Yes on the current made barrels, depends on when it was made for older barrels, if it has an extractor it's likely 1:9", but even that may not always hold true, best advice is if it was made between 2005 and 2007, check it with a cleaning rod if you want to be sure of what you're buying.
Fluted barrels were first offered in 1:9", then they switched back and forth, Superlight barrels were the last to be changed, they're not big sellers, so the run of 1:12" barrels lasted well into the 1:9" Marlin production timeline. H&R told us that ALL 223 production would be 1:9" starting in early 2006, but then they didn't follow thru for some reason, so 2006 and early 2007 up until Marlin started making them were mixed, and to top it off, even they couldn't tell you what the twist was by the serial number.
Tim
