I used to have a Remington 742 carbine (18" bbl) in 308 Win. Didn't shoot it much, but it would group about 2.0 - 2.5" @100 yards. It was 100% reliable. The only reason I sold it was due to it being a true original carbine model, it was a bit more desireable. A guy at the range made me "an offer I couldn't refuse." It was in great shape, and he really wanted it. I was happy to help him out.
The reason Rem 740/742 rifles get the reputation for "jam-o-matic" is that their owners don't clean them properly.
People clean them from the muzzle with a patch, maybe a bore diameter bronze brush. THIS DOES NOT CLEAN THE CHAMBER!
The reason they jam is due to fired cases sticking to dirty chamber walls (which never get cleaned when you clean the barrel from the muzzle. The ported gas for bolt cycling doesn't have enough force to extract the fired case stuck to a dirty chamber walls, and a jam occurs.
The pump version (Rem 760 /7600) get dirty chambers too, but the shooter can apply more force with the pump's action to cycle the action to eject the fired case.
The solution? CLEAN THE CHAMBER!
Use a brass/bronze 20 gauge bore brush on a short plastic-coated cable "cleaning rod". Use a bore solvent of choice on the 20 gauge brush. Attach the cable to a variable speed drill, lock open the bolt, and insert the soaked 20 gauge bore brush into the chamber and start "drilling clean" the chamber thoroughly. Then clean with large patches to remove gunk. Lightly lube the chamber ( example Marvel Mystery Oil).
examples of a a flexible cleaning cable:
https://www.amazon.com/Otis-Technology-Memory-Flex-Cleaning-Cable/dp/B00D1X00DK/ref=sr_1_32?keywords=flexible%2Bgun%2Bcleaning%2Brod&qid=1563021012&s=gateway&sr=8-32&th=1&psc=1
https://www.amazon.com/Flexible-Thr...mp;psc=1&refRID=PQ80EW8YAGC7R0VTYNVRYou will need an adapter tip to use the larger diameter shotgun bore brush, on the smaller "rifle/pistol" size female thread on the cable.
Keep the chamber CLEAN, and lightly lubed, and you won't have jams.
Use Ballistol spray gun cleaner in the action internals. Toothbrush clean it, and respray the action. Learn how to remove the trigger group and clean that too.
Your Rem 742 is a fine rifle. Keep the chamber clean, and enjoy it. It is a fun gun to shoot.
