Pouring Brass Barrels

[mark brier]

In response to brass pistol barrel in the black powder shooting forum I have been asked to post some pictures of the process. I have some pictures from pouring  2 barrels this past weekend. This is to make a matching pair of pistols which will be 100% hand made. Having poured all the brass for rifle or pistol hardware for most projects I figured why not pour the barrels, can't be any harder than forging my wrought iron barrels. First I made a wood pattern out of some poplar by gluing 2 blocks together with paper in between to allow separation later. I then profiled the barrel for a 10" swamped barrel and installed indexing pins and turned 3/8" round sections on each end to make the shelf inside the mold to lay the core into. I also drilled the 2 holes in the match board to hold the bottom half of the pattern when ramming up the drag side of the mold. The pattern comes out with the match board, then just put the pattern back together and put back into the drag and ram up the cope half of the mold. I did not get pictures of the next few sections because I didn't know I would be posting and already had the crucible in the forge with naval brass melting so I had to hurry up. Separate the mold and remove the pattern and I cut the casting gate into the drag section to go into the funnel shaped pouring cup of the mold. I also cut a vent on the other side and also pushed 1/16" tig rod thru the barrel section of the cope to vent also. Laying the 3/8" core into the drag section I then put the cope back onto the drag and clamped the top and bottom of the flask together because I poured the barrels vertically and remove the ends on the top of the flasks. The  picture shows the barrel as it came out of the mold with the casting sprue cut off. Followed by the barrel roughly filed just to clean it up and inspect. Also you can see the 3/8" bore waiting to be bored out to whatever caliber. Pictures will follow shortly.

Mark Brier

[jerrywh]

 This will make the 12L14 discussion look mild. 

[gizamo]

How do you pour high tensile strength brass? Interested in your process...
Are you lining the barrels?

[Joe S.]

This will make the 12L14 discussion look mild.

you think?should be very interesting

[Eric Kettenburg]

What did you use for the core?  The first one I did, I used a steel rod and sooted it up (i.e. with lamp black) very heavily, but had problems with portions sticking.  And I mean, I really sooted that sucker up.  After that I read somewhere about using a rod coated in clay, and tried that, which worked perfectly.  Once cool, stick the casting in a vise and just give the protruding end of the rod a whack with a hammer.  Boom, worked perfectly, rod shoots out the other end and clay shatters to almost dust.  A few years later, talking to Brad Emig who used to be right next to me at Dixon's, he mentioned exactly the same process.  So, curious to know how it is that you prevent the core from sticking and if one of these methods.

I promise I won't bring up the liability aspects as per the 12L16 thread hahahahahahahaha.........

[mark brier]

Gizmo, I poured it the same as any yellow brass as far as temperature goes. I would gauge the temperature by inserting a steel rod into the crucible long enough for it to reach the same temperature as the brass and then withdrew to check the color. I also would look visually to see if the brass was boiling and also would place the tongs on the crucible to feel if the brass was churning or boiling.

Eric, as far as the core I first experimented with sand and waterglass, but was not happy with the results. I was going to use a 1/4" wrought iron rod with clay as you talked about but thought lets try keeping it simple. I took a section of a 3/8" hickory ramrod blank and charred the outside of it with a propane torch. Worked great for

Mark Brier

[mark brier]

Gizmo, I have no intention of lining the barrels....... See how they proof

[JCKelly]

Druther use this poured brass barrel than one of 12L14, thankee very much

Minor question - exactly what brass, by chemistry, are you using?

Brass, roughly 70% copper 30% zinc that is, does not shatter as does steel when it is cold.
Brittle behavior is a peculiarity of steel.
"Cold" for hot rolled steel bar or angle tends to be around the freezing point of water.
"Cold" for 12L14 is about 70F (21C).

Porosity could be a problem with any copper alloy casting. Beyond knowing this, I am not a foundry expert.

[Eric Kettenburg]

Anything I've poured has been pretty much straight cartridge brass, i.e 70/30 with maybe some added lead.

Castings that are poured too cool can be porous, and likewise, also if too hot as if the brass is boiling excessively there will be too much 'bubbling' - my non technical description.  Porosity can also be a result of green sand that retains too much moisture or oil based sand like Petro bond (which is what I went over to using as it's much less temperamental in non climate controlled buildings) which has too much oil in the sand, or used sand mixed with unused sand in a poor mixture ratio.

[davec2]

In casting cannon, the original process was to cast with a core and then clean up the bore.  However, that puts the worst of any shrinkage porosity (i.e. worst material properties) between the core and the outside dimension of the casting.  In casting cannon (brass or iron) that led to so many failures that the standard process came to be casting the barrel solid and then drilling out the bore.  That way the weakest part of the cast material was now down the centerline of the casting and would be drilled out in making the bore.  This was, of course, no easy task when one is talking about drilling a 4 or 5 or 6 inch diameter hole several feet down a casting that often weighed from a few to several tons.  (A finished 24 pounder, for example, weighed as much as 6,000 pounds).  For something as small as a pistol barrel, I would think that casting it solid and drilling out the bore would almost be easier than casting around a core with the added advantage of removing the most suspect part of any casting.

