P.S. the older verson was milled from a solid block of steel , newer ones not so . And UNDOUGHTLY SO WITH THE NEWER MODELS .Come and shoot mine !
Actually, the 740, 742, 7400 and 750 all have machined steel receivers...based on the 870 20 gauge. Most of the rifles in these families will function reliably if they're maintained and shot properly.
The chambers MUST be cleaned religiously. If you don't clean the chamber, it becomes corroded/rough and will undoubtedly cause extraction/chambering issues. This can be a problem on older/used rifles because they are hard to clean from breech to muzzle like you would on a 700...so people clean from muzzle to breach. As the brush hits the chamber, all the fouling/chemicals splatter against the chamber walls...and nobody cleans their chambers. The orifice hole might need to be cleaned out although it's not usually too much of a problem unless the orifice just happens to be drilled through a land in the rifling...then they tend to foul up a little quicker.
When I say they need to be shot properly, understand that even though these rifles are gas operated, they do require a little bit of recoil energy or inertia to start the action opening. If you don't shoulder the rifle properly and lean into the shot, it might not cycle like you'd want it to. Soft, squishy recoil pads can exacerbate the issue which is why these rifles either had a hard plastic butt plate or a solid rubber recoil pad.
Remington made some changes to the 750 to enhance the reliability. From what I understand, they're working pretty well (with the exception of some early magazine problems). So, if your budget allows, you might want to look at one of those.
If you're looking at an older used rifle, make sure you can get a gunsmith to put an eyeball on it...specifically checking the condition of the chamber, orifice hole, and action bar rails in the receiver. If it all looks good, you should have a great rifle on your hands that'll last you for years. If it's suspect, you'd probably be better off to leave it on the shelf and look for other options. Of course, like others have mentioned, a 7600 would give you fast repeat shot capability with fewer maintenance concerns...
Jason