My 1894, 44 mag will hold 10 in the tube. It may be with the spitzer bullets, the additional length of the bullets is not allowing that 10th. Check the overall length of the LeveRevolution rounds against the overall length of FN rounds. I bet there's a little difference, at least enough to make up the half round.
this is what I found on the marlin website as per specifications for the 1894. I did not see a copyright, but if its not OK to show this, I apologize in advance GB. Don't want to cause any problems for anyone.
Caliber 44 Rem. Magnum / 44 S&W Special Order Online from Gallery of Guns
Capacity 10-shot tubular magazine
Action Lever action with squared finger lever; side ejection; stainless steel receiver, barrel, lever, trigger guard plate, magazine tube and loading gate. Hammer block safety.
Stock Straight-grip American black walnut; cut checkering; rubber rifle butt pad; tough Mar-Shield® finish; nickel-plated steel fore-end cap; swivel studs.
Barrel 20" with deep-cut Ballard-type rifling (6 grooves).
Twist Rate 1:38" r.h.
Sights Adjustable semi-buckhorn folding rear, ramp front sight with brass bead and Wide-Scan™ hood. Solid top receiver tapped for scope mount; offset hammer spur (right or left hand) for scope use.
Overall Length 37.5"
Weight 6 lbs.