There should be no problem with the 444 Marlin in the Contender.
A potentially dangerous statement without adding some qualification. Shooting 45,000 psi or lower factory 444 Marlin ammo is one thing, and folks have got away with it for years on their Contenders before developing a problem. But the 444 is easily capable of being loaded past what the Contender can stand up to, and has been too many times. Lots of varibles in reloading... which materials used, technique, not to mention your particualr chamber, the condition of your frame/barrel, headspacing, etc, and the list goes on and on. The 444 probably accounts for more Contender blow ups than any other cartridge (not fact, just personal observation from someone who has shot and reloaded for Contenders almost as long as anyone else has, and much longer than most). IOW, 9 out 10 that I saw or heard about were 444 Marlin Contenders.
A better pressure indicator than a sticky frame with the Contender IMO is the very earliest signs of the rimfire firing pin/bushing on the case head of the brass. You will often see that long before a frame becomes hard to open (positive proof that you have already pushed the load too far). Naturally the brass itself plays a roll in how much pressure it takes to imprint it. Regardless, I never understood folks pushing max (or over) loads in any firearm. Doesn't equate to diddly down range, not enough to take the chances.
It was implied above that there might also be a problem with the 444 Marlin in the Encore frame.
Implied by the barrel makers. I simply posted the facts of what they do and do not chamber now days with an assumption why. They must have a reason though, and I'm sure they have more knowledge than you or I to base that decision on.
I have looked in the reloading book and the 375 is listed for contender and the cup is a lot more than the 444 marlin...
Please don't be mislead by pressure ratings when comparing one cartridge to another - that too is a dangerous assumption. SAAMI, CIP, etc CUP, PSI, Strain, etc values are fine as far as they go (and rarely are interchangeable), but they are NOT the last word on what is and what is not safe in a Contender, particualrly your Contender. While the Contender was designed mainly for low pressure large case head and high pressure small case head cartridges, there are many ramifications involved that allow some others to be safe and some others not to be for Contenders. The ramifications of what the acceptable difference's are based on what makes them safe or not would take pages to discuss. So I'll just add that for the 444 verses the 375JDJ, the later could safely run higher pressures in a Contender due to it running at lower back-pressures as a default of its design. BTW, if I remember correctly JD once stated the 375JDJ was rated at 42,000 PSI in his Contender barrels. Long time ago though so the memory could be foggy. Regardless I never had presuure signs in any of the four 375JDJ barrels I had from the early 80's even shooting 270/300 grain bullets near or at the top of JD's loads for them, and the number of rounds fired between them had to be in the ten thousands because I shoot all of them often with a lot of rounds fired each time (ie, a typical range session with them was 200-300 rounds).
YMMV
