remmington 7400 that doesn't chamber or extract

Typical of the 740-7400 series of Remington semi-autos!!

Yikes! Your going to depend on this rifle to save a life? I wouldn't take it in the field unless I had no other rifle. My worst experience in all my firearms to date happened to be one like yours only in 270. I purchased it around 1982 and the thing would not group no matter who worked on it. I finally gave it to a backyard gunsmith for hardly anything and he never could get it to do anything. My advise is to get rid of it and now. Unless your the fastest runner in the group.

A hamfisted smith could very well have crushed the reciever when he clamped it to get the barrel off. That would give you the bolt problems.

The stuck case would be an entirely different problem. Likliest cause of that would be rough and/or tight chamber.

btw, I agree with the others. You don't wanna go betting no lives on a Remington auto.