From the Marlin Firearms web site:
14. Q) Why has Marlin changed its rifling on Models 1894S, 1894CS and 1895SS from Micro-Groove® to Ballard-type cut rifling?
A) To accommodate the use of cast lead bullets.(Jacketed bullets will still function reliably.)
GunWeek:
In the mid-1970s, Marlin saw an upswing in shooter interest in old style guns. This was a time when European replicas started to cross the pond to a willing US market. Why not cash in on the fad? Bring the 1895 back in .45/70 and add the then new .444 Marlin? By then, Marlin had their newly designed rifling system called Micro-Groove. Micro-Groove was expected to bring new accuracy to the 100-year-old .45/70. If you are going to use only jacketed bullets, Micro-Groove really is an improved system. But those of us who like the .45/70 know that the only way to get better performance is to handload, and the best bullets are cast bullets. Much to our dismay, cast bullets didn't function too well in the new Micro-Groove barrels. Reloaders brought this to the attention of management at Marlin.
One of the reasons Marlin is so successful is that they listen to the market. Because of the comments by handloaders, the early 1990s saw Marlin going back to the old deep Ballard-type rifling. Several outdoor writers were invited to try the new/old Marlin. Randy Garrett provided his hard cast super bullets. It was soon obvious to the writers who were at the shoot that the teaming of these two new products was a home run.
enough said.
Note that there is a lot of information on the .444 Marlin rifle and cartridge. This is a microgroove barrel.
No it's not! But it used to be.
Again from the Marlin Website;
Caliber 444 Marlin
Capacity 5-shot tubular magazine
Action Lever action; side ejection; solid top receiver; deeply blued metal surfaces; hammer block safety.
Stock American black walnut pistol grip stock with fluted comb; cut checkering; rubber rifle butt pad; tough Mar-Shield® finish; swivel studs.
Barrel 22" with deep-cut Ballard-type rifling (6 grooves).
Twist Rate 1:20" r.h.
Sights Adjustable semi-buckhorn folding rear, ramp front sight with brass bead and Wide-Scanâ„¢ hood. Solid top receiver tapped for scope mount; offset hammer spur (right or left hand) for scope use.
Overall Length 40.5"
Weight 7.5 lbs.