Your mod. 60 should handle just about any ammo, including bulk. It's not from personal experience but I've not heard many good things about the Remington Bulk. The rest seem to work well most of the time. That may vary from one lot number to another. As far as accuracy, it's kind of a trial and error thing. Most every rifle has it's favorite. Most CCI ammo is good and my son favors the Wolf Match ammo when he's shooting in local competitions. I just shoot for fun so I usually buy the Federal Bulk. For more serious target practice, I use the CCI's. I have some Remington Match Ammo but I've not tried to group it yet.
Just follow the recommendations in your owners manual. They write those manuals for a reason.
i use quite a bit of the Remington bulk ammo in my M60 and also the Federal bulk ammo. the worst i have ever used is the Winchester bulk ammo. lots of bad primers and failing to fire, even in my other rimfire gun.
The CCI seems to be the most consistant that I've seen. The bulk ammo in Federal, which I have the most, is ok but seems to be a bit more iffy on the accuracy if you are really trying to nail every shot exact. If you need some speed go to the CCI Velocitor or Stingers. Just make sure you use the same target ammo that you use for hunting so they will land in the same spot.
I shoot a lot of .17hmr and I have to check lot numbers of varius ammo until I find one that is consistent, some batches are not so good. And then when I find a good lot number I buy as much as I think I need for the year. Sight the gun in one time and done for a while.
I have a model 60 that my father bought me in the late 70's. It has a micro groove barrel common to all Marlin's of this era. I have shot many different brands and velocities. I have spent several dollars trying to find "the" round that works. It stands to reason that the standard velocity "target loads" shot very well on paper but were less than stellar on squirrels. I was at a loss. I had tried stingers, velocitors you name it I fed it to my 60. It was very interesting. My 60 hated high velocity ammo. Stingers made a shotgun like pattern with no rhyme or reason. Such was true of all high velocity loads. Hyper velocity? forgetaboutit. I finally found that CCI SGB's shot best groups on paper and were murder on squirrels. Thet are not hollow points, which as I was tought was the only thing to fire at game, they are a flat point. They work very well....I wonder what others have found about ammo and there 60's?