Thread: Calculating pressures in hand loads

Hey team,

Is there a way to calculate pressures in your cartridge for hand loads? I know each cartridge has it own “maximum pressure” and load data lists a “maximum load” but how do they actually come up with these figures. I know a few people who load higher than the max load for their specific powder and the cases show no pressure signs. Is this a pointless exercise or is it a viable piece of information that can be used to perfect loads?

Cheers, 7RMBoy

Google it or read any good reloading manual like sperr or lyman or hornady internal ballistics.

I'm using Gorden Reload Tools to estimate the pressure and velocity.

There is no substitute for a chronograph. Buy one.

Originally Posted by 7RMBoy

Hey team,

Is there a way to calculate pressures in your cartridge for hand loads? I know each cartridge has it own “maximum pressure” and load data lists a “maximum load” but how do they actually come up with these figures. I know a few people who load higher than the max load for their specific powder and the cases show no pressure signs. Is this a pointless exercise or is it a viable piece of information that can be used to perfect loads?

Cheers, 7RMBoy

Pressures in reloading manual are not calculated they are measured using specialist equipment, and they are really only relevant in the barrel/chamber they were fired in.
There are programs that can estimate pressure's, but they are just that an estimation and should not be relied on. they don't take into account what primer you use, your paticular batch of powder, free bore in your chamber, condition and exact is and number of grooving in your barrel, etc.
This is the reason that quite a lot of reloading manuals loads are considered conservative.
There are ways to judge pressure that the experienced hand-loader can use but these take time to learn and can be unique to each rifle.

Greetings 7RMBoy,
Congratulations, you have asked one of those questions to which there are many answers. In short there are ways to estimate pressures but not to calculate them. Most manuals these days do not include pressures for the loads but are developed using pressure testing equipment. Years ago some manuals had data that was not pressure tested but worked up by looking for pressure signs. Some of this is fire cracker hot and should not be used. Current manuals should keep you out of trouble most of the time as long as you only use the data for the projectiles it was developed for. As an example do not use data for jacketed projectiles in loads for the solid copper projectiles.
I would suggest that you look at the manuals for both the powder and projectile you are using and use these as a guide. There is quite a bit available on the interweb. I tend to use the Hodgdons (ADI) and Nosler data. The Nosler data seems to a bit hotter (sometimes ) than Hodgdon. I use a chronograph to validate the data and pick up any changes in powder speed from lot to lot. Handloading is a fascinating pastime and you never stop learning.
Regards Grandpamac.

Cheers grandpamac,

Great reply. Have just loaded my first batch of reloads ranging from Noslers minimum to their maximum to try get a feel for which amount of powder works best. The question more originated from seeing something about seating depths affecting chamber pressures.

Originally Posted by 7RMBoy

Cheers grandpamac,

Great reply. Have just loaded my first batch of reloads ranging from Noslers minimum to their maximum to try get a feel for which amount of powder works best. The question more originated from seeing something about seating depths affecting chamber pressures.

Greetings Again 7RMBoy,
Yes seating the projectile closer to the rifling does increase pressures and velocity slightly. The greatest effect is with cartridges like the Weatherby magnums that usually have a free bored chamber (long way to the rifling). I usually start with the projectile seated 1mm from the rifling, where I can, and have seldom needed to change that. Barnes projectiles need to be seated at least 1.25 mm (0.050 inches) from the rifling and further often works best. I doubt if you will have any problems unless you set the projectiles hard into the rifling and probably not even then.
Regards Grandpamac.

It has been done with pressure test barrels. Back when engineers wore pocket pen protectors and used slide rules there was a great deal of this done as research. Really old Manuel's often had a section on the physics aspect of propulsion.
These are two graphs from such a book. Progression means distance down the barrel of the bullet.
It may not add anything to the discussion but it is interesting.

Cheers for tha mimms2, that clears a lot up

if you get flattened primers and/or sticky bolt or brass flowing into ejector hole/marks on rear of case you are WAY OVER do not progress any heavier load..pull any you have loaded.
I personally DONT use a cronicgraph....Ive loaded for my own rifles for years and have good feel for whats getting hot,in mine....each rifle is different.
any of the OLDER /EARLY manuals have good info on this.

I haven't tested these methods, but they may be of interest:

Simple Trick for Monitoring Pressure of Your Rifle Reloads | Hodgdon Reloading

https://www.shootingtimes.com/editor..._200906/100088

primers ARENT irrelevant.....BUT they can be misleading if you dont know what your looking for....MOST older manuals have photos to show a fella what looks too hot...yes different primers react differently thus modern thinking they no good as indicater....
I do believe you will agree if your primers are flat/cratered/popped out of pocket/sooty/ruptured you have an issue and need to stop shooting and work out whats going on....IF primers WERE irrelevant you telling me you just carry on with any and all the above happening???dont think so,therefore they ARE relevant.