Found this 9mm Luger ammo vs 9mm

[Patrick Sweeney]

Just to add a bit more confusion, the 9mm case, since it is tapered, may or may not headspace on the case mouth. The case is a cone, going into a cone-shaped hole. When the two cones meet, the case stops, whether the case mouth has reached the front of the chamber or not.

And Kyrie, where did those pages come form Did the Army really print technical data on 9mm cartridges that lists the bullet weights as 182 and 179 grains?

Finally, the MAP, Maximum Average Pressure, is a ceiling, not a goal. If an ammo maker can get the velocity they want, at a lower pressure, they will. So, if the goal is (for example) a 115 grain bullet, at 1,200 fps, and they can do it with the powder you have, at 27,000 PSI, then they'll do it.

[Kyrie]

Originally Posted by Patrick Sweeney

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And Kyrie, where did those pages come form

Technical Manual number is at top, right, corner of each page.

Originally Posted by Patrick Sweeney

Did the Army really print technical data on 9mm cartridges that lists the bullet weights as 182 and 179 grains?

No sir, they did not. But they did list the cartridge weights as 182 and 179 grains :-)

Originally Posted by Patrick Sweeney

Finally, the MAP, Maximum Average Pressure, is a ceiling, not a goal.

Correct. ANSI/SAAMI Z299,3 – 2015 “Maximum Average Pressure - is the recommended maximum pressure level for loading commercial sporting ammunition.”

Originally Posted by Patrick Sweeney

If an ammo maker can get the velocity they want, at a lower pressure, they will. So, if the goal is (for example) a 115 grain bullet, at 1,200 fps, and they can do it with the powder you have, at 27,000 PSI, then they'll do it.

Correct. Some people confuse the SAAMI MAP with a “service pressure”. That is not the case, and “service pressure” doesn’t even exist as a concept in SAAMI. Moreover, some people tend to equate higher peak chamber pressure with higher muzzle velocity. That may or may not be true in any specific case. Muzzle velocity and peak chamber pressure are only vaguely related, and in some cases may actually be inversely related. Peak chamber pressure is not a good predictor of muzzle velocity.

SAAMI has performance as the goal, with that stated performance to be attained without exceeding some stated average peak chamber pressure (“Maximum Probable Sample Mean"; MPSM).