There have been a lot of people doing upgrades .I have seen a lot ,some are excelent and have been done to a very high standard .Others have been done to a budget and I've had the misfortune to have one or two of these in for corrective work . One had bad barrels and was only .001" in proof another had had a 1968 Birminghan reproof at.740"!!!Not to mention odd extractors and butcherd inside work .
I saw some done by John Foster, for example, that were built on top class actions with all bore and choke sizes as original .When it comes down to the bottom line you get what you pay for,but be certain what you are paying for.
Have a look at the photos.
www.johnfostergunmaker.co.uk
