Thread: Pressure Variations and Load Data

Greetings All,
Most of you have noted the reductions in load data for some cartridges over the last few decades. This was attributed to the more accurate electronic PSI pressure measuring system revealing variations in pressure not showing with the older crusher CUP system. I often wondered if these variations were in individual or different rifles. I was leafing through a back issue of Handloader and reading a Pet Loads article by Brian Pearce on the 7mm Rem Mag. Brian quoted a conversation with Alan Jones who edited the Speer Loading Manuals who reported wide variations, both higher and lower, in velocity in sporting rifles in 7mm Rem Mag compared with a SAAMI pressure barrel. These were in the order of several hundred fps. Brian reported wide velocity in sporting rifles as well. so there was my answer. It was the rifles.
So what does the average handloader need to know about this. Some will have noted that the max pressure of 61,000 PSI is lower than other magnum cartridges and published maximum loads are below that so an effort has been made to keep most of us out of trouble but there is still the chance that there are some rifles that may develop excessive pressure. My suggestion is to work up towards the max charges given chronographing the loads as you go. Do not go past either the max velocity or the max charge of powder. This should keep you safe.
As I type this I can hear a faint chorus of those who believe they can divine pressure by any number of methods but after close to fifty years of handloading and reading about it I have formed the opinion that the only useful method of pressure estimation requires a chronograph and good pressure tested data.
Regards Grandpamac.

Originally Posted by grandpamac

Greetings All,
Most of you have noted the reductions in load data for some cartridges over the last few decades. This was attributed to the more accurate electronic PSI pressure measuring system revealing variations in pressure not showing with the older crusher CUP system. I often wondered if these variations were in individual or different rifles. I was leafing through a back issue of Handloader and reading a Pet Loads article by Brian Pearce on the 7mm Rem Mag. Brian quoted a conversation with Alan Jones who edited the Speer Loading Manuals who reported wide variations, both higher and lower, in velocity in sporting rifles in 7mm Rem Mag compared with a SAAMI pressure barrel. These were in the order of several hundred fps. Brian reported wide velocity in sporting rifles as well. so there was my answer. It was the rifles.
So what does the average handloader need to know about this. Some will have noted that the max pressure of 61,000 PSI is lower than other magnum cartridges and published maximum loads are below that so an effort has been made to keep most of us out of trouble but there is still the chance that there are some rifles that may develop excessive pressure. My suggestion is to work up towards the max charges given chronographing the loads as you go. Do not go past either the max velocity or the max charge of powder. This should keep you safe.
As I type this I can hear a faint chorus of those who believe they can divine pressure by any number of methods but after close to fifty years of handloading and reading about it I have formed the opinion that the only useful method of pressure estimation requires a chronograph and good pressure tested data.
Regards Grandpamac.

Have to agree but you also need to factor in the US ability to sue for damages for any real or imagined transgression. You only need to read any owners manual published in the last 10? years to understand that red ink sales have gone through the roof to the extent that finding useful information is frustrating! I no longer use saami pressure figures, prefering to use cip which I find to be closer to real world pressures.

A big issue is "we" really only "see" US reloading data and gun writer witterings.

There is other data/information out there but it's hard to find in either print or internet form and is practically never in English, I've seen stuff in German and the Scandi languages, and I once saw a manual on the SA powders that was just so far away from US loadings for the likes of 375 H&H and 9.3x62 . . . .

There are now appearing in the US guys with their own pressure measurement equipment doing some interesting tests - I saw a utube video on 6mm ARC that was very interesting and had a sophisticated look at pressure data including just where the peak occurs etc.

None of this stuff (manuals, data, other people's loads etc etc) will ever replace the basics as GPM points out - work up, use and understand all the load is telling you.

"wiggle room" is a good thing..... if your loading to well below what the book says is maximum....it would take quite a few of them other factors to all be in play at same time before you would get close to harmful pressure levels.
playing things safe,is well......safe LOL.

Greetings,
Yes there is quite a bit of variation in data and some CIP pressures are way above SAAMI for European cartridges especially the military ones. There are pressure measuring set ups available. These used to have a strain gauge fixed to the barrel under the chamber but may have changed. The thing that was missing was the reference ammo needed to calibrate the set up and guarantee accuracy. The old maxim of garbage in equals garbage out applies. I almost exclusively use ADI powders and I would imagine the only data available for that comes from the US. It does not help when the speed of a powder is changed without notice as happened with AR2209 and likely may have happened with BM8208. Some of the data I have looked at is old like 1960's old and still offered without any warning. Data for the likes of the .30-40 Krag and .303 Brit are highly variable depending on the rifle they were worked up in. Once I get my A into G I should have some Krag loads to report.
Regards Grandpamac.

Originally Posted by grandpamac

Greetings All,
Most of you have noted the reductions in load data for some cartridges over the last few decades. This was attributed to the more accurate electronic PSI pressure measuring system revealing variations in pressure not showing with the older crusher CUP system. I often wondered if these variations were in individual or different rifles. I was leafing through a back issue of Handloader and reading a Pet Loads article by Brian Pearce on the 7mm Rem Mag. Brian quoted a conversation with Alan Jones who edited the Speer Loading Manuals who reported wide variations, both higher and lower, in velocity in sporting rifles in 7mm Rem Mag compared with a SAAMI pressure barrel. These were in the order of several hundred fps. Brian reported wide velocity in sporting rifles as well. so there was my answer. It was the rifles.
So what does the average handloader need to know about this. Some will have noted that the max pressure of 61,000 PSI is lower than other magnum cartridges and published maximum loads are below that so an effort has been made to keep most of us out of trouble but there is still the chance that there are some rifles that may develop excessive pressure. My suggestion is to work up towards the max charges given chronographing the loads as you go. Do not go past either the max velocity or the max charge of powder. This should keep you safe.
As I type this I can hear a faint chorus of those who believe they can divine pressure by any number of methods but after close to fifty years of handloading and reading about it I have formed the opinion that the only useful method of pressure estimation requires a chronograph and good pressure tested data.
Regards Grandpamac.

Hi Young fella......the bore will make a difference. I had a local .284 barrel that could never reach optimum velocity, and expanded primer pockets well before the desired velocity was reached. I converted it to a SAUM and it was significantly slower than a Kreiger cut barrel....SO be very careful when trying to get that magic velocity....pressure signs should be heeded before all else....!

If it is of any help, here you can find some loads from a German hunting forum. Some loads are even verified by our gun authorities. Translation should not be too difficult. you might have different powders though:
https://forum.parey-jagdausbildung.d...edatenbank.26/