We have a friend in full-scale firearms manufacturing who was looking at making a large run of 1911 pistols. In order to reduce his machining costs, he bought a sample batch of frame and slide castings from Coast Metal Casting – and they turned out to be next to worthless. So we borrowed a set from him to take a look at. What makes a casting good or bad, anyway? Well, let’s see:
If you are interested in seeing how 1911s were mass-produced before the advent of CNC machines, you’re in luck! We have a copy of an article from Machinery magazine printed in 1942, which discusses the process in some depth:
Making a World-Famous Automatic Pistol, by E.P. Herrick, Colt Production Engineer (Machinerymagazine, December 1942)
Can you say what these frames were too be used for? Possibly a 22LR version? I wouldn’t think castings would be strong enough for any higher caliber, especial since the newly accepted 1911s for the Marines are having cracking problems and those are presumably forged.
They were for standard .45ACP guns. Castings are fine for that, as long as they are made well. Ruger, for instance, casts all their 1911 frames and slides.
The casting techniques and the metals used for gun parts are far advanced from what would be used, say for a cast iron stove.
In the “investment casting” method (aka “lost wax” lost plastic etc) the plastic / wax dummy is moulded to within a few thou of the required size and with due allowences for the metal contracting as it cools, and for a slight excess of metal to be left on critical surfaces which will be machined. The mould which is formed around it retains a very good surface finish, when the wax is burned out.
“Cores” can also be included to give hollow castings. Cores may be amazingly fine and complex, for example the air cooling passages in gas turbine blades.
If needed, the mould can be filled with metal under vacuum conditions and spun to centrifuge the molten metal into the moulds without any gas bubbles or voids.
Depending on the required final use, the metal alloy may even be vacuum melted to eliminate gas bubbles and inclusions.
Once the metal is in the moulds, all sorts of additional techniques can be brought into action; the crystal structure can be seeded (first stage gas turbine blades and bladed discs can be grown as a single, specifically orientated crystal – as creep occurred at crystal boundaries, having the part as a single crystal avoids having boundaries and minimises creep) and can be grown in specific directions.
high pressure gas can also be used to squeeze the still hot casting to collapse any voids or gas bubbles – replicating the effects of forging in collapsing internal voids.
Although it helps to have a part designed from the start with the manufacturing process in mind – as say Ruger and CZ do with their own designs, and as John Moses Browning clearly couldn’t, as the modern process hadn’t been invented when he was alive – parts on the 1911 are not particularly highly stressed and were not designed to use particularly high performance alloys. Just plain old medium carbon steels.
If there are any issues expected with thin sections or high stresses, it is relatively easy to specify a slightly higher performance alloy to compensate – at least with a good casting, you are not throwing 3/4 of the alloy into the scrap skip as cuttings, as you would when machining a forging or from bar
Apparently bent castings are quite common, and Stuart Ottesson (“the bolt action” and “bench rest actions and triggers”) describes some being straightened with a sledge hammer and a simple die.
The micro structure of a steel and the orientation which that micro structure is loaded in a part is very important.
Probably the most understandable reference to start with is this: http://www.amazon.co.uk/New-Science-Strong-Materials-Through/dp/0140135979 , and it’s sequel; structures.
Although hot forging and rolling of metals, collapses and welds up internal gas bubbles, it also stretches out any inclusions of slags, oxides and sulphides.
If these are loaded in tension or shear, the tip of the inclusion or flaw, acts as a stress concentrator, and can initiate a crack. the tip of the crack then concentrates stress and the crack can propagate.
There are several ways around this.
Grey cast irons ordinarily contain pointy ended flakes of graphite; by suitable chemical control
adding sodium silicide to the melt e.g in the proprietry “meehanite” grades results in precipetation of a greater number of shorter stubbier flakes. Addition of magnesium or cerium to the melt, forces the flakes to assume spherical shape),
in both of these the shape of the graphite flakes causes less stress concentration, and the resulting metal is much tougher than comparable cast iron with long graphite flakes.
With materials like hot rolled or hot forged metals, the art lies in expecting the presence of stress concentrating inclusions, and of orientating them so that they are not placed in tension or shear.
A good example of such orientation is the old twisted steel barrels.
The wrought iron and carburised wrought iron steel they were formed from, inevitably contained inclusions of glassy slag, and the numerous welds from the repeated forging, potentially contained voids and oxide inclusions.
