Clean it up and "re-silver braze" it. You can see from the photo the original braze was not done well and the coverage was not complete.

This is a good point to inform the novice that the thinner the joint the stronger with brazing and soldering. For silver brazing a clearing of 2-3 thousands of an inch between the lump and the barrels prior to brazing is the goal.

In this particular barrel, notice that there is a pin that aligns/holds the lump in position, much attention needs to be focused upon this detail of alignment before brazing. The craftsman repairing this lump is advised to use a machinist scraper to clean the surfaces of all old braze.

A silver braze with a flow temp of about 1275 degrees F works well for this work.