Cool casting though.

[Bill Raby]

   I spent over 20 years casting non-ferrous metals almost daily. Mostly gold, silver, platinum, palladium. But copper alloys work about the same. And mostly lost wax under vacuum or in centrifuge with controlled temperatures. Never did any sand casting.

   The problem that you have on something like this is pitting. Visible holes are obviously bad. That is caused by air bubbles that did not escape before metal solidified. Not a big concern though. Open them up with a ball bur and weld in a plug. What is going to get you in trouble is the microscopic pitting. Metal crystallizes as it goes form molten to solid. That makes it shrink in addition to what you get from just the change in temperature. Think of as a firewood dumped in a pile compared to carefully stacked firewood. It takes up less space. On a swamped barrel what happens is the thinnest part cools first. The middle. The ends cool last. As the part at the end of the mold cools, it crystallizes and shrinks. It tries to suck in more metal to fill the space. What sometimes happens is that the metal will pull away from the side of the mold. Usually the weight of the metal above is enough to prevent that from happening. So it pulls in the metal above. In a swamped barrel that will be from the middle of the barrel that is already cooled. At that point it will be in a plastic state. Still semi fluid. That stretching is where you get the microscopic porosity.

   At the other end, at the top of the mold, the same thing happens. The difference is that you have that large cone of metal where it was poured in. It is going to draw metal from that. But it is larger and cools slower so it is still liquid and can flow in easily. Am I making any sense? The metal cools from thick to thin. You don't want any thin spots between thick spots. On a swamped barrel the problems are going to come up in thinnest part of the barrel. The solution is cast a reservoir that feeds into the bottom of the mold and can be cut off later. Or you can vent the mold there to cool it faster.

   You always want to cast non-ferrous metals as cool as possible. It turns into a bit of black magic here. Need metal liquid enough to fill in the mold and no more. Gun barrel is rather easy. A large piece of filligree needs a lot more heat. The mold needs to be as cool as possible also. If mold is too cold the metal flash freezes on contact and does not fill in. Anyone casting lead balls knows this. A mold too cold does not fill. A mold too hot leaves a frosted surface. That frosted surface is microscopic porosity. Metal temperature can make a big difference also. Boiling obviously makes a bad casting. But at high temperatures alloys can start to separate. Oxidation is also a concern. Especially if you are melting the metal with a torch. Need to use boric acid or something similar to prevent that.

   How the metal was melted can make a difference also. Most likely you used a oxy/acetylene torch. That is what most people have. Puts out a lot of heat. But has a lot of carbon. At high temperatures carbon does stuff that it normally does not do. With brass I doubt you got it over 2000 degrees. So not much problem. Some of the platinum group alloys cast over 4000 degrees. Carbon destroys the metal at those temps and you are limited to either hydrogen torches or induction melting. I got to work with osmium once. Melts at about 5500 degrees. What a nightmare! Need goggles with gold plated lenses and get severe sunburn. All sorts of weird chemical reactions going on at those temperatures.

   But back to brass pistol barrel. It looks fine in the photos. What will cause problems is microscopic porosity caused by casting with variations in the thickness. Don't have too much variation in there so it might be just fine. But there is a good chance that you have porosity. There can be sections that are mostly empty space. Sort of like a sponge. Looks like you got it filed. What you need to do is polish it to a mirror finish. If you can get a mirror finish on the whole thing, the barrel is good. But if you get any spots that will not take a mirror finish and have a sort of frosted look, you have porosity in the barrel and it is not good.

[JCKelly]

Wow

[Joe S.]

Hmmmm,lots of good imput there.Almost sounds like you would want cast this thing without the swamp and work it in later to help reduce the risk of porosity. Kinda taking me back to my metal shop days in highschool.I remember doing sand-cast pours of flat objects in aluminum. Of course it's apples and oranges seeings how it was not a gun barrel but remembering the shop teacher saying some of the same info.Very interesting threads lately on gun barrels,interesting indeed.

[SingleMalt]

I'm quite impressed.

[mark brier]

Melting was done in a coal forge and I put in a little more borax just before the pour to clean once the metal once more and to use it as a degasser

Mark Brier

[somehippy]

It's stuff like this that makes this site the best one around.  Unending learning! I just can't believe so many handy people gather in one place lol. 

[Bill Raby]

Hmmmm,lots of good imput there.Almost sounds like you would want cast this thing without the swamp and work it in later to help reduce the risk of porosity. Kinda taking me back to my metal shop days in highschool.I remember doing sand-cast pours of flat objects in aluminum. Of course it's apples and oranges seeings how it was not a gun barrel but remembering the shop teacher saying some of the same info.Very interesting threads lately on gun barrels,interesting indeed.

