Limited to steel and only steel, but a coating that has stood the test of time and damn near every military on Earth! Hard run full-auto or safe queen...both will look the same if maintained properly. Think of park as a surface sponge for protective lubricants. Keeping that in mind, what about using it as a base coat under a ceramic, teflon, or urethane coatings?

What are the benefits?
1) Parkerizing can go where few finishes can as it is one of the thinnest coatings available, nor is it limited by where a spray gun can reach, or operating temperatures.

2) The finished product with a parkerized base coat will gain added impact resistance and makes it harder to scrape down to bare metal from a bad spill.

3) For DuraCoat finishes, we see added adhesion benefits when joined with a Zinc Parkerizing base coat.

What is the down side?
1) Surface thickness will increase which can create wear points in places that did not have the issue previously. An example would be holster contact points. Tight fitting retention holsters will be even tighter fitting. Furthermore, hand fit weapons like custom 1911's that have little or no slop between parts may require some refitting.

2) Park base coats kill sheen. If you are looking for the flattest sheen level you can get, this is good; however, if your after more than a satin sheen, stay away from this option.

3) Surface texture is not as smooth as without this option. Like the difference between a sheet of paper and a sheet of glass to the touch.

To put it simple, if you are going to beat the hell out of your rifle from use, a park base coat is a good idea. If you have a custom Wilson Combat 1911, this is NOT for you! You can use Manganese or Zinc for a base coat. Either will add benefit to your overall finish. Zinc, however, is the smoothest of the two and contains the highest crystallization which provides the best bonding surface with any over coat of choice.