If its a JM stamped 44 Mag, the oversized bore is common. You might have to go through a bunch of different type ammo until you find one that works.
Another anomaly with light 44 mags is the velocity is in the slow range but the recoil is substantial enough to move the gun before the bullet has left the barrel and will make accuracy almost impossible until you hold it down. The Ruger 77/44 is the worst offender of this freak scenario.
If its a Ruger made Marlin with the red dot in the stock, its either your scope, mounting, or the above problem, not the bore size.
PS, I’ve experimented with every 44 mag factory load, obscure loads, and many handloads on animals over the years. None of them outshine the others in actual results. The two I settled on were MagTech 44a 240gr JSP and the Remington 180gr. The Rem 180gr solves any velocity/recoil/movement issue because they clock about 2,200fps in a 20” barrel.
Last edited by JohnnyLoco; 10/05/23 07:22 AM.