I only shoot factory guns because I don't own any custom guns.I have tried the break in but don't know if it worked because I don't know how it would shoot if I hadn't have did the break in.But if it works for you I would do it.
This is what I have done the last few years when I get a new gun .I use JB and work it at least 200 strokes and it gets it pretty clean.And so far it has worked pretty good for me because the guns shoot pretty good.Use this same method on muzzleloaders also.
If I bought a high priced barrel and they reckomended a break in method,would I do it ? you right I would custom barrels cost a lot of money and I would want to follow their instructions to the letter.I have been shooting since the 1940's but I am sure the barrel manufactors know more about their barrels than I do.So I would take their word for it.
If any of you want a very strong cleaner try some of the new 50 BMG from Montana.I have been trying it this past month and it sure does clean and fast.