thou impression that translates to bhn of 5~6. That's soft enough for all my other rifles.

You are of course free to think that, but I'll point out once more I've tested all ball sizes I had available (562,570, 575) with all patch thicknesses I could get to load(8,10,15,23) with all loads. I went through a 1.5kg of powder in a week and following that I chose the ball/patch combo I like the most. Tighter combinations didn't shoot any better.

Now that I think of it. It is not uncommon at all in black powder muzzleloader shooting to use soft lead undersized projectiles. For example I have a Pedersoli "Hawken" 50 cal with a fast twist barrel. It shoots best with a heavy conical Pedersoli bullet made for it sized (with their hand sizer) to .503. It is so under size that is practically slides down the ( clean) bore with just the weight of the fiberglass ramrod on top.

At the other end of the scale is my "squirrel gun". The muzzleloader I show the coned muzzle of. It is a Pedersoli Plainsman .38 cal. made in 1970s. It shoots best with a 375 ball and 12 thou patch. That combination loads with (heavy) hand pressure into the muzzle coned to bore diameter.

If you don't have to use any impacts to load that ball/patch combo you must have a coned muzzle. A 562 ball with a 21 thou patch will have a 0.604 diameter. For this combination to load with a press of a short starter you would have to have rifling 12 thou deep that you ground off entirely just as I show in my coned muzzleloader. Is this how your muzzle was?

I had no need to cone the muzzle in the Kodiak as it shot (per barrel) holes touching at 50m with the right load.

Would it shot well with 120 grain load if I coned the muzzle and used even thicker ball/patch combo? Maybe? Who knows. The problem is that it is a set of short barrels. 24 inches by the book. In reality 23.3 inch. Minus an inch for the breech plugs it is 22.3 inches. With such short barrels I'm reluctant to make any irreversible changes to the last inch or two of the barrel.

Now coming back to the subject of regulation. Having found no detailed information on the subject I looked at various videos and pictures of commercially made double rifles by well known makers. Judging by how muzzles look compared with breeches the regulation looks a lot wider than what Pedersoli does. Currently I'm leaning towards soldering the barrels with soft solder (so I can de solder repeatedly without causing any further high heat stress) for the barrels to "cross" at 50m and test. Then adjust from there.

As for straightening those barrels the pins I made to check straightness slide nicely through the entire length of both barrels. I think they would certainly bind if there was an internal bend. Therefore the bores must be true and what I thought were bends are just inaccuracies in turning the OD they did at the factory. Good.