LongShot Pressure Curve This was Split from the History topic.

[Mike_Fontenot]

Interesting how peaked that curve is ... i.e., how small the average pressure is, compared to the peak pressure.  I would have hoped that ways would have been found to control the burn rate so that the pressure is nearly constant over most of the bullet travel ... that would obviously be the way to get the highest muzzle energy for any given max pressure.

I did an interesting (at least to me) calculation recently:  if you take max pressure to be 37,500 psi, and assume that the pressure is constant at that level for the entire 4.25 inch bullet travel, then the force on the 0.4" diameter bullet is a constant 6000 lbs.  That then gives a muzzle energy of 2125 ft-lbs.  The hottest loads are only about a third of this value, so that calculation told me that the average pressure being achieved is only about a third (at most) of the max pressure.  I suspect that the reason an almost constant pressure isn't being achieved is that it would be difficult to control, and would thus be too dangerous to use.

[The_Shadow]

Mike, I decided to split this out of the 10mm History which is the sticky as such...this way we can openly discuss this as its own topic.

This screen shot was done for me by a person who had the QuickLoad Program.  I wish others who may have this program would run the numbers to see if this still brings the same numbers to the screen.

That data at 9.4 grains of LongShot under the Hornady 200 XTP was what Mike Willard of SwampFox Ammo used in the 1240 fps loaded rounds.

SwampFox also had a 10.0 grain loading @ 1325 under the Hornady 200 XTP, I'd like to compare those numbers as well.  Many saw serious bulges and smiles depending on the guns and setup they were using.

Anyone with the QuickLoad Program please chime in and please run some numbers to verify the findings. 

[475/480]

On my QL program the numbers are : Using the Hornady 200gr XTP
Longshot 9.4gr @ 1.260" OAL : PSI = 59,743  @  1295 fps
Longshot 10.0gr @ 1.260" OAL : PSI = 71,549  @ 1359 fps


Sean

[Mike_Fontenot]

On my QL program the numbers are : Using the Hornady 200gr XTP
Longshot 9.4gr @ 1.260" OAL : PSI = 59,743  @  1295 fps
Longshot 10.0gr @ 1.260" OAL : PSI = 71,549  @ 1359 fps

On the wikipedia page for 10mm auto, it shows (as I recall) a max pressure of 37,500 psi.  Does the "max pressure" spec actually specify what the maximum peak pressure is, on the pressure versus bullet position curve (or perhaps what the average of the peaks is, over multiple trials)?  If so, the above pressures are WAY over spec ... right?

[Yondering]

  I suspect that the reason an almost constant pressure isn't being achieved is that it would be difficult to control, and would thus be too dangerous to use.

The reason is that a powder doesn't exist that could give constant pressure through the whole barrel. And, if it did, max pressure would have to be lower. And muzzle blast would be tremendous.

That pressure curve shape is typical of all modern smokeless cartridges; nothing out of the ordinary here (other than the over-max peak pressure).

[The_Shadow]

Thanks for the numbers Sean...   You numbers mirror what I was sent as posted...

Just how accurate does Quickloads compare to a actual pressure test?  Copper Crusher (CUP), Piezoelectric transducer and Strain Gauges (PSI)

SAAMI Pressure testing info...
http://www.saami.org/specifications_and_information/publications/download/205.pdf

Example of 205 10mm pressure MAP
The specific loads of the test have to fit the MAP set by SAAMI.

Here is a typical MAP as set by SAAMI
Nominal Mean Instrument @ 15 feet with =/-90 fps from test barrel
Maximum Adverage pressure MAP of 35700 psi
Maximum Portable Lot Mean MPLM of 38700 psi
Maximum Portable Sample Mean MPSM of 40500 psi

The ammunition in test (10 rounds) would need to fit this established profile.

Nothing in the sample over 40500 psi

Here is something to consider...The piezoelectric transducer system employs the transducer flush mounted inside the chamber of the test barrel. Pressures developed by the expanding gases to the cartridge walls causing the transducer to deflect creating a measurable electrical charge. This change is then converted to a pressure reading in psi.

Strain Gauge Systems being sold are being used on the outside of the chamber of the test barrel. The expanding cartridge is not directly acting upon the transducer as in the SAAMI testing.

Original NORMA loadings were above the upper SAAMI 40,500psi and closer to 44,400 psi