I'm new to this, but from my readings there are as many variations in blueing as there are ways to cook a steak. Then add to this the metal preparation, the degreasing, rusting solution used, humidity, temperature, time, carding method, etc...etc..., all contribute to different results.
That said... I used a 2" PVC with a cap on the end. Suspended the barrel inside and dumped in the boiling water. Produced a nice blue/black. Worked for me.