Minimum chamber thickness

I’ve seen old revolvers with very thin cylinder wall thickness, like these for example https://www.kirstkonverter.com/ruger-old-army/ruger-converters.gif

Back in the days the quality of the steel was inferior, so it got me to wounder about the steels of today.

What’s the minimum thickness of a chamber in cal .40 containing a 25-30 grain FFFG black powder (or equivalent pyrodex P) load with a 92 grain lead roundball tightly infront of it (+wadding) if it’s made of a steel with following properties:

Yield strength min [MPa]
700

Tensile strength [MPa]
900-1050

Elongation A5 [%]
12

Hardness
270-325 HB

And how many PSI will such a load described above generate?

Calculating the pressure a tube will withstand is easy, called "hoop stress".

hoop stress.. - Google Search

Here are examples of black powder pressures.

black powder pressure - Google Search

Bill

This is the best single resource I’ve found, it’s CIPs minimum chamber wall publication for various cartridges, and they are provided for four grades of steel.

The main issue is Europeans typically use better steel than the American manufacturers, 4140 falls at the low end of the steel groups in this analysis. But you can go a heck of a lot thinner than most would anticipate, for instance with the best steels a .308 requires .130” minimum chamber wall.

I’ve used this data in building ultralight rifles and double rifles, where barrels as slim as .100” at the muzzle can be required. American conventions on rifle barrels are extremely heavy for the lightweights, with the exception of Kimber.

https://www.cip-bobp.org/homologation/uploads/ciptexts/a-4-1-en.pdf