RE: What's wrong with my gun????
No experience with the 7400 but my first firearm was a Remington 552 speedmaster .22. I was getting one for Christmas, pored over all the catalogs, decided on a Marlin bolt with a tubular magazine, went to the store and it was out of stock. The guy sold us the Remington.
That gun jammed on a VERY regular basis from day one. If I knew then what I know now, I would have taken it back immediately. I kept it, put up with it, did a bit of home gunsmithing in my later years, and finally took it to a 'smith. It came back and hasn't jammed since, years of good service.
I can't say I'd buy another Remington semi-auto rifle. Love their shotguns, just not the semi-auto rifles.