When you ask about the Remington Magnum, WHICH Remington Magnum, the budget Express or the high quality Wingmaster? ALL Remington's are Magnum models now.
Which Express, the Sporting model, or the Home Defense Model?
Re-read the above post where I list each version's features.
Basically, the cheaper Express models have a rougher finish, inside and out, rough black finishes, plastic parts, hardwood or synthetic stocks, can't accept a magazine extension UNLESS the mag tube is altered, and use some MIM parts.
The more expensive Wingmaster and Police models have much smoother finishes inside and out, have polished blue or military grade parkerized finishes, walnut or synthetic stocks, WILL take magazine extensions without alterations, and use NO MIM parts.
The Express models are "Budget" versions, made cheaper to compete with the cheaper to make Winchester and Mossberg guns.
The Wingmaster and Police are Top of the Line deluxe models.
As for durability, reliability, strength, and longevity, the Express models are about as good as the more expensive Wingmaster/Police guns.
The Express "possibly" COULD give some initial problems until broken in, and over the years and the rounds fired, the MIM extractor MIGHT give problems.
This is to be expected with a budget gun.