I think I would have called Remington directly when you first noticed the malfunction and sent the gun to them for repair or replacement. It doesn't sound like the local gunsmith got things reassembled right. Given a recall situation, I don't think I would have taken the gun apart myself at that point, although I understand your frustration for sure...

I have an old Remington Model 14 pump rifle that was my grandfathers. At one point my uncle had it in his gun case and I asked him if I could have it and if my grandfather hunted much with it. He said that he used to hunt with it, but there was something wrong with it, but he didn't know. So I inspected the barrel and cleaned/lubed it, and picked up some ammo for it.

Went out to a field where I had set up a target about 30 yards away, and a buddy of mine was standing to my left and slightly behind me... I'm right handed, so as I pumped the first round into the gun, the barrel was pointed up and about 45 degrees between him and where I was facing... racked the slide forward and BBBBOOOOOOOMMMMMM!!!!

Scared the crap out of both of us!!!!

I was thinking stuck firing pin, but on inspecting the bolt face, the pin was not sticking out. I put a drop of gun oil into the firing pin hole, and ran the action several times... put in another round, holding the gun pointing down toward the ground a few feet in front of us... KABOOOM!!!!

I took it to two different gunsmiths back then (one at the old Emroe's in Indy), and both "worked" on it and "fixed" it... and it still does the same thing. It now rests in a locked metal cabinet gunsafe at my dad's with a wire-tie tag on it that reads "gun unsafe - do not try to load or it will fire on it's own"...

I won't take any gun into the field that I'm not 100% sure is right, as it's just not worth the risk of injuring/killing someone around you or yourself...

Call Remington and ask for a new firearm...