I have tried CCI, Winchester, Federal, Aguila, Hornady, Amscor, and Fiocchi.I don’t have a clue about what type or grain ammo to start with. Any suggestions?
Both of my Marlin .22WMR rifles prefer CCI 40g TMJ ammo. The Fiocchi 40g TMJ, which I believe is made by CCI, usually comes in a close second.
For comparison, my CZ 455 Varmint .22 WMR, prefers the Winchester 40g Hollow Pt. ammo, and the Hornady 30g V-Max.
Every rifle is different, so you have to test as many types of ammo you can find to see what your rifle likes. This was a challenge for the last few years, with the ammo "shortages" making finding any kind ammo a real pain, but the supply and variety of ammo seems to be getting a lot better now.
I have a .22LR Glenfield 25 that I thought was a turkey until I found the right ammo for it. The only ammo that shot with any accuracy was SK Standard +. I had tried 21 different brands and types of ammo in it before I finally found what it liked.
Just because one Marlin likes a particular type of ammo, doesn't mean that the next Marlin will like the same thing. EVERY rifle is different and will have its own preferences. This is the "fun" of owning a new rifle, finding out what it likes.
Over the next month or so, I get to try 21 different types of ammo in the Golden 39A I just got earlier this month.