What you heard about oversized in Marlins is correct.
I owned a 44 Mag M1894 since the early 80's. This had a microgroove barrel and was not very accurate. You could push a patch in the microgroove barrel and feel tight spots as you went to the muzzle. I am not impressed with the quality of microgroove barrels. I think the best use for them is to support tomatoes in the garden. In 1999 I found out that Marlin was making new “Ballard” barrels. I called up the factory and discussed replacing the microgroove barrel with a Ballard barrel. The gentleman at the factory told me that it would cost $130.00 to get this rifle rebarreled. When I mentioned that I was firing .429 cast bullets, the gunsmith informed me that the rifle barrels were made to SAAMI specs which called out for rifles a barrel interior dimension of .431”. Marlin claimed that their specifications for the barrels were 0.431 +- .001”.
Marlin had not changed the 1:38” twist from the microgroove barrels nor was the groove depth significantly deeper than the microgroove barrel. In my opinion the difference between a Ballard barrel and a microgroove is a reduction in a bunch of lands. This is a mistake in my opinion as my Ruger pistol barrels had much quicker barrel twists and were much deeper grooved, and shoot cast bullets very well. The Marlin twist works with 240's, but not with my 290 LSWC's.
The factory guys were very positive about the quality of these late 90’s era barrels. I asked the gunsmith to find me a good barrel made to the minimum dimension because cast bullets are sized .429". The gun smith air gaged a number of barrels and claimed that none were on the low end, I got the basic understanding that the barrels were all .431 with very little dimensional variation. Even though that was not what I wanted, it shows that production processes had improved in 18 years.
The Ballard barrel shot my cast bullets better than the microgroove, jacketed bullets shot reasonable . About what you can expect is 4 inch or less groups at 100 yards.
Still, after examining the long and tedious take down instructions on Winchester M1892's, the Marlin is the only way to go.