Developing a load... from scratch, so to speak.

[wallenba]

I'm frustrated with trying to find a load for my K31. I've been using C.E Harris 2400 data, but would like to try something else. My 2400 is getting VERY low, not likely to get any soon. I have an Accurate mold for the K31 that drops them at 178.5 grains with Lyman #2. I have lots of AA 5744 and some SR-4759, as well as IMR-3031. I think all three would be good candidates.

Is there an instructional book or article on how to develop a load from start to finish. Getting a safe start is the thing. I can take it from there.

[Crusty Deary Ol'Coot]

"K31"?????????

Sorry. I've developed lots of loads over the years, and when you speak of "2400" it makes me think handgun but you then go on to mention 3031 and I begin to wonder.

Crusty Deary Ol'Coot

[wallenba]

"K31"?????????

Sorry. I've developed lots of loads over the years, and when you speak of "2400" it makes me think handgun but you then go on to mention 3031 and I begin to wonder.

Crusty Deary Ol'Coot

K31, Swiss army military bolt action rifle 7.5x55MM. C.E. Harris has developed a 'universal load' using 16 grains of 2400. http://home.comcast.net/~gavinsw/guns/castbulletmilitaryrifle.pdf
here. On page three he does give some equivalent start loads to 2400, one is 3031, but I'd really like to start with AA5744. Don't know a safe start for that though.

Yeah, 2400 is primarily known for handgun, but is useful for cast military rifle cartridges too. I just don't have much left.

[Larry Gibson]

Is there an instructional book or article on how to develop a load from start to finish. Getting a safe start is the thing. I can take it from there.

Most quality reloading manuals go to great lengths explaining how to work up a load from start to finish. I suggest for your purposes the Lyman Reloading Handbook 49th Edition would be a good place to start; Chapters 1 - 3. Lyman Cast Bullet Handbook #4, Chapter 13 will provide additional information specific to cast bullets. Load data for cast bullets is found in the data section of both. Use the starting loads for the 30-06 for your Swiss cartridge and work up from there.

Of course the Sierra, Hornady, Speer, Nosler, Lee and several other manuals also have detailed instructions on how to work up a load. I know in this day of "electrons" having a book on something is pretty "so like last century" but books do come in pretty handy now and then.

Larry Gibson

[Crusty Deary Ol'Coot]

Yep, like Larry says!

CDOC

[wallenba]

Nope, that's just taking a start load from the book and working it up. I can do that, do it all the time. I'd like to learn how the ballistician who loaded the first ever load for any cartridge, decides what kind of powder and how much, can safely be used to start with. None of the books really get into that. They just give you a start point with a given powder and bullet.

What criteria, formulas do they use? There must be a way to do it, because they did. I'm not going to just take a powder I have used in another cartridge and start guessing. There is practically no cast bullet data for the Swiss 7.5x55, for many of the more popular powders used in other military cartridges using cast bullets.

[HATCH]

I have been lucky and haven't had to build a load from scratch.

However if I were to do that I would look at the burn rate chart
http://www.reloadersnest.com/burnrates.asp

AA5744 is # 128 while 2400 is # 106

There is always google and youtube

https://www.youtube.com/watch?v=tesRvnA4v6s

http://castboolits.gunloads.com/showthread.php?100415-Why-is-the-K31-SWISS-lacking-Reloading-Data&p=1086188&viewfull=1#post1086188

[wallenba]

I have been lucky and haven't had to build a load from scratch.

However if I were to do that I would look at the burn rate chart
http://www.reloadersnest.com/burnrates.asp

AA5744 is # 128 while 2400 is # 106

There is always google and youtube

https://www.youtube.com/watch?v=tesRvnA4v6s

http://castboolits.gunloads.com/showthread.php?100415-Why-is-the-K31-SWISS-lacking-Reloading-Data&p=1086188&viewfull=1#post1086188

I think you get what I'm interested in. Lots of other factors would be inserted in the calculation too. Volumetric density, proportional density. Joules in heat. Newtons law, that bullet isn't going to want to move at first. Probably even a constant in there somewhere. What would be great is a computer program that we could type in the basics, and have it spit out a pressure curve.

