I don't believe it is inherently more accurate than other actions, including but not limited to other Marlins, just a bit stronger than most because of the high-pressure cartridge it employs.
Sigh, this is what I meant about Marlin doing a p*** poor PR job.
Changes made to the Marlin Express series from previous tube fed lever guns:
1. Receiver to barrel mating surface machined to higher tolerances giving greater contact surface
2. Barrel threads machined for tighter fit. I've heard that marlin went from square threads to V threads, but waiting to confirm this
3. Magazine tube to barrel attachment completely different from any other tube fed lever gun, including other marlins. You can't tell this by looking at it though.
4. Mag tube to receiver mating improved.
The mag tube mounting was changed to reduce the effect of the mag tube on the barrel as
a. it's weight changes as cartridges are fired and
b. drastically reduces interplay between the barrel and tube as the barrel heats up and only one side of the mag tube gets hotter due to it's proximty to the barrel. The uneven heating on the mag tube no longer places near the stress on the barrel older methods of attachment allowed.
The improved barrel / receiver mating makes the rifle much less susceptible to POI shift as the barrel gets hotter.
There are supposedly a couple more changes Marlin hints at but gives no details on. All of these changes are geared towards ACCURACY improvements, not strengthening the action. In fact, the 338 action is not stronger than any other Marlin action and is still rated at 46,00 0psi. Hornady / Hodgdon's magic powder allowed this achievement.
I've even had an e-mail discussion with the guy who was the head gun smith at marlin before they closed shop and he says these rifles are inherently more accurate than any lever gun marlin has made in the past.
This is why I made my statement, and experience by most owners has proven this to be true.
Just too bad the PR is so bad that you can't easily find this info.