breaking in a barrel, is EXACTLY like breaking in an engine. same concept. it mostly applies to rifles than pistols but you still break in a barrel regardless in my opinion. to do a barrel, ya just use the cheapest ammo you can, and what you do is, ya clean the crap out of the bore, after every shot, for about the first 20 rounds or so, and then youre good to go. basically, without going into a book here, is it smooths things out in there, so that A. its a lot smoother so now its more consistant shooting, B. its easier to clean, and C. it lasts a little longer.
it overall just works and shoots better now. Noone really notices a difference cuz 1, noone does it. 2. noone does it properly, or 3, noone cares enough to do it. Like i said, it mostly applies to rifles, and most people do it to rifle barrels, cuz it makes it a tad more consistant after. and thats what most picky target shooters want, is consistency. cuz, if youre off by a quarter inch at 75 metres, fine. but be off that much, and by the time that bullets out to say 700 metres, youre going to be off by a light year. so consistency is key with us anal rifle shooters.
pistol shooters dont really care enough to bed in a barrel cuz not only is accuracy down to +/- 2mm's not really a concern cuz of the short range, but pistol barrels are tougher by nature. the main benefit for an average pistol shooter are probably just an easier to clean barrel, which is reason enough for me to bed in a pistol barrel. (im really finicky about my weapons getting cleaned, from being in the military)
There's a lot of speculation about using lapping compound on your bullets when bedding it in, being the best and only way to do it, but many disagree. Its not that necesary on a pistol. super cleaning the barrel between each shot for about 20 rounds is bedding enough to be honest. Ya only gotta do it once, and I think its worth it. Its free, but costs a little time and elbow grease if youre willing to do it. Just use a NON METAL bore brush, (plastic, not brass, bronze or steel) attached to a ONE PIECE stiff cleaning rod, made of either graphite/carbonfiber, like those good golf clubs or arrows are, or aluminum, brass, or if its steel, make sure its rubber or plastic coated. No steel sectional rods. never. and get some hoppes or other brand name COPPER solvent rbc, (bore cleaner) and some patches, and clean the bore with the rbc, then run clean dry patches down it, till they come out clean and white. if you got your technique down, it should only take about 5 minutes per cleaning. it goes fast.