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I hesitate to bring this up as I have heard so many pros and cons. But, if anyone would care to chime in on this the input would be appreciated.
I have a Match Grade Machine barrel in 35 Whelen for my Encore ProHunter. This barrel came with instructions for an extensive break in procedure. Wanting to be able to give an honest answer if the barrel did not shoot well and was asked about the break in procedure, I followed instructions to the letter. It required 75 rounds in total with cleaning after so many rounds which varied with the total number fired. This barrel is a fantastic shooter.
I have another barrel coming in next week from Match Grade Machine in 308 Win. I am sure it is going to come with the same brake in recommendation. I fully intend to follow their instructions this time, also. If nothing else it is a great excuse for range time.
I have never followed a particular break in procedure before getting my first MGM barrel. If a rifle shot well out of the box I never gave it a second thought. I have, when confronted with a new rifle that was stubborn out of the box, used a repetitive process of shooting and cleaning that turned the gun into a decent shooter. But nothing as protracted as 75 rounds. I fully believe that MGM would not insist upon this break in procedure just for the heck of it. Again, I will follow their instructions regardless. But, anyone have any thoughts on the matter of breaking in a barrel.
The first time I heard of breaking in a barrel was when I came to Colorado in 2012. It all depends on the manufacturer's post rifling cut attention to finishing whether it is a necessary process or not - or the user expectations. No rifle or barrel made in Europe or South Africa will sell if any amount of "breaking in" is required. If it becomes known that any rifle brand or new barrel is not capable of better than 1 MOA groups off the shelf other users here will simply stay away from that brand and buy something else.
"Breaking in" a barrel has different meanings for different folks even in the USA, but in principle it is to relieve the metal stresses caused by the boring, rifling and outside machining processes. International manufacturers like SAKO, CZ, Musgrave, Truvello, and others do proper stress relieving heating and cooling prior to final assembly.
No barrel from the above manufacturers will ever need lapping or polishing to ensure a smooth bore either - they all are mirror smooth from the factory. Any hammer forged barrel that in any case needs lapping or polishing after the process in any way means that a rough and ready mandrel had been used. Even hammer forged barrels need stress relieving.
Should a barrel need stress relieving it is best to follow the manufacturer's guidelines. There however is an old Boer method used by international 100-1000 yds event winners after a new barrel or rifle was bought: Two packets of ammunition (40 rds) was put through it at the best rate the shooter could load and fire it. Then it was allowed to cool completely, cleaned and only shot again the following day.