[Larry Gibson]

Nope, that's just taking a start load from the book and working it up. I can do that, do it all the time. I'd like to learn how the ballistician who loaded the first ever load for any cartridge, decides what kind of powder and how much, can safely be used to start with. None of the books really get into that. They just give you a start point with a given powder and bullet.

What criteria, formulas do they use? There must be a way to do it, because they did. I'm not going to just take a powder I have used in another cartridge and start guessing. There is practically no cast bullet data for the Swiss 7.5x55, for many of the more popular powders used in other military cartridges using cast bullets.

If you read the fine print in the manuals you can get an idea how the "ballistician who loaded the first ever load for any cartridge, decides what kind of powder and how much, can safely be used to start with." The ballisticians look at the burning rate of the powder to be used, the case volume, the caliber and the bullet weight/design. They then look at a similar cartridge of the same or similar case capacity or a cartridge of smaller case capacity using a similar bullet and a similar powder in makeup and burning rate (flake, extruded, ball and double or single nitro). They look at previous load data of those and the start loads for such. Then you know what they do next? They take a SWAG (Scientific Wild *** Guess) and probably use the same "start load" for that similar cartridge.

That's why I suggested you use the start loads for the 30-06. You might also consider the .308W. There is a lot of load data for both of those. There is no magical "formula".

Larry Gibson

[MBTcustom]

I use Quickload, and a Chronograph.
Quickload gives me a starting point, but that is still carfully weighed against similar cartridges as a sanity check, because every now and then it does something really wonky and it's NEVER exact.
Once I have starting point that I believe to be safe, I shoot over the chronograph and compare to what the program predicted. I make changes to the input data to make the two match, then use it as a rough estimate of pressure as I work up.
I'm still learning how to use it, but it's a heck of a program for working up for a wildcat.

I have a feeling that being a balistician was something different than what most people think of. I doubt they tested loads by putting a rifle to their shoulder. They had a bench mounted rifle that was protected in a controlled condition and rigged with pressure reading devices (CUP). If they blew it up, then a new barrel was screwed onto the action (or a new action was installed) and the testing continued. Just another wonderful day at the office.

If you do some research on SEE (Secondary Explosive Events) you will stumble across an account of a European country that had a load that was about to go to press and be their standard military load, when it blew up the test gun.
Larry can probably speak more intelligently about that account, as they called Ohler and brought in their shooting lab to see what the heck was really going on.
Anyway, in amongst that account they give out quite a few details about the load developing process and the controlled conditions they do it in if you read between the lines.

[wallenba]

A list of case capacities for comparison is what I need then. The charts I found on line do not list the Swiss. A vague reference in one thread post gave one of 65 grains, no source cited. The 30-06 is 68, the closest to that. AA5744 is what I want to use with my 178 gr. bullet. I'll have to work up the confidence to try it.

We may not have access to the 'magic formula', but I'd bet it's out there. Humans are pretty smart, they can calculate the ephemeris to put a space probe in a free trajectory from planet to planet and slingshot them in new directions all on paper to program and it works. They can do this too.

[wallenba]

Okay, just Rube Goldberg'd a test. Filled my 7.5 Swiss and 30-06 Hornady modified cases each with AA 5744. Results mirrored (almost) the water tests I read about. These cases have the webs drilled out and threaded, so... extra volume, but we are just comparing here. 7.5 Swiss = 64.2 gr. , the 30-06 = 69.4 gr. by weight. Getting more confident.

[dtknowles]

A list of case capacities for comparison is what I need then. The charts I found on line do not list the Swiss. A vague reference in one thread post gave one of 65 grains, no source cited. The 30-06 is 68, the closest to that. AA5744 is what I want to use with my 178 gr. bullet. I'll have to work up the confidence to try it.