   I would not worry about casting a swamped barrel. It gets thinner in the middle, but not by very much. I doubt that it would be a problem. Especially with a fairly thick barrel. I was doing custom jewelry work and customers would come in with all sorts of wacky ideas that would be next to impossible to cast. Ideal situation is to carve the barrel from carving wax then make a silicon mold of it. If the casting does not turn out, just use the mold to make a new wax model and try again. Casting with the mold under vacuum or in a centrifuge makes it work a whole lot better. You can run everything at lower temperatures that way. But of course this all requires thousands of dollars of equipment and all historical accuracy of the method goes out the window.

   It really is important to polish a cast brass barrel to a mirror finish. If you can get that over the whole thing, the casting is good. You can always take some steel wool to it if polish is not desired for the finished piece. A frosted surface that will not polish out is porosity. It does not look like much, but under microscope it will look like a sponge. It is mostly empty space. It will be brittle and very weak. Good news is that the porosity tends to mostly appear just on the surface. You can often file it off. But if you take it down more than about a half millimeter or so and still have it, it likely goes all the way through. Melt it down and start over. A barrel with porosity is almost certain to burst. Copper alloys tend to cast with porosity even when you do everything right.

   I have lots of experience with casting, but I would not cast a brass barrel. It is certainly possible to cast a good barrel, but machining one from billet would be a lot less trouble.

[Goo]

I have a friend in his late 70's now who's father did casting for the auto indudustry. Their facility was located in Detroit at that time and described to me that this company produced porosity free castings.   He described the process to me this way.  Polished wood patterns were set into metal mold frames, the frames were half with machined mating surfaces.   The patterns were set into investment which were fired in a kiln then by some great amount of skill the mold frames were mated metal poured and air pressure was applied before the pour could solidify producing a non porous casting.   I have seen and held items made by this process and they ring when tapped.   My friend has offered to work with me to show me the process first hand and as I learn more will post updates over time. It seems to me that bronze or brass barrels would be doable this way alleviating much of risk factor.

[Bill Raby]

   Air pressure certainly helps. Actually they usually use nitrogen and induction heating to cut back on oxidation. When they do this they also vacuum the air out of the bottom of the mold as the metal goes in the top. That way you can cast with under cuts. This in itself does nothing to reduce porosity, but it does allow to cast with a lower mold temperature which makes a huge difference. Think of casting balls or bullets. If the mold is too cool metal hardens before it fills in. If it is too hot, you get a frosted surface. That is porosity. No big deal on a lead ball. With an ideal ball casting the metal will shrink as it cools and crystallizes. As it shrinks it will draw in more molten metal from the pool of metal on the top of the mold where you poured it in. Bullet and ball molds never have a large enough reservoir to keep it molten until the ball hardens and it is exposed to cool air. So when the ball tries to draw in more metal, there is nowhere to get it from. Then you have porosity. The hot mold tends to put it on the surface of the ball. With a cooler mold the porosity goes in the center. But when you use the right size reservoir you have a supply of liquid metal to feed it as it cools. No porosity. At least in theory.

   If you were to cast a flat sheet of metal instead of a ball, you would need a higher mold temperature. You do not have such a large mass of hot metal inside the piece so the surface tends to flash freeze when it touches the mold and it does not fill. You have to adjust mold temperature for the shape of each piece that you cast. It gets tricky when you cast a piece with both thick and thin parts. You need to use multiple sprues of different size, add internal metal reservoirs, and with pressure over vacuum, you can use the air to cool specific parts inside the mold.  There is no real science to it and it can take a lot of work to figure it out. I can show you how to cast in an afternoon, but it takes a good ten years to really know what you are doing. That is why most cast pieces that you are designed to have a fairly uniform thickness. Pressure over vacuum fills the mold much faster and breaks the surface tension to fill small details. On a brass pistol barrel cast this way you could probably drop mold temperature down to about 600 degrees.

   Change the metal, or even the alloy, end everything else changes. For platinum I would cast 4000 degree metal into a room temperature mold. Need a centrifuge for that. Scary. Why? It hits the mold with enormous amount of force. If the mold cracks it sprays out all over the room. I still have about $1000 of platinum in my leg. Looks like a bullet on a x-ray.

   The neat thing with buying rough cast gun parts is that they still have the sprues attached. Notice where they put the sprues on buttplates and how trigger guards almost always have multiple sprues. Trigger guards have those metal tabs on them that you drill through to pin it to the stock. Those are the sprues. They seem to often be in the wrong places. A lot of times there are extras that you have to cut off and file down. And they are always too big. Buttplate sprues are often on the most curved part making it extra hard to finish. Its not because the guy that made it knows nothing about building guns or is just trying to make your life more difficult. That is just how you have to do it to make the casting work.

   If you get a spot that will not polish on a brass piece, the easiest way to fix it is to just pound it with a hammer. Porosity is just a bunch of little air pockets. Hammer can mash them down. It will make the metal any stronger. But you can likely get it to take a polish.

   Don't cast a brass barrel. Make it out of a drawn rod with a milling machine and lathe. Too much can go wrong with casting even if you know what you are doing and have the equipment. And you can get brass rod in whatever hardness you want.