View Single Post
Old January 14, 2012, 06:10 PM   #44
JohnKSa
Staff
 
Join Date: February 12, 2001
Location: DFW Area
Posts: 18,492
Quote:
...my main point that the SAAMI psi standard has seriously downgraded the older magnum rounds from what they were under the CUP standard.
I'm actually primarily addressing your claim, your main point, that SAAMI is weakening ammunition specifications. That's actually the MAIN focus of my objection to your assertion.
Quote:
I don't have any velocity measurements from .357 ammo manufactured in the 1930s/40s and shot in any 8-3/8" barreled revolvers.
That test has actually been done.

Handloading resources may have reduced their maximum loads over time due to concerns about liability and as new technical data has come to light, but Handguns Magazine ran an article in the August/September 2006 issue in which they tested some vintage ammunition (.38spl and .357Mag) vs modern ammo. The specs were very similar, no evidence that the modern stuff was watered down.

The apparent slow reduction in velocity began in 1977 when SAAMI put pressure push the ammunition companies to publish velocity figures for .38spl and .357Mag ammunition based on chrono information from 4" Vented test barrels instead of data measured using the longer unvented test barrels that were common before that time. As the different companies came into compliance over a period of years, the appearance was that the ammunition was slowly being reduced in power. In reality, there was no reduction in power, only a change in the testing procedure, and the change happened abruptly for each company. It's just that the companies didn't all comply at the same time.

In addition, the change from CUP to PSI muddied the water even more.
Quote:
OBVIOUSLY, the psi standard produces a much lower actual pressure than the CUP standard. Don't you agree with that?
Attempting to compare CUP and PSI numbers is very complicated because they don't actually measure the same thing. PSI provides an actual peak pressure measurement while CUP provides information about the area under the entire pressure vs. time curve.

There's not a conversion between CUP and PSI that can be applied accurately in the general case. It's not even universally true that one number will always be higher than the other for a given cartridge. Trying to compare pressure specs in CUP to pressure specs in PSI to make a case that SAAMI is progressively reducing the maximum pressure specs is not as simple as it seems. Here's some reading on CUP and PSI.

http://www.thehighroad.org/showthread.php?t=214412

From what I've seen, besides the fact that handloading resources (as opposed to SAAMI) may be becoming more conservative, the main reason that people believe that ammo power is being reduced comes from the fact that in the late '70s and early '80s the ammo industry gradually began publishing more realistic velocity figures.

Getting back to the original subject, it is wise to stick to published reloading data. Going back to vintage reloading manuals to find hotter loads isn't as safe as it might seem. There's likely a very good technical reason that the new data is different.
__________________
Did you know that there is a TEXAS State Rifle Association?
JohnKSa is offline  
 
Page generated in 0.06013 seconds with 7 queries