The change in chamber pressure

[38magnum]

I have been doing digging through alot of loading manuals while killing time on my next gun purchase.

I know that when the model 19 started having visible issues with the use of 110 and 125 grain jhp loads, SAAMI made a second 35,000 PSI pressure level for 357 magnum.

The old 43,000 was kept, and still used mainly by CIP. America uses the 35,000. Although to be honest after perusing the old lyman manuals, the modern 357 loadings seem to be using the 25,000psi "general purpose, low powered" loadings as far as bullet wieght and velocity instead of the lyman "heavy duty large frame" magnum loads.

Hasnt anyone noticed that many of the old heavy duty loadings for 38 special and 357 magnum, are actually being used to push identical weight JACKETED bullets instead of lead bullets now?

 

[ReloadforFun]

The change in pressure was the result of changing from the old CUP system to piezoelectric transducer equipment. No pressure changes were planned, but with the CUP system all you have after the shot is the copper cylinder (crusher) with a new length. The length is measured and then a tirage table compiled for those crushers consulted to translate to the amount of pressure that would yield the length measured.

The transducer can show the entire pressure event. What was seen with, particularly, the 357 Magnum (and some other cartridges, was that there was a pressure spike. The spike is extremely short duration, but no one was explaining it.,

The pressure was changed so that the pressure spike did not exceed the originally planned pressure (some 45,000 psi or such) resulting in the current 35,000 psi MAP for the 357.

Im have not shot 357 in some time, and then mostly reloads. The factories have normally tried to load near the SAAMI MAP value (without exceeding it), so given the different in the specs between ther 38 and the 357 they should be different. Only you, your gun and a chronograph can be the determining factor (unless you have a pressure gun handy).

 

[38magnum]

The change in pressure was the result of changing from the old CUP system to piezoelectric transducer equipment. No pressure changes were planned, but with the CUP system all you have after the shot is the copper cylinder (crusher) with a new length. The length is measured and then a tirage table compiled for those crushers consulted to translate to the amount of pressure that would yield the length measured.

The transducer can show the entire pressure event. What was seen with, particularly, the 357 Magnum (and some other cartridges, was that there was a pressure spike. The spike is extremely short duration, but no one was explaining it.,

The pressure was changed so that the pressure spike did not exceed the originally planned pressure (some 45,000 psi or such) resulting in the current 35,000 psi MAP for the 357.

Im have not shot 357 in some time, and then mostly reloads. The factories have normally tried to load near the SAAMI MAP value (without exceeding it), so given the different in the specs between ther 38 and the 357 they should be different. Only you, your gun and a chronograph can be the determining factor (unless you have a pressure gun handy).

not soo true good sir..

over on the ruger forums there is a good thread in which it was proved that the SAAMI level for 357 magnum was dropped at smith and wesson request when the modern police loads in 110 and 125 grain bullets started kiling magnum k frames.

We all know the debate, the first thought was bullet weight and bullet length and powder flash in the gap. now its converted to TYPE of powder and how that powder type acts like high speed sandpaper..

Lyman used ot have two levels for 357 magnum. a large frame level that STARTED at 25,000 psi and ended at 43-45,000 psi. and a standard easy shooting good for any magnum gun that maxed out at 25,000 psi.

Also had two sections for 38 special. the hi vel for large frame/heavy duty and the standard loads. However, the standard load section is still delivering higher velocities with 158 grain bullets than modern standard 38 special.
1950s lyman 158 grain fatory 38 special duplicate load was hitting 856 fps in an actual model 15.

SInce teh peopel who wrote those manuals are dead.. its hard to understand what the max pressure for the hi vel loads for 38 special were. But most people here on THIS forum consider 38-44 smith and wesson to top at 25,000.

so thus the 38 special j frame in the 1950s smith and wesson ad was rated and safe to use 38-44. so thus technically it should mean the K frames were capable of taking more.

Sure i have seen photo copies of memos from smith and wesson to police departments approving the use of the 38-44 ammo in model 15 but giving a more in depth inspection process for the guns shot with it. Like a 500 round detail inspection, and a mandatory "return to factory" when they fired 1,000 rounds

 

[ReloadforFun]

That was the way an ammunition manufacturer explained it to me.

 

[alwslate]

The old CUP standard for the heavy frame .357s was 46,000 CUP but most loading manuals did not list loads for all revolvers that were in excess of about 43,000 CUP. When the change was made to PSI standards the limit for all revolvers became 35,000 PSI. From Brian Pearce's data of pressure tested .357 loads it is obvious that 35,000 PSI and 43,000 CUP load data are about the same.

 

[stansdds]

Yes, the big published pressure value drop from 43,000 or 46,000 to 35,000 was the difference between copper crusher pressure measurements (CUP) and Piezo-electric sensor pressure measurements (PSI). Before you ask, no, there is no mathematical formula to convert between the two as the two are entirely different measurement systems.

 

[WR Moore]

Back when, the Speer website had a detailed description of the differences between the copper crusher system and piezo electric pressure measurement systems. They also went deep into the weeds on +P. Unfortunately, I assumed that information would always be available.

Short version: at and below 17,000 copper crusher & piezo are the same. Above that point, there's no relation as stansdds states. Once you get into rifle pressures (>50K?) they can be mathematically related.

Somewhere I've got a load manual where they explain that certain charge weight reductions aren't mistakes. The changes are the result of previously unknown pressure spikes once piezo electric pressure testing was in use and time/pressure curves could be established. More recently (relative term), the FBI noted excessive pressure spikes in some .40 S&W 180 gr ammunition. They then changed their issue ammunition to 165 gr to avoid those pressure spikes.