Your question will get a lot of the "experts" up in arms. It came up on an AR site a few years ago and I think someone would have been hurt if they had a enough bandwidth to send a fist or round over the internet.
PLEASE NOTE I AM NO LONGER A COMPETIVE SHOOTER AND THERE IS A REASON. EVEN IF THERE IS SOME BENIFIT TO BE HAD IN THE COMPETITIVE ENVIRONMENT I DOUBT IT IS WORTH THE TROUBLE OR WILL EVEN BE NOTIED IN A HUNTING BARREL. ESPECIALLY BIG SLOW MOVING BULLETS. Even IF I believed the whole process to be worthwhile there is no reason to do it on most of the rounds Marlins are chambered for, unless you are going to try to hit golfballs at 300 yards.
I have read all about how this is meant to remove copper fouling until the barrel is properly carboned up and then the copper fouling becomes less of a problem. That has never been my experience. I have never done it even when "required".
MY OPINION - Its not a MUST DO for any HUNTING gun even your Sako. If a barrel is so danity that it needs to be treated like that to shoot well, then forget it. I am not sure where it came from but I wonder if some guy sat arround and dreamed up this whole thing believing no one would be stupid enough to do it so the manufacturer could say you didn't break the barrrel in properly if it doesn't shoot to your expectations.
Unless you are a very serious high powered rifle bench shooter you are probably not going to know the difference and even then you won't on a large precentage of the barrels. I have four tack drivers that all came with instructions to break them in that manner. My 6.8 SPC barrel went on and I sighted in the scope with 5 rounds, the last three 1/2 MOA. 60 rounds later I pulled a bore snake through it and put it up for the season. And I only did that because I had it out in the rain. This year probably only fired 10-15 rounds through it but the last 4 were at 4 different DR pepper cans at 350 yards. 4 for 4 and I have yet to clean it again. 15 years a go I had a 22 rf rebarreled with a 1" bull the smith told me I "HAD" to do all that or the barrel would never shoot prperly. It still shoots one holes at 50 yards even though I probably shot 1000 rounds through it before I cleaned it the first time, and probably even haven't run a bore snake through it in at least 2 years. Dirty little secret burnt powder protects the steel. That has been my experience with every barrel where this process was "required". Would they have shot better for more rounds if I hadn't done it. MAYBE, BUT I WOULD HAVE NEVER KNOWN THE DIFFERENCE. ALL 4 of these guns shoot in the 1/2 to 1 MOA range without the breakin in and are used as hunting rifles. So maybe sometime when I want to shoot a deers nuts off at 600 yards I will lament that I didn't break in my barrels properly.
My personal opinion is that we were taught to clean our guns by guys that shot corrosive primers and they learned from guys that shot black powder. My experience is that the action is more suseptible to fouling related problems than the bore with modern primers and powders. I generally pull a bore snake through my hunting guns at the end of season and right before I go to the range before it opens. I never sit down and run rag after rag through the barrel and do that until I get it spotlessly clean, There is abosolutely no research that even suggests that is required. To the contrary I find that all of my long range rifles shoot better with a fouled bore.
I have an M1 with a heavily pitted dark bore that shoots 1-1/4" groups at 100 yards with the military peep and my pitiful old eyes. After about 60 rounds you can spend hours and hours trying to remove all the copper fouling, but it still just keeps right on shooting those 1-1/4" groups. I bought it from a guy for $200 because he figured it had to have a new barrel to shoot up to his standards. I fired it when I first got it and it wouldn't hold a foot at one hundred yards. After I bedded the action, cleared the op rod, free floated the barrel and did the front handgaurd work I got quite a surprise. Most accurracy issues are not bore related. If I were going to compete with it I would rebarrel, but I still wouldn't follow the breakin procedure.