Interesting read, sort of.
As for his accuracy problem, it may be due to the interesting dilemma posed by the 44 mag cartridge. There are DIFFERENT SAAMI specs for pistol vs rifle; something that does not occur with other pistol calibers. The SAAMI spec. for .44 Magnum rifles is .431, while the SAAMI spec. for .44 Magnum handguns is .429" diameter. As for why this discrepancy,
I found this post by a W.R. Buchanan from 2017 on the Cast Bullets forum;
"OK Rem/Marlin is not going to change to .429 bores because the SAMMI Spec for .44 Magnum rifles is .431 +/- .002. The larger dia. is due to the rifles inability to vent gasses like a Revolver does and thus the safety margin for pressure is much less. Factory .44 Mag ammo is loaded to 36,000 psi and the 1894 action is good to about 45,000psi ( actually 43,500) so there is not much room for customer error. Thus the larger bore dia. to cut pressure back. No manufacturer builds guns to be fired with Handloads. They can't control you or yours so all guns are designed and produced to be safe with Factory Ammo."