MP-44, if your have a Remington Model 12CS then it would be chambered in .22 Remington Special. The only difference between the .22 Remington Special caliber and the .22 Winchester Rimfire(WRF) was the type of bullet used. Remington used a round-nosed bullet while Winchester used a flat-nosed bullet.
But, if you have a Remington Model 12A or 12C it will be chambered for .22S, L or LR. The Model 12B is chambered in .22 Short only.
If yours is a Model 12CS and it won't chamber the .22 WRF cartridges properly you might want to take it to your favorite gunsmith to see if he or she can help you determine what might be causing a problem. Hope this helps!
Steve Mace