I shot benchrest for years, broke in a lot of barrels. The break in process has a lot to deal with the condition of the throat, so you are lapping in the rough edges of the leader angle. With the Teslong bore scope and the Hawkeye bore scope, you can often see just how smooth or rough the leade angle is, and perhaps the bore condition.
I saw many barrels that broke in with less than 3-5 shots as they quit copper fouling.
I quit breaking in my custom barrels in 1987, I just go and shoot them. So, on my first outing, I figure 2-3 shots to get sighted in, then 10 two shot groups. A thorough cleaning, and inspection with the bore scope after the first 22-23 shots fired, usually indicates what kind of barrel I have on my hand. In the custom barrels, you can often be very effective in working up initial loads in 2 shot groups, where you are looking for the same bullet hole type of group. This 2 shot method will allow you to get a "good idea" where to look, save components and barrel wear.
With cartridges like the 25/06, I often worked up "best load" within 20 shots, MAX, and often within 12 shots. Often, velocity may increase within 100 shots and you may have to alter powder charge .5g. When you have several barrels with the same barrel maker, chamber reamed by the same reamer, more often than not, the barrels will shoot very close to the same load.
So, on my first outing with a new barrel, I will figure two shots to get zero'd, then start work load work up in two shot groups. You can assume that the action is bedded and the barrel is freefloated in a quality stock. I start with the bullet seated .020 off the lands most of the time, find the most accurate powder charge, then alter the seating depth, and finally alter primers. The whole process does not take long as I load at the rifle range. If I do not see the bug hole groups I am looking for, then I will change powders, go through the same process.
When you do find the best load, it is important to chronograph that load. As the throat wears, you will loose velocity, then you will have to add a touch more powder to get that velocity back where the barrel harmonics dumped the bullets opening up a bullet hole.
The Bore Scope and Chronograph with accurate records kept will give you very, very accurate loads with multiple powders and bullets.
I will add that Cut rifle barrels take a bit longer to break in than button rifle barrels, which I have owned, relating to very minor copper fouling in very fast cartridges.
Three of the very best things that any advanced reloader can purchase is a Wind flag, Teslong bore scope, and a chronograph, in that order.