Marlin switched from the regular steel barrels of the M322 to the stainless steel barrel of the M422 (both Microgroove), presumably in response to complaints about short barrel life. In fact, the subject typically only arises when someone buys an older Sako, looks down the bore, then writes on a chat board "Hey! The Sako I just bought has a BUNCH of little lands and grooves in the barrel!" I've never come across any information as to why Sako used both the multi-groove and conventionally-rifled barrels contemporaneously nor why they dropped the multi-groove barrel. I've detected no difference in how either bore handles fouling or cleans up. 223 for extended periods (60-100 rounds without cleaning) during an afternoon of prairie dog shooting. Have you tried the foaming bore cleaners and if so what's your verdict? I know it's the lazy man's way of cleaning a barrel, but it seems to work really well for me. Recently, I've been using the foaming bore cleaner which I simply let sit for an hour or so, wipe it out, then foam it again and let it sit another 30 minutes or an hour before running several dry patches through it. Paulson: I've cleaned a lot of barrels in the last fifty years, but I've never been completely satisfied with the various methods I've used, whether it was with a mild abrasive bore paste, an aggressive solvent, or plain old Hoppe's jags, brushes, or whatever. The action screws are almost always only luke-tight and the barrels are almost always in need of attention. When I obtain a previously owned gun I always do two things before shooting: Check the action screws and clean the barrel (well, maybe also adjust the trigger if it is really heavy). Not to steal the thread, but paulson's suggestion to clean the barrel thoroughly is a good one. Clean the barrel at least every 10 shots during testing. With a little effort your rifle should be able to shoot sub MOA. Then I mount the scope I intend to use on the rifle. That 6X leupy is an excellent choice, but I usually mount a 12X to 20X scope during load development & accuracy testing, as it allows for more precise aiming. As stated, handloading will allow you to experiment with many different bullet/powder/primer combinations to develop an accurate load. If your crown is dinged it will never shoot well. This is another reason people give up on a perfectly good rifle. Now, clean the barrel again! Check the crown for any damage. Get a couple more different factory loads to see if your rifle has a preference.
Can't tell you how many rifles I bought cheap that the owner thought the barrel was shot out on that became tack drivers after a few hours of cleaning.
You would be shocked at how many gun owners don't even know how to properly clean a barrel. I have found that most of the accuracy problems with any used gun are related to a fouled bore. Relieve the wood contact on the barrel except at the tip & then clean the barrel using a good aggressive solvent & a bore brush.