I have a .177 mk 5 Airsporter (in amongst a collection of Airsporters and Mercury's) which has some pretty bad corrosion in the rifling, and was thinking about putting it in the lathe and cutting off and boring out the old barrel, and having a go at fitting another. My problem will be the fitting of the barrel up to the loading tap area and ensuring good alignment and seal and fit for the tap. Anyone got any thoughts or experience doing this?

My initial idea is to use an end mill to bore the old barrel out in the action, just short of the loading tap, and then align the new barrel bore to the action hole in front of the tap, before brazing.Hope this makes sense.

It is a spare action and not a complete gun so I dont have much to lose, and I am an engineer by trade so I dont find anything like this daunting, just interested to see if anyone has done anything similar or got any ideas. I know a few on here build the older BSA under-levers from parts, and heavily modify, so thought I would enquire.