What determines how much pressure a cartridge can handle?

**jdvisagie** · 10-02-2017, 10:33

Hey guys,
Been wondering for a while what determines the amount of pressure a particular cartridge can safely handle. Looking a list of cartridges and their "safe operating" pressures, I see that most CF rifle cartridges fall between 45-65k psi (SAAMI).

However, lets say 2 different cartridges - one low (30-30) and the other high (300 WSM) safe pressures using the same specced rifles - same thickness barrel & lets say k98 actions - why can the one handle more pressure then the other?

Surely the chamber and action is what holds everything together?

Some quick googles didn't give me a clear answer...
If some insights from the clever peeps will solve this for me I can sleep soundly again..

**treeman** · 10-02-2017, 10:45

The design of the action and chamber mostly and secondly the design and type of cartridge. Some old cartridges are of balloon head design and weak, some old cartridges are of sound design but in a weak action. Some old cartridges can be rediscovered in a modern action(read steel) that can handle higher pressures than the steels at time or the action/bolt design of that era , like the 30 30 and all those old Gov Mod 40-70, 40-? .
The chamber pressures for some rifles are still listed as that of black powder times.Not yet updated

**Steve072** · 10-02-2017, 11:11

As treeman says action types - sometimes manufacturers will load for the weakest possible action, e.g. old 30-30s. The brass thickness will also vary between the old and new calibers generally thicker on modern cartridges.

**The Beast** · 10-02-2017, 11:20

It is so that the older rifles chambered in that cartridge will be able to safely fire it.

This is the reason the 357 was developed. With the advent of smokeless you could do a lot more with a 38special case but the guns that were chambered in 38 could not safely withstand the higher pressures thus they made the case longer and now you have all the benefits of the 357 pressures and you can still fire 38 ammo.

I regularly load 38spec cases to 357 pressures to shoot in 357 guns. I have 38 chambered guns as well but I make sure my COL for the 357 loads does not fit in the 38.

**jdvisagie** · 16-02-2017, 15:48

Thanks for that guys..

**zakiwi** · 22-02-2017, 09:52

I think if the actions/chambers were the same, tgen it would come down to brass thickness, and I suspect you'd find that the older cartridges were a lot thinner.

**The Beast** · 22-02-2017, 14:38

Originally Posted by zakiwi

I think if the actions/chambers were the same, tgen it would come down to brass thickness, and I suspect you'd find that the older cartridges were a lot thinner.

The chamber and bolt is what holds the pressure.

The brass holds everything together (primer, propellant and bullet)

The side walls of the cartridge has 2 main functions. First is to seal against the chamber to ensure that no gas escapes through the back of the chamber. For this it needs to be malleable enough to expand fast enough without to much resistance thus it is rather thin and cant stand much unsupported pressure. Also needs to have enough elasticity to spring back and not bind in the chamber. Secondly to be strong enough to withstand handling, cambering and extraction.

The back of the cartridge also has 2 main functions. First is to house the primer and case rim. The other is to withstand the pressure where the case is unsupported. This is more in handgun chambers. Rifle cases tend to be better supported. The unsupported sections are also relatively small as the brass cannot withstand high pressures. This is also why the bulk of the brass is at the base of the cartridge.

Cartridge operating pressures is determined by the chambers they were designed to be used in. The weakest chamber/bolt is the top end of that cartridge.

As I mentioned above. The 38special case can take much higher pressures (when used in 357 chambers) but the 38spl guns can't work on those pressures.