Before Marlin closed, I was asked to do a test on 44Mag barrels to see if a faster twist (1:20") would perform better than 1:38"..............We had had a number of requests from the field for a 1:20" 44Mag..........
I had 12 barrels made with 1:20" rifling, and assembled into rifles.........
We then chose 6 from the 12, and shot them at 100 yards in controlled conditions against 6 selected 1:38" guns, using both jacketed and commercially cast lead ammo..........
As I recall, (I no longer have the data).............The Jacketed bullets shot the about same in both twists..That is to say, it was difficult to conclusively say the faster twist was beneficial to accuracy............
The cast bullets also shot pretty much the same...........As the cast bullets were commerciall loaded, and not sized to a particular barrel, we selected the two rifles in each twist rate that performed the best with cast ammo, and shot them with jacketed ammo............The results were so close that Marlin R&D decided to continue with the 1:38" twist in 44Mag rifles..............
I suspect, If someone has a 1:20" 44Mag barrel on their rifle, that may be one of the Original test rifles...........Those test rifle would be either late 2007, 2008 or possibley 2009 rifles..I can't recall exactly when the test was requested and the rifles were built. There was a lot going on at Marlin, then......
I recall CalvinMD wanted one of those rifles, and at the time, Marlin would not allow them to be sold, as they were non-standard rifles.
I lost track of those 12 rifles, but I'm about 100% sure they were finally sold by remington, as Marlin came closer to closing the North Haven doors.......
To summarize, I wouldn't care if my 44Mag rifle was 1:20 or 1:38.................
Tom