Micro-Groove rifling, when combined with the proper bullet, is devestatingly accurate. A standard Marlin .22lr with a Micro-groove barrel is just as accurate (if not more) as any bull-barrel out there. The fun part is shooting every type of ammo out there to find out which bullet works best. Once you find the proper combination, sub-moa groups are a regular occurance.
What is difficult for many is finding the patience to find out which ammo works best...because using too skinny a bullet results in wild groups. One has to shoot thru a whole box of ammo to test it...recording the results as they go. I went thru 12 different boxes of 100 rounds over several days on each of my Marlins...I do the same with the other rifles/pistols as well...to find the BEST combination of weapon and round. Absolutely NONE of them like Remington Golden bulk or Federal bulk ammo.
Using the written information and micrometer readings, I then formulate my reloads for centerfire weapons, and buy cases of the favored rimfire ammo for the rimfires
What makes the Micro-Groove rifling work is simply that there are more lands & grooves (16 grooves) to grip the bullet as it passes thru the barrel. MCG also causes less bullet distortion/bullet jacket distortion and a better Gas seal
which gives greater accuracy.
Now oddly, I was playing around with my Model 99-G this weekend, which was pre-Micro-Groove...and shot predominately quarter-sized groups at 25 yards & quite a few dime & cloverleaf groups using CCI ammo & a Tasco 3x9 scope. Even started a smiley-face group at one point...
Being a precise shooter helps, no matter what the weapon.
After owning quite a few Marlins, Remingtons, Rugers, Winchesters, a Savage, a Squires-Bingham Model 16 (Armscor 1600 now) and Calico M-100 & M110 .22's...Marlin has far & away come out the winner of the .22LR accuracy race (also the .22WMR). Ruger I consider to be ONE step above a Savage in accuracy...but just barely, and only IF you set it up right...I also consider Ruger to be BELOW Savage in reliability. I can outshoot the Ruger's & Savage with my Calico M-100 all day long, and Calico isn't really known for their accuracy, just their high capacity. I do believe that mating the proper ammo to the proper weapon is extremely important.
I also HATE to replace parts on a new gun...Ruger's been peeving me off for a long time, starting with their Vaquero. Lousiest trigger in the business. Heck, Ruger's FAMOUS for lousy triggers in just about everything they've ever put out. The standard process on a New Ruger (pistol or rifle) is to Fix the trigger, tune the action, and replace all the springs after you get it home. That's kinda sad, but I do the same thing to old pre-1990 Taurus revolvers...at least they have the excuse of being OLD. Being forced to work on a brand new gun just isn't what I have in mind...I prefer to take it out of the box, sight it in, find it's favorite ammo, and enjoy.
The only thing that I consider even close to a Marlin for .22lr accuracy & reliability are the CZ's. They'll give you a run for your money...but at half the price, Marlin wins that race as well. Absolutely nothing I like better than outshooting a CZ owner and having them wander over to see what I was using...shocks the heck out of them