Befuddled by pressure

[DR. Furlicker]

I’m having a hard time understanding maximum load pressures.
For example when I look at the Hodgdon load data it shows the max load for a 55 gr. spr sp using 21gr of H4198 to produce a velocity of 3150 and pressure of 47,000 CUP.
For the same bullet it shows using 25.3gr of H335 to produce a velocity of 3203 and pressure of 49,300 CUP.
My question is if the case and chamber can safely handle 49,300 CUP with H335 why is it dangerous to go above 47,000 Cup with H4198?

[10 Spot Terminator]

Here is what little I understand on this,,,

although the pressure listings for the max loads may be lower for a paricular powder their burn rates tend to have an optimum operating range and when at the top of their listed charge weights the powders become a bit unstable and are subject to erratic pressure jumps . Much of this same principle can be verified with a chronograph when you are working up loads and tend to see wider extreme spreads in your bullet speeds. Remember they test these loads with heavy actions in a lab and if something goes wrong they arent using their face for a backstop .
Stay Safe, 10 Spot

[steve4102]

The pressure listed is usually "Average" pressure. Pressure is not constant from beginning to end and will have High and Low points. Even though avg pressure may be less the actual "Peak" pressure may be higher.

[SL1]

Actually, the pressure limit is on the peak pressure, not the average pressure over the duration of a single cartridge firing.

However, the peaks of several separate cartridges are averaged to compare to the industry limit.

I am not familiar with the actual statistics used to decide when to stop adding powder. There are several possibilities, and it seems that different statistical methods may be used for the older copper crusher and the newer electronic measuement methods. But, "10 Spot" is basically correct in saying that the top load shown may not quite reach the industry pressure limit because the spread in the pressure peaks for a bunch of cartridges indicates that any higher loads have some unacceptable probability of exceeding the pressure limit with individual cartridges.

If somebody has a copy of the SAAMI standards that specify the statistics, it might be interesting to post that (or a link to it) here.

SL1

[steve4102]

Sporting Arms and Ammunition Manufacturers' Institute PSI Recommendations

The following list represents the Maximum Average Pressure (PSI) recommended by the Sporting Arms and Ammunition Manufacturers' Institute.

--------------------------------------------------------------------------------
Handgun Rifle
25 Auto 25,000 22 Hornet No PSI Std.
32 S&W Long 15,000 222 Remington 50,000
380 Auto 21,500 223 Remington 55,000
9mm Luger 35,000 22-250 Remington 65,000
9mm Luger +P 38,500 220 Swift No PSI Std.
38 S&W 14,500 223 WSSM 65,000
38 Auto 26,500 243 Winchester 60,000
38 Special 17,000 6mm Remington 65,000
38 Special +P 18,500 257 Roberts +P 58,000
38 Super Auto +P 36,500 25-06 Remington 63,000
357 Sig 40,000 260 Remington 60,000
357 35,000 6.5 x 55 Swede 45,000
357 Remington Max 40,000 6.5 x 284 No PSI Std.264 Win Mag 64,000
40 S&W 35,000 270 WSM 65,000
10mm Auto 37,500 270 Winchester 65,000
41 Remington Mag 35,000 7 x 30 Waters 45,000
44 Special 15,500 7mm - 08 Rem 61,000
44 Remington Mag 36,000 284 Winchester 56,000
45 Auto 21,000 7mm Mauser 51,000
45 Auto + P 23,000 7mm WSM 65,000
45 Long Colt 14,000 280 Remington 60,000
454 Casull 65,000 7mm Rem Mag 61,000
480 Ruger 48,000 7mm Wby Mag 65,000
7mm STW 65,000
7mm Rem Ultra Mag 65,000
30 Carbine 40,000
7.62 x 39 45,000
30-30 Winchester 42,000
303 British 49,000
300 Savage 47,000
308 Winchester 62,000
300 Rem Short UM 65,000
300 WSM 65,000
30-06 Springfield 60,000
300 H & H No PSI Std.
300 Win Mag 64,000
300 Wby Mag 65,000
300 Rem Ultra Mag 65,000
8mm Mauser 35,000
8mm Rem Mag 65,000
32 Win Special 42,000
338 Win Mag 64,000
338 Rem Ultra Mag 65,000
338 Lapua No PSI Std.
375 H & H 62,000
375 Rem Ultra Mag 65,000
416 Rem Mag 65,000
444 Marlin 42,000
45-70 Government 28,000