Musketman seez; "Any barrel will benefit from lapping"... and I say he couldn't be more right.
I have improved accuracy, and made for easier loading in all my guns by hand lapping the bore using a compound from LBT (Lead Bullet Technologies)......It is a compound of about 800/1000 grit that is used by a lot of professionals who normally charge two hours labor for this same job.
I'm told a good valve grinding compound, as sold by NAPA will do just as well at about one half the price of LBT Bore Lap.
Years back...during the age of Prodigy on the computers, I querried this question and got a ton of responses on the how's & why's of doing this.
Now, ten years and many rifle barrels later, I have come to the conclusion that there is no witch craft involved at all.
A very tight patch, mineral oil, and a compound no courser that 600 grit will do a fine job. You can do it by hand, or you can use a drill. I would suspect a drill, at it's slowest speed, would make short work of this job although I prefer to hand lap it with a rod.
On a "brand new barrel", I use 0000 steel wool with Old Dutch Cleanser to start this process....You will never believe what comes out of a brand new barrel until you see it for your self!
Wrap a .30 cal wire brush with 0000 until it's a tight fit to the muzzleloader bore , pour on the mineral oil, cover it with Old Dutch until it's a paste, and do about 100/200 passes through the barrel....you have to see it to believe it!
The thought that a new barrel must be "shot-in"...requiring up to 100 loaded rounds to "settle" the barrel...is all pure nonsense. Remove what the factory left behind, and the barrel will shoot just fine.
This same process can be used to "restore accuracy" if a build up of any kind has taken place. I did this to one of my Hawken's....not because of build up, but because I wanted to start / try a new process for lubing (new to me) that was suggested by Roundball here on the forum.
Does this "wear" the barrel? I suspect it does, at least some. After all, it is a not so mild abrasive.
Does it matter? After ten years of doing this, all I see is continous improvement on some, and nothing has gone south on me.
Use your head when doing this. Don't intentionally try to remove metal....just polish the barrel, over & over & over.
You'll like the results.
BTW; I'm told by those "who feel they know" to not use Ajax Cleanser, so I never have. (Don't ask! I don't know why not.)
I do know that Old Dutch and Rottenstone work just fine. LBT is probably the best, but pretty expensive. NAPA, and Craftsman both provide a Valve Laping Compound that works just fine...and you may even have something better.
Russ