My brother's 452 American shoot about half of its 3 shot groups under MOA @100 yards with Federal American Eagle. Match ammo shoots about the same in that rifle and is more $.
I use my 452 trainer with open sights but have gotten 2-3 inches @100 yards and the rifle can do better.
The only 39a I have shot does similar to my trainer with open sights so I would assume my shooting is the limiting factor. I think this rifle could use a scope to really test the accuracy.
A side note: nether of the cz rifles will group CCI CB longs so the Marlin 39 has an advantage there.