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Well, the metal needed is driven by the chamber pressures.

Shotguns have relatively low pressures - say, oh, 14,000 PSI to 17,000 PSI. Black powder shotguns need even less.

Pistol/revolver rounds might reach up into the mid-30K to 40K region (for the biggest Linebaugh or Freedom Arms type rounds). 25 to 30K for most centerfire pistol rounds is a good number.

Rifle rounds can be anywhere from the mid-40K region up to over 60K PSI, “maximum average pressure,” aka “MAP” to firearms testers and proof houses. Near 70K PSI in a rifle, you start blowing out primers and case heads start to come loose.

OK, so what does this mean?

It means that many steels will actually suffice to hold in those pressures. The steel used in the receivers of the Springfield ‘03, Garand and M14/M1A aren’t what we currently consider especially high-strength steels. If you want a representative AISI number, go look at the specs for 8620, which was the steel of choice for the Garand and M14. The ‘03 was similar strength, different steel.

Barrel steels were “ordnance steel,” which spoke more of the quality than the yield strength. Today, most “chrome moly” steel barrels are 4140 steel, “gun barrel quality,” which is the highest quality of that particular alloy. Basically, you don’t want inclusions and pockets in the steel. Stainless barrels are typically made from 416 stainless - but mostly because 416 machines nicely, not because it is especially corrosion resistant or high strength.

4140 alloy is pretty common stuff. If I had to pick only one steel in a survival situation, I think 4140 would be high on my list of “good stuff to have.” You can harden it, you can work it annealed or quenched & tempered back, you get good machineability, good welding properties... there’s a reason why it is so popular in so many applications.

Springs: Springs are typically made from much higher carbon steel than anything else on a gun. Whereas the barrels are made from 4140 (which is 0.40% carbon), spring stock is typically 0.70 to 0.95% carbon - much higher. Typical spring AISI numbers are 1070 or 1095 - plain carbon steels with high carbon contents. This isn’t complicated steel to come by, but the heat treating of a spring is the issue here. You have to heat it to about 1450+ F, then quench in oil, then re-heat to about 650F to temper it. Putting it into a pot of molten lead works, or a bath of molten saltpeter works well too - and blues the spring at the same time.

None of these are especially “high strength” as modern material science looks at it. To see what I mean, compare the yield strength of 4340 steel to 4140, and you’ll see a modern “high strength” steel.

Pins and screws: Screws are machined out of “screw stock,” which is relatively weak steel that machines really nicely - like 1215 or 12L14. Pins will be harder stuff - the 1070 above would work, altho a tool steel might be a better option.

The point being: None of the steels in a modern firearm need to be what we call “high strength” - they’re good, don’t get me wrong. But that’s all they are: good. They’re not some wonder steel.

And... if push came to shove and you had to go back to black powder, you can make firearms out of malleable iron - not steel. The first gen Colt SAA’s, some of the Winchester rifles, etc were made of malleable iron - which is why color case hardening was so popular back then. It was the only way to keep the malleable iron from denting and scratching...

Looking at the alloys being used by the laser sintering and the print-n-bake printing outfits, it appears that they have the steels necessary for the action/receiver and barrel already in use in 3D metal printing. This doesn’t surprise me, because MIM gun parts are working just fine and are probably made from the same types of powdered steels.

I have no doubt that they’ll be able to make an entire gun on a 3D printer in the near future. It’s coming - as soon as some gun nut with the appropriate background gets near one of these half-megabuck machines for a weekend, it’ll get done.