APPROX. HOW MANY ROUNDS BEFORE YOU CONSIDER A NEW BARREL BROKE IN.....THAT IT SHOOTS BEST

Every barrel is different. Some take a box of conicals - some take 100+ rounds. Some shoot accurately right out-of-the new box. Inspect patches and/or plastic sabots for damage.

I have several barrels that have shot extremely well from day 1, a .45 and a .50 by Bill Large, a .58 by Green River Rifle Works, and a .73 by Riley Smith of Long Hammock Barrels.

Then, I have a .45 w/1-22" twist from Navy Arms that has never shot worth two hoots, and never will.

A good custom barrel by one of the well-known makers comes from the shop "broke in". No telling what has to be done to get a typical production-line ML barrel shooting well......

I agree with the others. But to answer your question with a number I think that 50 rounds is considered the norm for break in.

It depends on how polished it is to start with and whether or not you have a burr proplem.All so on whether it is a cut ,button rifled [there were some forign barrels that were forged years ago] or invesment cast.
There is also the fact that sabots do not preform the funtion of
"breaking in" a new barrel.
If a barrel has very much burrs or is seriously lacking in polish"firelapping" is often the best answer for that.
If it is a "normal" barrel 35 to 50 rounds with PRB with JB borepaste rubed into the patches will do it.
Some people prefer to use bore sized lead bullets,with polishing compound or even with out.
First run a cotten ball down the barrel if it snags off bit of cotten you have burrs.
second try some loads see if it acts like it wants to group if it does stay with it, it is best not to do any type of lapping or breakin unless it is needed.Lee

I always run a full package of powerbelts or pure lead conicals through a bore before I start shooting for accuracy. I don't know how much it helps but it certainly doesn't hurt. At the very least it helps me become a little more familiar with a rifle.