CUP, PSI and how does the gun figure into it?

[Tommie]

This Daily Bulletin article re-sparked an old question for me.

http://bulletin.accurateshooter.com/2018/04/know-your-terminology-cup-vs-psi/

Are the 30-30 case pressure limits based solely upon the brass as designed with all other things being equal or are the typical 30-30 rifles it was originally designed for being taken into account? For example, if a Mauser (or other strong bolt action) where chambered in 30-30 would the safe pressure limit still be no different than SAAMI specs?

 

[watercam]

The 6.5x55 Swede is a case in point. The model 96 rifles were not quite as strong as the model 98s and were loaded to a lower pressure. The same cartridge in a strong, modern action enables a reloader to load up a little bit for more velocity. But only a bit. Brass strength is part of the equation as well.
Interesting that you would use the 30-30 as your example. No doubt many have hot rodded that cartridge (especially in bolt guns I would think)) but I am not sure an extra 100 fps is worth it with that cartridge.

 

[Tommie]

Interesting that you would use the 30-30 as your example.

The 30-30 PSI limits are mentioned in the article. Agreed that not many people have built hotrod 30-30 rifles. My personal interest actually is in the old Donaldson Wasp. Back in the day (whatever that means) benchrest competitors where running screaming hot loads in old Mausers. Pressure estimates of their old loads run closer to 60K PSI which would be well beyond the safe pressure limits of 30-30 brass according to SAAMI.

 

[retired]

quoting poor american stds for european rifles is not a good idea
6.5x55 swede is 55kpsi
30-06 is 60 kpsi
when swedes convert 96's to 30'06 they proof them at 55kpsi,, down from the cip 58.7
the saami 8x57 50 kpsi ,, how is the 96 not as strong in practical use

The 6.5x55 Swede is a case in point. The model 96 rifles were not quite as strong as the model 98s and were loaded to a lower pressure. The same cartridge in a strong, modern action enables a reloader to load up a little bit for more velocity. But only a bit. Brass strength is part of the equation as well.
Interesting that you would use the 30-30 as your example. No doubt many have hot rodded that cartridge (especially in bolt guns I would think)) but I am not sure an extra 100 fps is worth it with that cartridge.

 

[243winxb]

modulus of elasticity- Cartridge Brass-
Material is 70 copper/30 zinc with trace amounts of lead & iron , called C26000. Material starts to yield at 15,000 PSI when soft (annealed), and 63,000 PSI when hard.
Material yields, but continues to get stronger up to 47,000 PSI when soft, and 76,000 PSI
when work hardened. Modulus of Elasticity is 16,000,000 PSI. This means to pull a 1.000 inch long strip to 1.001 inch long induces a 16,000 PSI stress.
So if you pull a 1.000 inch strip to 1.005 inch long, you get about 76,000 PSI, which is the max obtainable.

Above from Olin Brass Co.

In a 30-30 T/C Contender, i pushed a 150 gr Sierra to 2000 fps in a 10" barrel with out problems.

For my old Win 94, the loading is a lot less. The action type does mean a lot. How strong is it.

When a fired case is hard to EXTRACT* brass is no longer springing back. This would be above maximum for that firearm.

Its best to find an accuracy load below listed maximums in a manual.

Edit*

 

[Bart B.]

How case rear ends are supported at the breech is also considered by SAAMI in setting pressure specs. Their baseline is the action type with some minimum case support at peak pressure thats typically used with the cartridge.

300 H&H Magnum was first spec'd about 40K cup, 50K psi, now 54K cup, 58K psi. Other large 30 caliber modern cartridges are spec'd 65K psi.

 

[Comrade Terry]

When a fired case is hard to eject

Extract.

 

[KMart]

There is a fellow on BRC that is shooting a 30-30 in SRBR. I have no idea of his loads, rifle and pressures but it seems that he does very well with it. If LH sees this, maybe he can clear it up a little.

 

[retired]

while it is based on a 30-30 case, and sort of looks like one, it ends there.
bolt gun, not a lever
shot in bench rest competition, and shot well.
i am sure he was shooting a little "warm".

There is a fellow on BRC that is shooting a 30-30 in SRBR. I have no idea of his loads, rifle and pressures but it seems that he does very well with it. If LH sees this, maybe he can clear it up a little.

 

[dellet]

Different cartridges will have different answers.

The same case that is used for the 30-30 when blown out to Ackley improved and countless wildcats, exceeds the pressures the case was designed and tested for. So chamber shape also plays a significant role.

One of the Ackley legends was his testing of the improved design in a model 94, with the saftey bar removed and the barrel unscrewed. No computer models, just a long string. Basically just the lever holding the action closed, the rifle held up.

The 25-35 has a history worth mentioning. Originally formed from 30-30 cases, after WW11 cartridge specific cases were made. They have a reputation for splitting necks when used to form other wildcats.

The 30-06 case was first used at blackpowder pressures using smokeless. From memory 1500 fps with a 150 grain bullet. Actions were improved to support the potential of the brass.

So as with anything related to shooting and hand loading, it depends on your set up.

 

[Tommie]

while it is based on a 30-30 case, and sort of looks like one, it ends there.
bolt gun, not a lever
shot in bench rest competition, and shot well.
i am sure he was shooting a little "warm".

30 Aardvark?

 

[retired]

no mike still calls it a 30-30, but you have to see all the work that goes into getting the case ready.

30 Aardvark?