Metal type for shotgun magazine tube extension

[737mechanic]

I have a mossberg 590 with 18.5 in barrel and was wanting to give a shot at making my own magazine tube extension and was wondering what type of steel would be best. I was thinking 4140 but not sure if that would be the way to go. Any thoughts would be helpful.

[Harold_V]

If the extension does nothing more than house shells, there's no need for chrome moly, although there's certainly nothing wrong with making that choice. That may not be true if any welding is required, for anything higher in carbon than 4130 could prove troublesome (that includes 4140, which can be welded, but requires heat treat immediately afterwards).

Before you jump in with both feet, know that some alloys, when heat treated, don't blue, but turn a dark copper orange color instead. I don't expect that would be an issue, but it doesn't hurt to investigate the possibility if you'd be unhappy with the color.

Harold

[737mechanic]

Thanks Harold, I will need to have it parkerized when it is done and would like to get close the the factory mossberg tint so if I could find out what they use would be great. My main concern is I was wanting to machine this from a solid bar which will require me to bore a .900 hole about 4 in deep so a steel with good machining would be a big plus. If that does not work I can also start with some think wall DOM tube and just weld the end up and machine it down. Not sure what the best way to go would be but I was really wanting a fully machined part from solid stock if possible.

I can get 12L14 bar would that be too weak for something like this you think.


Here is a picture of what I would like to make or get close to at least but without the sling attachment.
click here

[Harold_V]

Thanks Harold, I will need to have it parkerized when it is done and would like to get close the the factory mossberg tint so if I could find out what they use would be great.

I am not aware of what may or may not alter the appearance of the finish with Parkerizing, so I'm no help there.

My main concern is I was wanting to machine this from a solid bar which will require me to bore a .900 hole about 4 in deep so a steel with good machining would be a big plus.

In a sense, that rules out chrome moly. It's not known for its ease of machining, and does tend to tear, somewhat like mild steel, albeit not nearly as badly. If you can overcome the toughness and minor tearing, boring a hole that size and deep isn't beyond reason.

That would tend to If that does not work I can also start with some think wall DOM tube and just weld the end up and machine it down. Not sure what the best way to go would be but I was really wanting a fully machined part from solid stock if possible.

If you were intending on bluing, welding would most likely not be a great choice. It would be uncommon for the joint to finish the same way as the balance of the material, but that may not be the case with Parkerizing. I can see, clearly, that I need to learn more about that process (which I quite like!). As far as the material choice is concerned, DOM is cold finished and develops very good machining qualities, much the same as Stressproof. It would be an excellent choice from the standpoint of machining, assuming finishing the weld isn't an issue. That I can not say.

I can get 12L14 bar would that be too weak for something like this you think.

Outstanding choice as far as machinability is concerned, but it may not respond to Parkerizing. Dunno!

Here is a picture of what I would like to make or get close to at least but without the sling attachment.
click here

It always helps to see a picture, so thanks for posting.

Please be advised that pictures that are linked to the forum should not be larger than 800 pixels in width (height isn't an issue). Those that are tend to spread text off the screen for folks with older monitors. As a result, I have edited your post so the picture must be clicked to be viewed. That helps folks with slow connections and old monitors.

It will be interesting to see how your project shakes out. Please post again and let us know.

Harold

[GeorgeGaskill]

I would try Parkerizing a sample of whatever you decide to use for the part before making the part. I am not sure what the lead in 12L14 would do when Parkerized.

[jbmillard]

I have parkerized 12L14 with no problems. I just finished a scope base and used a manganese phosphate solution to parkerize it -- came out nice and black.

[737mechanic]

jbmillard Thats good to hear, I just recieved 2 feet of 12l14 so I will get started on this project soon. I will post the outcome when and if I am succesfull.

[Harold_V]

I just finished a scope base and used a manganese phosphate solution to parkerize it -- came out nice and black.

Can you talk a little about the process? I've always been interested in Parkerizing. Did you buy prepared solutions, or does one put together the required chemicals?

Harold

[737mechanic]

I just finished a scope base and used a manganese phosphate solution to parkerize it -- came out nice and black.

Can you talk a little about the process? I've always been interested in Parkerizing. Did you buy prepared solutions, or does one put together the required chemicals?

Harold

I would be interested in info on the subject of parkerizing also.

[737mechanic]

Well I was in the garage today and decided to get started on the extension and I got alot further than I figured I would. The thing is almost done except for the grooves in the matting face that contacts the tube mount. There is a little spring loaded ball that engages the grooves and keeps it from backing off. I just need to get my rotary table set up to do this. I have a friend at work that has the parkerizing setup and he is going to handle that for me then it will be finished.

It works and functions perfect but the knurling didn't turn out the way I wanted but it does its job so I will see if I can live with it and if not I will make another one.

The one thing I had to do was grind a square threading bit because the threads on the mossberg are a square thread worked out good though.

[Harold_V]

Well done!
If you attempt to make a second part, I'd be ok with talking about starting a good knurl. There's a fail-proof approach that I've used for the bulk of my machining career, and it's dead easy. Doesn't necessarily make sense, but it works, and it works every time. That's what counts.

Harold

[737mechanic]

Thanks Harold, I would be interested in hearing about your knurling technique. Mine is hit and miss and usually when I am really wanting a perfect knurl I get a screwed up knurl and when it doesn't really matter and I just need to get a project done quick I get a perfect knurl.