What specifically determines MAXIMUM grains (or load)?

[orpington]

I have a Lyman 44th edition Reloading Handbook, open to page 80, because I am reloading for .32-40. (Another question, feel free to answer, but not my MAIN question, is why is .32-40 not in the 49th edition, as it is far more common than .38-55, or .40-65, or several other rounds that ARE published in that edition??? Should have .40-65, .38-55, AND several others, in addition to, and not instead of .32-40, IMHO).

In any event, what exactly determines the maximum grains, other than the obvious--e.g., too much pressure, causing catastrophic destruction of the firearm? What I mean is, I loaded 16 grains of IMR 4227 behind a 170 grain Jacketed bullet, and it was very MILD when it came to recoil, there were no signs of excess pressure, etc. The maximum load for IMR 4227 is 16.5 grains, with a velocity of 1348 FPS. And yet, one could load 30 grains of IMR 4895, which yields a velocity of 1892 FPS, this being 544 FPS more than the maximum load listed using IMR 4227 powder.

So, what exactly determines this? I am NOT one to play with fire and use loads that are NOT published data, plus 16 grains of IMR 4227 in this Winchester 1894 carbine provides satisfactory accuracy. However, if I had to 'guess' it has something to do with IMR 4227 being much finer than IMR 4895, therefore, burning faster, and generating higher pressures. Am I correct here?

Is there a mathematical formula that determines all this?

 

[Longhorn 76]

The maximum is primarily restricted by pressure. The pressure is related to many factors: case volume, temperature, primer, bullet weight/diameter/hardness/bearing length, bore, headspace, etc.

If you have neither pressure equipment nor a chronograph, you are pretty much guessing, and would be wise to stick to the tables.

Or, you could go by the seat of your britches, and we can have fun with your post when you blow something up.

 

[orpington]

This is an academic question more than anything else, because, if you read my original post, I an NOT one to play around with OTHER than published loads (AND, I had a real DUD of a published load once, such that a .44 S & W Special load was not even powerful enough to enable to exit the barrel. A call to the manufacturer reveals that this particular load was no longer being published). However, in the above example, EVERYTHING is identical when it comes to components, EXCEPT for the choice of powder.

 

[Walkalong]

Burn speed of the powder is the difference you are asking about. The slower powder, 4895, can burn more powder releasing more energy because it is slower burning and reaches max pressure later than 4227.

Powder kernel size is only one factor in how fast it burns.

 

[FROGO207]

Different propellants burn at different speeds. Your thinking is good there. The two you use as examples are really different in their makeup. Each propellant has a set of criteria that the maker designs into it. What you are trying to do to get a good load in a particular caliber is find a propellant that fills the case as close to full as possible and when burned will give maximum velocity while not exceeding SAAMI pressure specs under varying temperature conditions. There are many choices that will work OK for a particular round (brass/volume and bullet weight) in that caliber, but usually one that works better than all the others. Generally you can look at case volume and grains volume equivalent with respect to pressure and velocity to get a good idea of how a specific load will perform. I like the Lee reloading books as they show what volumes are approximately the grain equivalents and go from high to low on the pressure of the load for both starting and MAX. They also show the velocity found as well. This will give you a starting point to find which propellant is more efficient and better to try. Your results may differ as you do not have the exact same components or the firearm they used but are really close in most instances. Did I help or confuse you.

 

[Longhorn 76]

I apologize if I offended you.
What they said.

 

[Grumulkin]

In any event, what exactly determines the maximum grains, other than the obvious--e.g., too much pressure, causing catastrophic destruction of the firearm? What I mean is, I loaded 16 grains of IMR 4227 behind a 170 grain Jacketed bullet, and it was very MILD when it came to recoil, there were no signs of excess pressure, etc. The maximum load for IMR 4227 is 16.5 grains, with a velocity of 1348 FPS. And yet, one could load 30 grains of IMR 4895, which yields a velocity of 1892 FPS, this being 544 FPS more than the maximum load listed using IMR 4227 powder.

1. You need the pressure low enough that your gun doesn't blow up or get damaged as you stated.

2. The cartridge components need to be able to withstand the pressure. Not all cases, for instance, are manufactured the same way and can take the same pressure.

3. You have to be able to fit the powder in the case. With some powders you can fill a case to the brim and the pressure is still low.

4. When you start out low in working up a load, groups will generally be large, get smaller as the load is increased and then start to get larger again. Even if the pressure is low, for me the maximum load is that which gives me optimal accuracy.

How fast or slow a powder is often seems to be mentioned as the big difference between powders. I'd like to point out that there is also bulk density.

 

[Wil Terry]

ALL loading data for handloaders without pressure testing gear is developed to precise SAAMI pressure limitations for use in the TIGHTEST SAAMI chamber specifications. Nothing else matters !
And so it goes..

 

[orpington]

Longhorn76: It takes a whole lot more than that to offend me!

Any ideas why .32-40 is not in the 49th edition of Lyman's, but a lot less common rounds are???

 

[Slamfire]

Firearms are designed to a load. You can calculate load by multiplying pounds per square inch times the cartridge surface area in square inches. What falls out is pounds.

Rifle chambers carry more load than the receiver as the surface area of the cartridge is greater in the chamber than the portion against the bolt. In revolvers the cylinder carries most of the load. The load path in revolvers is complicated, the frame carries some, the cylinder most.

