I’m sure this topic has been covered but I can’t seem to find anything on it. I am in the process of building a Walker Hepburn from a kit. 

I bought a barreled receiver that was smoked and had almost no parts with it. I’ve got a hammer, a regular Hepburn breach block and receiver, everything else is from the kit. I’ve got an aftermarket 32-40 Win barrel that will go on it.

I read up a little about annealing the receiver and people’s opinions, don’t think I’ll need to do that. I plan on nickel plating or rust bluing the parts. Do they need to be heat treated? The lower tang and lever and such I think not, but the breach block takes some abuse.

Logan

Johnny,

I bought the kit second hand, the receiver and hammer are original, everything else I will use from the kit. I’m more wondering whether it is necessary to case harden or heat treat the parts. Can I just go straight to nickel plating/rust bluing?

Logan

If the action and hammer are originals I can't see why they'd need to be heat treated? They already are heat treated for many decades now.

Logan,
You stated in your post. "I bought a barreled receiver that was smoked and had almost no parts with it."
Was the receiver in a fire?
If so, it should be checked for fire damage. If not, I'd agree with Marlinguy.
Rodney Storie told me that his castings used 8620 steel but that some castings in the past used 4140 steel. 
Untreated both steels should be safe with low pressure cartridges. However, the heat treatments are significantly different with these two steels and 4140 can become brittle if not properly heat treated.
I don't know an easy way to tell 4140 from 8620 and never could master the spark test. Maybe one of our members could help?
Otto

If you have cast parts from the kit that still have excess metal on them in the way of a casting sprue or other excess mold flashing , etc...
You can cut those pieces off and try home HT on them.
If they harden after heating it to a bright red and quenching in oil or water, then you have a thru hardening steel such as 4140.
It won't tell you other than it is a thru hardening high carbon steel, the exact alloy like a 4140 would be a guess.
But at least you know it is able to be hardened by HT.
Do not send it in for case hardening as it will end up brittle hard all the way through.

If the sample(s) end up just as soft and easily cut with a file after the heat and quench,,then you have a low carbon steel (like 8620,,but again exact alloy unkn).
These can be safely CCH. The core will remain soft.

Try and take a sample of metal off of one of the 'critical parts' in the kit. One that is expected to be hardened (trigger,sear, etc.
Screws and pins may just be a low carbon steel, but not necessarily.
Cast springs are usually a different high carbon alloy all together