Pressure of 308 & 30 06


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Robert101
June 21, 2012, 11:00 PM
According to SAMMI pressure standards the 308 cartridge has a max pressure of 62,000 and the 30-06 has a max of 60,000 PSI. Now that is a 3.33% increase to the 308 Winchester. Yes the case is smaller, and therefore more propellant can be placed in the 30-06 case. So, why is the 30-06 pushing on average a bullet of similar weight about 100 to 150 FPS faster?

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Kachok
June 21, 2012, 11:06 PM
Larger case, more slower burning powder, that has been the magic for pushing bullets faster since the early 1880s

Robert101
June 21, 2012, 11:12 PM
Ok, but if we reverse the logic and say larger case, more powder but lower pressure - does that create more speed? It seems to just on the surface without any math. How does pressure relate to speed?

Ridgerunner665
June 21, 2012, 11:24 PM
There is more than just pressure in play here..."time" has to be figured in (length of the pressure curve) which is a result of how fast or slow the powder burns as well as how much powder is used.

Slower powders generally give more speed (longer pressure curve)...but if you go "too slow" the powder doesn't wanna burn right because there is not enough pressure to keep it burning.

Fast powders will burn...but by their fast burning nature, their pressure curve is pretty short.

The max peak pressure (for a given round) of both types of powder is the same...but the slower powder will still be pushing the bullet when the fast powder has ran out of steam.

Kachok
June 21, 2012, 11:29 PM
You cannot compare the pressure of the 308 to that of the 30-06 because the 06 can maintain more pressure longer thanks to the higher volume of powder. Making 100,000psi of pressure for 4" of travel will not outperform a bullet making 50,000psi for 18" of travel. The old 6.5x55 can outperform the modern high pressure 6.5x47 because of the higher case capacity. We see that many times in firearms. High pressure cartrages do tend to be more powder efficient though, meaning they generate more speed per volume of powder used .25 WSSM and 257 Roberts for example.

ArchAngelCD
June 22, 2012, 01:35 AM
Like said above, slower powders will push heavy bullets very fast. not many would consider using H4350 in the 308 but it's my most used powder in the 30-06. That's my story and I'm sticking to it! :D

Ridgerunner665
June 22, 2012, 01:45 AM
I used to use Reloder 19 in the 308...it has a nice "crunch" when you seat the bullet :D, was decently accurate with good speed too...

You don't see it listed for 308 in load manuals anymore though :confused:

EDIT: H4350 and Reloder 17 are pretty similar....hmmmm! (no load data to support the idea though)

Kachok
June 22, 2012, 08:13 AM
Nobody lists RL19 because it burns too darn slow, (says the man who uses compressed loads of RL22 in his 06 :D ) RL 15 or 17 is more in the range of the 308 with 165-180gr bullets

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