Too bad you don't reload. Marlin 44 mags have 0.4315" groove diameter barrels. Most " .44 caliber" bullets are 0.429- 0. 430" ... meaning they are undersized bullets. This is the reason poor accuracy is often an issue with Marlin 44 mag rifles.
I used to have a JM-stamped Marlin 1894 in 44 mag, with Ballard rifling. Accuracy was poor with 240 -265 grain jacketed bullets in the 0.429 - 0.430" range. I found Zero Bullets (through Roze Distribution) make a 240 grain jacketed bullet at 0.431" diameter. It shot well.
They are available as just bullets / components for reloading, not factory loaded.
If you reload cast bullets, you can find 0.432-0.434" diameter bullets- for Marlin 44 mag accuracy.
Not what you wanted to read, but factory 44 mag cartridges just simply have undersized bullets for Marlin 44 mag chambered rifles with their 0.4315" groove diameter barrels.
