From: gmk@falstaff.MAE.CWRU.EDU (Geoff Kotzar)
Subject: Re: 9mm +P ammo
Organization: Case Western Reserve University

In article <1992Aug19.002356.21931@smartstar.com> smrtstr!syspb@uu.psi.com (Paul) writes:
#What the heck is a 9mm +P load?  I read some posts where people mention
#it, but my reloading manual doesn't mention it.  I've never seen any
#9mm +P ammo in the store either.  I have seen 38 special +P ammo before.
#The maximum working pressure for the 9mm is 35,000 CUP.  Does this mean
#that the 9mm +P load excedes this limit?
#
#On a different subject, it seems like every time a new reloading manual
#comes out, the maximum powder loads get lower for the 9mm.  An older
#Speer manual says you can use 10.2 gr of Blue Dot with a 100gr HP bullet.
#A newer manual says that the maximum is 9.7 gr.  I've noticed this with
#other manuals too.  Would this 100 gr HP bullet be considered a +P load?
#These manuals probably are lowering the values for safety and liability
#reasons.  I've asked gunsmiths about reloading, and most of them won't
#even talk about it.  I guess they don't want to get sued by giving bad
#advice.  The publishers of the manuals probably feel the same way.

There is an additional factor that comes into play here. That is product
specifications can change over time. Remember the disclaimers concerning
this very point: specifications may change without notice. Speer's data
is generated with Speer's bullets and those manufactured when manual #11
was in production are not necessarily identical to the "same" bullet made
when manual #9 was being produced 10 years earlier. Any or all of the
design parameters may differ: core hardness, jacket hardness, jacket
thickness, diameter, seating depth, ect. These will have a direct effect
on the allowable maximum powder charge.

Also, maximum load criteria can change. And I don't mean liability here
but rather  older manuals may not have listed loads developed with pressure
guns but rather commercial firearms. Sierra and to a certain extent Nosler
still do not use pressure barrels.  Also maximum loads depend on the current
crop of firearms available for a cartridge. A specific example is the .357
Magnum. Prior to the introduction of the K-frame S&W's the .357's were loaded
up to the allowable maximum pressure of 46 KCUP. The K-frame guns would not
tolerate a steady diet of ammo at this pressure level and the pressure level
was of the factory ammo and many reloading manuals was reduced to as low as
32 KCUP (DuPont and Lyman). The latest Lyman manual now lists loads for the
.357 that run the full 46 KCUP again. Liability is not the only reason for
the variability of the data.

geoff kotzar