Understanding cartridge efficiency

Stiltsville

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Has any chamber pressure testing been done on any wildcats. I have read that for an Ackley the only way to achieve higher velocities the chamber pressure must be higher. This is what I wish I had the money to do. Truly test chamber pressure between wildcats and parent case. Also cutting the wildcat back until I have equal volume in both cases ( parent and wildcat) and see how they perform. Anyone want to pitch in a few thousand.😜
Why waste the money ?

If you create a "wildcat" say AI style from say a 308 case, that has the same internal capacity as the base 308 and load them up with identical components, shoot them in "twin" rifles, their velocity will be the same. It's basic physics.

The fact that many AI cartridges show little advantage in velocity when using the same powders as the parent, gives you a hint at what your experiment would produce. AIs that work hold more powder and run at higher pressures than the parent.

You might wish to acquire Fred Zeglin's two books on the subject.
 

bigngreen

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Why waste the money ?

If you create a "wildcat" say AI style from say a 308 case, that has the same internal capacity as the base 308 and load them up with identical components, shoot them in "twin" rifles, their velocity will be the same. It's basic physics.

The fact that many AI cartridges show little advantage in velocity when using the same powders as the parent, gives you a hint at what your experiment would produce. AIs that work hold more powder and run at higher pressures than the parent.

You might wish to acquire Fred Zeglin's two books on the subject.
Exactly, why waste the money when you can just pull stuff of the internet, much better than actually doing it!!
 

antelopedundee

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Oct 14, 2018
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Iowa
Has any chamber pressure testing been done on any wildcats. I have read that for an Ackley the only way to achieve higher velocities the chamber pressure must be higher. This is what I wish I had the money to do. Truly test chamber pressure between wildcats and parent case. Also cutting the wildcat back until I have equal volume in both cases ( parent and wildcat) and see how they perform. Anyone want to pitch in a few thousand.😜
A place like Hodgdon would load the AI version until it reached a pre-determined safe pressure which if you look at their data is usually something between 62,000 and 63,000 psi. Whatever velocity you get from that compared to the parent case is your improvement. It may or may not be worth the effort to you. If pressure signs like primer appearance and bolt lift allow it, you could try inching up higher. Also your second point has been answered here a dozen times. Cutting the wildcat back to match the volume of the starting case gets you nothing in extra velocity over the parent case. Shape doesn't matter.
 

Stiltsville

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You have a serious reading comprehension issue, I own pressure testing equipment, I know what I know because I've used the equipment, chambered the barrels and pulled the trigger.
Thanks. can you publish your results proving that a case shaped differently, with the same capacity, in the same caliber, with the same load, in a twin rifle produces different velocity for our edification ?
 

Bart B

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Dec 25, 2005
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I was looking for an official case volume/capacity in grains or milliliters of water.
I've never seen any official case capacities listed. Too many variables across all of a given cartridge.

The only way one would be valid is to have the case outside dimensions at some standard. SAAMI cartridge case specs for instance. Otherwise, fired cases and resized cases would have different inside volumes. Out of round cases have less capacity than perfectly round ones.

To say nothing about case weight. A 40 or 50 grain spread in case weight makes a difference.
 
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Stiltsville

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Here's a start.







 

antelopedundee

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Iowa
I've never seen any official case capacities listed. Too many variables across all of a given cartridge.

The only way one would be valid is to have the case outside dimensions at some standard. SAAMI cartridge case specs for instance. Otherwise, fired cases and resized cases would have different inside volumes. Out of round cases have less capacity than perfectly round ones.

To say nothing about case weight. A 40 or 50 grain spread in case weight makes a difference.

For the 6.5-06 A Square, QuickLoad gives Useable Case Capacity: 60.456 grain H2O = 3.925 cm³ Where would they have gotten that from?
 

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