I need your help in locating a finishing chamber reamer.....please read the following sad story:

I acquired a partially sporterized No. 4 Mk1 in 303 british. It had been restocked, barrel shortened and metal brought to 'silver'. I have chamfered the badly cut barrel' satin blued the metal changed out the trigger and scoped it.

My problem is that the previous owner had 'left' a small piece of brass in the chamber that dents the shoulder of any brass I fire. I tried to gently remove it but it appears 'welded' to the chamber. The elegant way to correct this is to take a finishing reamer and gently cut the brass out without changing the chamber dimensions.

I have had no luck finding a gunsmith that can do this work locally. Nor have I been able to locate a reamer that I could rent or better yet borrow for a day......anyone have a lead?
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