Metal Prep for Hot Bluing

[Vernonia MW]

I often struggle to explain how surface prep impacts the finished product when hot bluing guns. This most recent batch of bluing, I had a wide variety of different finishes, and figured it would be a good opportunity to showcase how they impact the finished product.

The AK receiver had zero prep work done. It was left with the mill finish, straight off the stamping dies. I believe this would be similar to how some Chinese AKs were blued. You can see a lot of the details in how the receiver was manufactured, such as tooling marks and spot welds. Any shine that was in the metal prior to bluing is still there, but there is inherent unevenness to the level of gloss.

The G3/Cetme receiver was bead blasted with 80gr glass bead media. It comes out a nice, even matte finish. In terms of effort involved, this is one step above doing nothing. The parts are loaded in the cabinet and then blasted, removing any existing finish and giving the metal an eggshell like sheen. Tooling marks are far less visible or gone entirely. Any pitting that was present from rust is still there, but much less noticeable. It can sometimes appear close to a parkerized finish, depending on several factors.

The Mauser floorplate was polished to 320gr with sandpaper. This is where labor starts to become a significant factor. Sometimes the part gets media blasted first to remove any rust or paint. The part is then sanded with ascending grits of sandpaper. Pitting becomes more visible at this point, and if it is not filed out prior to sanding, can be an eyesore. Some parts were not manufactured with the intentions of being polished (IE Mauser receivers) and have significant tooling marks that take time to smooth over. A brushed finish will hide some sins, but not many.

The Winchester receiver was buffed to a high gloss. Same as the Mauser floorplate, but you continue up the grits up to 1000 or higher, and then move to the buffing wheel and polishing compounds. This takes lots of time, but the results are very attractive. At this level of gloss, any imperfections in the metal become very apparent. Holes that have been plugged and welded will have a different shade of black. Pitting is obvious. Scratches from the sanding process can be visible if done poorly. Just to do the receiver shown was around 2-3 hours of sanding and polishing.

Each finish has its application. I would not want to polish that G3/Cetme receiver. Likewise, the owner of the Winchester receiver wanted it refinished because the prior gunsmith had sandblasted it prior to bluing, while the rest of the gun had been polished. I am a believer that the sandblasted finish can retain oil a little better, and as a result, will not rust as easily as a polished finish. That could be argued, I suppose. I hope this helps someone.

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[Zoolander]

That was a good read, thanks for posting.

 

[Vernonia MW]

Something else to note. My bluing salts were pretty close to depleted. The parts shown were all processed similarly through the hot bluing tanks. The Winchester receiver took on a much darker black. The G3/Cetme receiver was a lighter shade, more of a dark gray. Pretty close to a darker parkerizing. The shade was slightly darker on the cocking tube than the receiver portion, but the cocking tube was surplus (CETME), and the receiver was made by PTR.

The AK receiver was more of a blue-gray. It's going on a North Korean AK build, and will be distressed by the builder, so the color was not critical. Normally I would have redone this one.

The floorplate came out a slightly lighter shade of gray than the Winchester receiver. I attribute some of this to the depleted salts, but likely it has mostly to do with the metallurgy of the steel. It took me two attempts to get it this shade. Many other parts in the bath (that had the same prep work done as the floorplate) took on a darker shade without any trouble. I am still relatively new to the process of bluing, and there is a lot to learn, with few good resources on the subject matter. That's mostly why I am making these posts. Hopefully it saves someone some time.

I also had multiple failed attempts at bluing a Winchester "Nickel Steel" barrel. I had to do some digging into this. Everyone says something different about bluing these. For now, I will be rust bluing it. The next time this comes up, I have some tricks I would like to try. I have successfully hot blued other early Winchester barrels, so I am not sure why this one didn't take. Possibly the depleted salts.

 

[bluebird800]

What is your recommended prep for Rust bluing ?? Ive done several different methods, blast and sand, just blast, just sand. Comes out about the same it seems to me. I dont have a Hot blue set up, but I recently Rust blued an A5 shotgun receiver and barrel. Turned out really great but not quite as shiny as Id hoped

 

[Vernonia MW]

What is your recommended prep for Rust bluing ?? Ive done several different methods, blast and sand, just blast, just sand. Comes out about the same it seems to me. I dont have a Hot blue set up, but I recently Rust blued an A5 shotgun receiver and barrel. Turned out really great but not quite as shiny as Id hoped

I am not an expert on rust bluing. I polish to 320gr and use Mark Lee's Express Blue. It gives a higher shine than media blasting. What rusting solution do you use?

 

[bluebird800]

Ive only used Mark Lee's Express Blue. The color is really great and seems to be quite durable. The last receiver I did i only polished to 220 so likely the reason for the duller finish. Thanks !