I have to respectfully disagree on that recommendation. IMHO, if it takes more than 50 rds to "break it in", something's not right from the get go. Someone is cutting corners somewhere. For what the top builders charge, if it didn't shoot reliably with the first box, it goes back and keeps going back until they get it right.
The last wadgun I had built was delivered the day of one of our indoor Bullseye matches. I just picked it up and shot the match. Took nearly my first 2 slow fires to get it sighted in, but my 3rd slow fire for the NMC was a 98. It, like it's 2 predecessor's, has never had a gun related malfunction with anything from H&G 130's, H&G 68's, Lyman 460's, Zero SWC, Zero 185 JHP, Nostler 185 JHP, or 230 hardball. The first one he built for me has has nearly 85,000 rounds through it (now on it's 2nd barrel) with the same track record. All 3 are great shooters with exceptional triggers. The best one will do under 1 1/2" @ 50 yards (8 were sub 1" & had 2 fliers) and the worst one is at 2'' (it's also seen over 53k through the second barrel).
I just finished a double blind magazine test on 17 different magazines @ 50 yards out of the Ransom Rest. Found out the 2 I've been using for slow fire's are not the ones I should be using. That opens up a whole new arena for me to squander time & components on. Time much better spent dry firing.
Allen