I don't quite understand what it means to break in a barrel. I've seen quite a few threads asking if it is neccessary or not to break-in a new barrel, but I don't get what that means. Any info or links to an answer would be greatly apreciated.

Chrome lined barrels dont need it,unlined does.By breaking it in it just means your wearing in the barrel slowly on its lands and grooves and chamber so it slowly gets used to rounds being chambered,bullets spinning along the grooves,bolt lugs to extension lugs.Sharp ends rounding or smootheing out for slicker and smoother operation.Parts mating to eachother..hammer to trigger etc.Some barrels need to be broken in like operating parts do on a new fire arm so it works flawless nothing to hang it up.On a new AR just the parts need to break in not the barrel the 100 rounds through it just polishes it out on a chrome lined barrel,the smae I guess on regualr steel just chrome is harder and dosent wear as fast.

Quoted: Chrome lined barrels dont need it,unlined does.By breaking it in it just means your wearing in the barrel slowly on its lands and grooves and chamber so it slowly gets used to rounds being chambered,bullets spinning along the grooves,bolt lugs to extension lugs.Sharp ends rounding or smootheing out for slicker and smoother operation.Parts mating to eachother..hammer to trigger etc.Some barrels need to be broken in like operating parts do on a new fire arm so it works flawless nothing to hang it up.On a new AR just the parts need to break in not the barrel the 100 rounds through it just polishes it out on a chrome lined barrel,the smae I guess on regualr steel just chrome is harder and dosent wear as fast.

Not necessarily, read here.

I tested a pair of Pac-Nor super match stainless barrels chambered in 20 Tactical awhile back.  Both had 25" .935" diameter barrels.  One was broken in by shooting and cleaning a bunch of times, while the other one was just fired without any cleaning.   After about 250 rounds through each one, I cleaned them both and sat down and fired some groups.  Both barrels were putting 5 shots into 3/8" at 100 yards.

I have noted in previous tests with all of the small bore Pac-Nor barrels, that the group size continually shrinks as more shots go down the new bore.  They usually start out shooting about 3/4" and slowly tighten to 3/8" after 200 or so rounds.  But it does not seem to matter if you clean between every few shots or not.

LonghornAR,
I have been using the barrel break-in procedure the mattld linked you above.  Essentially, it is a simple and rough outline of how Mike Rock breaks-in barrels and why.  I’m sure you’ve heard Mike’s name dropped every now and then on the internet in association with barrel making – and rightly so.  He is an extremely smart guy who has forgotten more about barrels than most will ever know.  Like you, I have noticed that there are as many schools of thought about break-in procedures or no break in procedures, for that matter, than one can count.  Personally, I tend to differ to individuals who have the experience and knowledge when I encounter a subject where I have a technical question.

I have been using the Smooth-Kote and BP-2000 products from Sentry Solutions for quite some time - 3 barrels that I still own.  I have been very please with the results and longevity of the accuracy in those barrels.  I have also been impressed with the ease of cleaning, lack of fouling, and copper deposits.  I strongly recommend them and have no affiliation with their company.  I do, however, have a strong affiliation with my wallet and don’t like having to pay for new barrels when accuracy drops off.  If you do choose to use the Sentry Solutions products, the small bottle of Smooth-Kote goes a long way.  The small bottle of BP-2000 dry lube gets eaten up pretty fast.  I have also found uses for it other than barrel break-in, so I use considerably more often.

Again, the link that mattld sent you is a good outline, but unfortunately the posting that made its way to ar15.com in that link leaves out something that I think is very important.  One key element that should be added, if you expect have an accurate setup that lasts: spend the money and buy a good hand-lapped barrel from the beginning.

Additionally, it has been my experience that using cleaning rods (or anything that passes through the barrel) made from a softer metal than the barrel material (aluminum, brass, bronze, etc.) with a bore guide will save your bore from being damaged more than anything else.  And keep these items clean, too.  No matter what barrel break-in procedure that you choose to use (or not use), it will not save your barrel from having your lands ground on by a sand-coated USGI steel cleaning rod.

I understand that there are many different opinions about barrel break-in and, there will undoubtedly be those who disagree with my opinion and practices.  This is merely what has worked for me at the suggestion of others.  I don't intend to offend anyone, just my two cents and the subject.

Mike Rock is currently turning a custom barrel for me.  I plan to rehash his suggested moly treatment again with him when I go to pick it up.  If there are any additional details, I will certainly post them.

BertR

I stopped breaking in my barrels when my friend bought the same gun as me, shot it like crazy, and it still shot just as good as the one i had babied trying to break it in.  Did I make the right choice?  I don't know, but all of my firearms shoot great, so I'm not going to worry.  Barrels are cheap anyways...

im not going to break in my next rifle