Unless you really want to DIY just talk to DM80. He did my 127 and it came out very well.
You could could blue a barrel I did one on my Ratty but it will never be as good as the hot blue proccess.
To cold blue.
Polish off all the old bluing and any marks on the metal, bluing dose not hide marks.
- De-grease well I used Gunk car engine de-greaser.
Cover the steel with whatever bluing you have chosen to use.
Wait a few moments then wash it off. Rub over very gently with very fine steal wool. Dry the barrel inside and out
Repeat 2 until you get the finish you want.
Better to have it hot blued!!
Ora