CIP variation of pressure limits between cartridges?

[Ray B]

Both CIP and SAAMI list the pressure that they have determined to be the maximum for that cartridge. The variation among different cartridges is as much as 25%. The only reasons that I've read for one cartridge being significantly lower than a similar cartridge are: the actions that use the cartridge was weaker, or that the cartridge was generally used in hotter climates (Africa) where the heat caused increases in the pressure. Examples of cartridges loaded to lower pressures are those commonly used in lever action rifles or double rifles. So if those are the only reasons for the lower pressures, what about someone that has a Winchester Model 54 chambered in 30-30? Or a 450/400 chambered in a strong boltaction and the load is not pressure sensitive. Do those pressure limits still apply? To know someone would need to know the criteria used by CIP and SAAMI in their selection of the maximum pressure for a cartridge. Does anyone know what the criteria (besides action strength and possible Africa use) is?

 

[SheepDog]

Every cartridge has a history and many different guns chambered for it. SAAMI suggested maximum pressures are typically safe in any gun that has been chambered for the cartridge. The venerable old 30-30 cartridge started life at the beginning of the smokeless powder era. The guns were not built like they are today and the metals used were very different. The SAAMI spec rounds can still be fired in those old guns. If you have a strong bolt action you could easily load to modern pressures and be perfectly safe with modern brass. Most reloading manuals have three loading sections for the 45-70 cartridge for just that reason. The older trap-door rifles use the very low pressure data because they were made for use with black powder. The heavier lever action rifles use a slightly higher pressure load and the highest pressure loads are used in the modern single shot and bolt guns.
You hear people say that the case is not made for the pressure but the case has less to do with holding the pressure than the chamber and locking method it is fired from. The old folded cases could not take modern pressures but modern any draw formed case will handle modern pressures if fired in a modern designed gun.

 

[Tommie]

+1. Well stated, sheepdog. The 3 load listings for the 45-70 is a perfect example of gun design being the limiting factor. I have two strong bolt action 30-30 rifles. The brass is happy despite loads that are above SAAMI pressures.

 

[DaveTooley]

SAAMI and CIP data is submitted by a manufacturer, take the Creedmoor line from Hornady for instance, then it goes through an approval/review process and then cataloged as a standard for the rest of the industry.

 

[Ray B]

So the basis of the pressure limitation is the recommendation of the manufacturer?

 

[DaveTooley]

Correct Also SAAMI is made up of representatives from industry. It self regulates so to speak and regulates is not the right word. Compliance is voluntary but obviously it's in everyone's best interest to comply.
I believe CIP approaches it a bit more formally.

 

[dellet]

Another place that a manufacturer's or SAAMI pressure would come in to play would be with semi-autos. A cartridge designed for use in a semi-auto will factor in cycling rate.

Building a semi-auto action strong enough to handle a 300 WM has proven a lot easier than getting one to cycle and leaving the brass intact on extraction.