My own experience is limited. But the .22LR conversions that I have shot before, were always just a different bolt and magazine. The barrel stayed the same. No changes to the barrel, tolerances between .22LR and 5.56mm are not that different. Not the most accurate, but good for training the fundamentals of shooting principles cheaply. Or where there are restrictions with the backstop. Essentially, you have a blow back rim fire rifle.
This is not like a hand gun conversion.