Melonite. First, what is it?
That word is just a proprietary term for Salt Bath Nitride. Something that has been around for years. In the gun world this really took off around 10 or so years ago when guys started having barrels "cooked" so that they'd last longer. Mixed results were the general consensus. The big reason is, you have to be very careful in how you do it. "SBN" effectively brings the shell hardness level of a barrel into the 50-60 Rockwell range. That's great for a bore as it'll just wear longer. The issue however can be the throat. You would want to run a couple hundred rounds down the bore before sending it off. Failure to do so can result in a barrel that just takes a very long time to settle down.
So, that covers the ghist of that stuff.
Onto receivers:
People want this in the hopes it'll make a bolt run smoother. I get that. However, you really, really, need to take a long and hard look at what you are doing to the basic chemistry of the steel. It matters.
For instance: An action made from 416R stainless will typically heat treat to around 42-44 Rockwell C scale. This is done around 1500-1600 Degrees. It's an air quench material. So, you get it hot, soak it at that temp for awhile, then quench it by blowing an inert gas, like nitrogen over it, so that you don't suffer any oxidation ( or hydrogen embrittlement ). Then your done. A lot of aftermarket action companies like this stuff because you can machine it easily after heat treat and it doesn't tend to move around and distort a whole lot. Great for the bottom line because tooling costs and machine requirements don't go through the roof, and you can finish the parts and be done with them. Easy and that keeps costs in at a level folks can live with.
If done right, conventional heat treatment will get the hardness to penetrate all the way through the material. Very good as hardness directly correlates to ultimate tensile strength, toughness, etc. All things an action requires.
Now, go cook it in some ammonia based salt at around 900-1000 degrees Fahrenheit. The surface hardness will increase to around 50 or 60 rockwell C scale. This is great, but...(always a but) WHAT did it do to the core's hardness and tensile strength? 416R anneals at around 1100 degrees. Annealing removes hardness. Your within 100 degrees of that temperature. Don't fool yourself into thinking it wont influence the final outcome. Steel is not an "on/off" switch. The chemistry of the material fluctuates just like it does in a loaf of bread, so how it behaves changes as well.
Using 416R SS as the example, its chemistry is rather complex when compared to something like chromoly. The way you approach these two is quite a bit different and that really needs to be respected.
With 416R, you essentially make a hard boiled egg. Hard shell, with material that runs the risk of being softer inside and losing tensile strength.
My point here NOT to say this happens with all actions, but make no mistake, it does happen with some and its solely based on the material that the receiver is made from. You really, really want to know the exact steel composition. Failure to do so might get you an action that essentially becomes a time bomb with a very unpredictable timer...
You sneeze a case by over pressuring it or having some sort of just worst case scenario event, you may just go on with your life, or you could very well end up picking gun parts out of your face.
Having done that once, I don't recommend it.
Know exactly what you are asking for and make sure the folks doing it know as well. ASSUME NOTHING.
Last edited by C_Dixon; 11/28/18.