We may not have access to the 'magic formula', but I'd bet it's out there. Humans are pretty smart, they can calculate the ephemeris to put a space probe in a free trajectory from planet to planet and slingshot them in new directions all on paper to program and it works. They can do this too.

Sorry but a three body space mechanics problem is a lot simpler than a theoretical internal ballistics analysis. There are too many variables in the internal ballistics problem that are not well defined. Quickload or Powley ballistics computer use a parametric method to make internal ballistics calculations that can predict pressures for different powder charges. I don't know if Powley has been updated but I think original it only worked for IMR powders.

As an example of the complexity of the theoretical analysis, just imagine the model for burning of just a single grain of powder. What is the mass of the Nitroglycerin and Nitrocellulose in a single grain what is the shape of the grain, what is the surface texture of the grain, is it solid or perforated, does it contain binders or inhibitors how does the surface area change as a function of time, how much gas does it generate and at what temperature, how much radiation heat transfer verse convective heat transfer. If you have looked at a charge of powder you have probably seen that not all the grains are the same. They don't all light at the same time and we are still just talking about the powder charge, more stuff to model, Parametric analysis is much better than theoretical for a problem like this. You should get Quickload.

Tim

[wallenba]

Had not considered that Tim. I assumed the Chemist new how much energy was stored in his formula and how to get it out in a predictable way (propellant shapes). No rule of thumb to apply, and casting off of minor variables for a conservative base line?

I'll look a Quickloads, cost vs. use may negate that option for me.

[leadman]

I have found in reloading for cartridges that do not have data for cast and are in the same size range as the full size military cases I start at 16grs of powders like 2400, 5744, 4759, and 300MP. I then work up and usually end up from 18 to 20grs of powder. Harris used the same criteria for his "Load" as far as cartridge cases go. If I use Unique I start at 12grs.

[dtknowles]

Had not considered that Tim. I assumed the Chemist new how much energy was stored in his formula and how to get it out in a predictable way (propellant shapes). No rule of thumb to apply, and casting off of minor variables for a conservative base line?

I'll look a Quickloads, cost vs. use may negate that option for me.

Dutch

The propellant formulators do know what you were thinking they know but it is not a theoretical value it is a parameter the get from testing. They used to use a "Bomb Calorimeter" Burn a powder charge in a closed volume and measure the energy release (pressure and temp) as a function of time. If they would share this data with us we could develop our own starting loads, I doubt this data is available.

Tim

[Wayne Smith]

As you have seen internal ballistics gets very complex very quickly. I assume you are looking for a cast boolit load for your K31. The easy way is to realize that the cast boolit slides down the barrel much more easily than a condom bullet so that data is safe to use as is. You can extrapolate from data for bullets closest to your boolit weight. You will be in safe territory because boolit pressures are always lower due to that easier slide.

I typically start at the lowest published bullet load and check my barrel for leading after ten or so shots. Then it is a careful work up constantly checking for leading and accuracy.

Sierra lists loads for the K31 for a large variety of bullet weights.

[wallenba]

Thanks everyone. I learned a lot from each of you. I think I may have been thinking this was going to be more complicated. 2400 was so easy to use, I put off this effort until now, now that the shortage has forced me to deal with it. I did try many searches here and elsewhere, just did not stumble onto what I thought I needed to know.
The real impetus that got me moving was my new mold from Accurate molds. It is a no compromise, made just for the K31 it seems, mold. It allows for full forward seating of the boolit. No more hanging the lube grooves down below the neck into the fire.

Excess650, thanks for sharing your data. My K31's throat is typical, in that it is short. My rifle seems to have been fired little in it's lifetime. I'd even say it is like new as far as bore goes. It's a very nice one overall. It has no import marks, and may have come into the country some other way. I will start with the 21-22 gr you have working.