RE: Remington 7400 in .308 Problem
These rifles are just fine as long as you follow the manual. Don't know about present rifles, but back in the late 50's and at least through the mid 70's, Remington shipped a bronze bristle chamber brush with each rifle. Normal cleaning, followed by a good chamber brushing, took care of any problems. We did not leave but just a tad of oil in the chamber for rust preventative.
I hunted for years with a 742 in 6mm, my father-in-law hunted with a carbine (18" bbl) 740 in 280 Rem. We shot these a lot at the range, too, developing handloads that delivered 3-shot 1.5 inch groups at 100 yds. LOTS of shooting. I have NEVER had a jam. Never.
PS - Old IMR 4320 was the best powder for both of these rifles.