LAST EDITED ON May-12-14 AT 06:09PM (MST)[p]Your lack of knownledge concerning the correct name of parts makes it very hard to figure out what you are describing.
I may be wrong, but it sounds like your bolt was not pulling the fired case out of the chamber after firing the round and this is what caused you to go to a gunsmith in the first place.
Now you say said gunsmith installed a flat pieace of metal at the end of the bolt and now you can not get the bolt to fully close.
I will take a big guess and figure that you are talking about the forward end of the bolt that engages the barrel chamber end when closed. That rifle used a half circle extractor that set inside the recessed area of the bolt face. Same as for the Remington 700 rifle. In my opinion it is the weak point of remington 721 & 700 rifles as it fails too many times to extract the fired case by slipping over the rim edge.
Some of the old gunsmiths would do away with that remington extractor and throw it out the door. They would machine a slot into the bolt and install a "Sako" style extractor that was far more reliable. If it was my gun, I would go that route and that rifle should be able to give good service for another 30 years or until you shot the barrel out.
You did not say if the bolt would not close when there is a cartidge being chambered, or if it will not close even when there is no cartidge present. If it will not close when trying to feed a cartidge into the chamber, the gunsmith may have installed the wrong Remington extractor. I seem to remember that there was a extractor for magnum calibers and another for standard calibers. It has been over 20 years since I worked on a 721 for extractor problems and my short memory seems to recall there was two different sized extractors that could be used.
Keep searching for a good gunsmith that has worked alot on Remington 700's and send the rifle to him for repair. Just because they call themself a "gunsmith" does not mean they are the right person to work on a paticular rifle brand or problem.
RELH
P.S. I just slapped the side of my head and jogged my memory. Remington made three different extractors for the 721 &700 rifles. One for small calibers, one for standard sized calibers, and one for magnum calibers. Your smith my have put in a magnum extractor in a standard caliber 721 and it MAY BE interferring with the cartidge rim while trying to feed the cartidge into the chamber. Hard to tell from your description of things or lack of description as to what is really going on.