By twisting the strips to form a barrel, those potential flaws received only the longitudinal stresses which are only one third of the hoop stresses during firing.
Although investment castings can be produced with an aligned grain structure, there may also be the freedom to add more metal to a particular section, so that a random grain structure can be used, and is less highly stressed.
Back in the late 1970s or early 1980s when Ruger were working on a version of the M14, published photographs showed the locking lugs extending much further allong the lenght of the bolt than in military M14.
The two likely explanations for that are:
to allow for random grain structure
and / or
to allow the use of a cheaper alloy
then there is the ever present threat of ambulance chasers suing, after Bubba blew his face off with a dodgy hand load.
For the amount of work required to use these frames they could start from scratch.
I had the same problems when the company i worked for, took the decition to make a series of an equipment.
We used the methods of lost wax and lost plastic.
Allthough the accuracy of the procecion of lost plastic is about 0,1mm, neither of them is suitable for delicated casting…
We had the same problems – and many more… It is the shape of the cast part that gives all the problems.
A lot of maney spent to go back to basics…
After that the parts from aluminium casted with the method of wet sand and the others with lost wax… That is why i do not think that the gun production companies use cast parts to their products…
Both Cz and Ruger use investment casting for many parts of their guns, and have done since at least the 1960s (I think Cz/Brno, was the pioneer).
However those guns were designed to use investment castings, and critical surfaces have additional metal cast into them to allow for machining.
There are some interesting fudges built into some of those guns, for example, Ruger M77 bolt action rifles, have the bolt way and associated lug race ways cast in.
The machining of the locking seats and the threads for the barrel are not referenced to the bolt way.
To allow for the expected eccentricity between the bolt way and the axis of the barrel, the bolt face counterbore is given an extra large clearence, so it does not bind on the sides of the case head.
Because of the casting process allowing complex shapes to be formed cheaply, both Ruger and CZ were pioneers of casting scope mount dovetails into the receivers of their guns.
[…] E.P. Herrick, and published in Machinery magazine for December 1942 His full post is here Looking at 1911 Castings | GunLab The link to the .pdf is at the bottom of the post. It's a pleasure to find first hand […]
I am wondering how qualified your friend is to manufacture 1911’s if he doesn’t understand that regardless of the casting, it will still need to be surface ground (look at a Caspian, Baer or Ruger 1911) which are among the 1911’s that start life as a casting. All of theirs are surfaces ground on the finished product.
Also, any slight bend in the frame is from the heat treating process. That is why there is extra material to be surface ground.
Then you placed the frame on it’s top to show the gap in the top. That is where the gate is and it is intended to be machined flat.
If your friend is expecting a casting that will require ZERO surface grinding or machining of the gate area, he will be sorely disappointed. If he found a source that sells castings with such qualities, i am sure everyone in the 1911 community is interested.
^^^^ Winner , the guy bought an 80% lower and upper and he was expecting it to become a ready to go piece almost out of the gate ???
Fair warning for $30 castings? Are these concerns less of an issue for the one off DIY’r verses production runs where time equals money.
This is not really a complete story. From an arm chair quaterback’s perspective, the missing detail is what tolerance spec did the casting contract require and at what price? I find it difficult to grasp why a guy proceeded to blindly build a run of pistols without submitting drawings, expect proven samples and acceptable limits for quality castings from a reputable source. Can’t imagine any arms manufacturer buying them before verifying they met his minimum requirements.
In many castings there are secondary processes to tweak the parts into tolerance prior to machining anything.I have machined enough castings to know not all have pads and very rarely are they net where it matters. Where they do lack tooling points, your tooling can make up for that to at least get the first few machined surfaces to reference everything else from within the cast envelope. All other surfaces would be cosmetic/structural, but still your prides stamp of approval to fit and finish.
The parts that hold the bang inside are a whole lot more critical. It would have been interesting to see what a CMM point cloud would show as to where the skin of that casting is compared to a solid model to reveal just how close to worthless junk it was.
Has anyone come up with an easy to do at home way of casting a magazine well into a home cast aluminum frame yet? Yes, I know the trick of using a dummy silicone sand magazine to preserve the void, but I find postitioning it in the lost wax model to be a total pain. Is there a better way to leave the void in when home casting a frame>