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Have a chance to to buy a mint browning over and under made in Belgium ,maybe one box threw it . For around 900.. Just wondering what the cost is in opening the barrel to a modified choke, and who could do that in Edmonton .

If you do find someone ask how what type of reamer they use. Many use a standard expandable reamer and these are not piloted. This can be a problem as it has the potential to shift the pattern

tough call
 

If it is a superposed as I suspect in truly mint condition (1 box fired and in the box it is a small group of avid collectors in both Canada but mostly in USA) Seen them go as high as $2000.
When I was behind gun counter at WSS Bob would not even take the used ones in on trade since we had 3 we could not sell. Based on condition he was asking $599, $699 and $799.for over 3 years. Sounds like yours maybe at the top of that price pile. However the market is poor because of the fixed and full chokes.
They can be reamed out by a competent gunsmith owning a lathe and the last fixed full I paid to have done was a 10 gauge Ithaca mag 10 that cost me $75. 2 barrels could be $150 or more.
As has already been mentioned butchering the reaming out can destroy the barrel if off centre. anything I have opened up I have gone to IC since my experimenting shows steel patterns better than in modified.
Another consideration is if this truly is a collectable superpose any modification from a collectors point of view destroys the collectable value.