The bluing properties would depend on a careful match of base metal (barrel, action, etc.) and filler rod. Hard spots would depend on how the base metal alloy reacted to the heat of the welding. Since pits are generally small (both size and volume), the amount of heat and hot metal is small relative to the size, shape, and volume of the base piece. So, this work can be generally done without warpage. The "smallness" of what can be done is pretty amazing. BTW, I predict a pretty good market for the first guys that do good barrel bore pit filling.
