What's reliability like for the older remingtons (740/7400 ect) and winchester model 100?
In Fench we call those the "Jamm-o-matique".
The Reminton 742 and 7400 are similar rifle with a different locking bolt arrangement. Both suffer from the same problem - the receiver recesses are made of relatively soft metal and get peened up by the bolt going in and out of battery under recoil.
I've seen new 7400's start to systematically jam after less then 200 factory rounds. when you disassemble, I know what I'll find before I see it - peened bolt lug recesses. There is no enduring fix. I've peend them back before, you get a few more boxes of ammo through the gun and it will start to jam again.
It's telling that most gunsmithing stores sell used 7400 and 742 guns with no warranty.
The Winchester 100's are notorious for ejection and extraction issues - the end result - jams. The yalso suffer from pistons that deteriorate and wear quickly compared to other designs. The 100's also had a serious recall to change firing pins. The pins most original guns shipped with brok easily and failed with the pin protruding - causing slam fires and runaway full-auto bursts.
Another Winchester 100 issue is that as the guns wear they develop slop in the dovetail on the front of the receiver. If the rear guard screw loosens under recoil, vibration, etc. , the rear of the trigger group drops down a little and the bolt will fail to #### the hammer on rearward travel. The bolt goes into battery followed by the now uncocked hammer and jams the gun to the point a full disassembly is required to rectify the jam.
So no, I would not consider either gun as serious contenders for "most reliable".