I've had the pleasure to shoot two different 336's and the best group i got from them was around 1 and 3/4 inches, i was using the 170 grains for that group, it seemed like those particular guns i shot liked the 150's better
Got 3 Marlin336 in 30-30 all shoot 1 inch or less with 5 ahots brom bags at 100 yards. They like the Remington Green/yellow Cor-loks.
Two of the rifles have refused to shoot the Leverlution ammo (4-5 inch groups) at 100 yds. I've not even tried Leverlution in the 3rd, as why mess with a great shooting rifle. These are guns were bought 2- in the 1970s, and one in the 1963. after all these years it is ammazing to see these groups at 100 yards.