Prior to 1900, Metallurgy and Mechanical Engineering were very rudimentary. I have no idea how John Brown determined stresses and loads, it is possible, he did not! He might have had "a feeling" on the thickness of structural members. I have no idea of how early firearms were designed. I assume the best designers used ultimate shear load calculations for structural members, but they did not have a concept for fatigue failure. Materials prior to 1900 were horrible. Quality was hit and miss all due to the lack of modern process controls and process technology. If it was not made of wrought iron it was made of plain carbon steels, steels that today are so cheap and low grade that it is used for rebar and rail road ties. Old designs built out of old steels will blow up with loads that the same design could withstand if it was made out of modern alloy steels.

For modern firearms the designer has an excellent idea of the loads and stresses put on the mechanism. The designer examines the loads put on the structural members adds safety factors for the uncertainties that occur in materials, heat treatment, and manufacturing. If the designer adds, lets say, a safety factor of 2, it is not to make the structure twice as strong. Rather, the designer hopes with a safety factor of two, that the device will have a normal lifetime with a load of one. Designers also examine fatigue life. Personnel firearms are considered light duty mechanisms, basically the expected lifetime for a light duty item is around 10,000 load cycles. After that, you can expect fatigue failures. So, if you cut your loads, the mechanism will last longer.

Firearm manufacturers and ammunition manufacturers had to create a level of standardization. No one wants ammunition blowing up firearms, and no designer wants to design a firearm that will blow up. SAAMI is a voluntary organization and gun manufacturer's and ammunition makers more or less follow SAAMI specs on cartridge pressures, sizes, barrel diameters, etc.

Firearms were around a lot longer than SAAMI and there are a lot of firearms out there that were shot much and had little care. The US is awash with old military surplus weapons, many made prior to 1900. Older guns were made out of materials that are inferior to what is available today, and many have already gone through several service lifetimes. European countries require that all firearms pass through a proof house for sales between individuals. I recently read the German proof laws. Prior to 1970, if the firearm in question failed a proof check, lets say the safety was dysfunctional, the Proof House completely destroyed the firearm. After 1970 the law was changed so the Proof House was supposed to only destroy the bad part. I assume that meant your got back your scope, rings, mounts, rifle stock , I don’t know if the Proof House would destroy the barreled action if the safety was bad. Whatever the procedure, the effect of Proof House laws is such that old firearms are weeded out of the European civilian population.

There is no one checking old worn out guns in the US. The owner is assumed to be an expert in these things. However, ammunition companies know that most owners are not very expert in these things, so for ammunition that is commonly used in very old firearms, the pressures are very low. This cuts the lawsuit risk for the ammunition company. SAAMI specs reflect this, pressures for 8 X 57 are about 37,000 psia. Early Mausers, that is the ones made up to 1920 or so, the period service cartridge was around 45,000 psia. That was when the guns were new. Now, a century later, the condition of these relics is very uncertain to an ammunition manufacturer, so 8 mm factory ammunition is not high pressure. In a modern action, made of modern materials (lets say post 1950), you could safely load a 8 mm Mauser up to 30-06 or 270 Win pressure levels, all things being equal, because the materials, processes, and manufacturing are much better.

As to why Lyman has dropped certain cartridges from their manual, you have to ask Lyman. They will probably say something to the effect, hardly anyone shoots those anymore and we have to decide which cartridges to keep, and which to eliminate, or the manual will be so heavy a human won't physically be able to carry the thing!

 

[Jesse Heywood]

Probably dropped due to decreased use. The only ones that know are the editors.

As for a formula, the powder manufacturers have programs that can predict what will occur, but powder burn rates vary, leaving lab testing as the safest method for measuring the pressure curve in the chamber.

You didn't list your bullet weight or type. Some of us have manuals that you might not have.

 

[orpington]

I think it is in the original post...but it is a 170 grain jacketed flat nose.

 

[orionengnr]

There is no one checking old worn out guns in the US. The owner is assumed to be an expert in these things. However, ammunition companies know that most owners are not very expert in these things, so for ammunition that is commonly used in very old firearms, the pressures are very low. This cuts the lawsuit risk for the ammunition company. SAAMI specs reflect this, pressures for 8 X 57 are about 37,000 psia. Early Mausers, that is the ones made up to 1920 or so, the period service cartridge was around 45,000 psia. That was when the guns were new. Now, a century later, the condition of these relics is very uncertain to an ammunition manufacturer, so 8 mm factory ammunition is not high pressure. In a modern action, made of modern materials (lets say post 1950), you could safely load a 8 mm Mauser up to 30-06 or 270 Win pressure levels, all things being equal, because the materials, processes, and manufacturing are much better.

Slamfire validated what I was thinking. .32-40 is an old cartridge, and a lot of guns that fire it are old. How do Lyman and others make allowances for that? By reducing the max load as time goes by.
Makes sense to me.

 

[Malamute]

I'm thinking that the 32-40 is not as common as the 38-55 for certain, and the 40-65 has a following among the black powder cartridge shooters, they likely had enough inquiries to make it worthwhile.

Some guns in certain chamberings may be strong enough for higher powered loads, but they may choose to keep max loads at a level that any gun chambered in that caliber is safe. I believe there have been some single shots of not very robust nature chambered in 32-40.

 

[GLOOB]

In your specific example, maximum load was determined by pressure. Faster powders produce more pressure at lower charge weights.

But maximum pressure is not always the limiting factor. There are plenty of loads that are capped well below max pressure. For instance, cast load data for semiauto handguns is pretty much always capped well below max SAAMI pressure, because those cast bullets don't need as much pressure/powder to get up to speed. Going for maximum SAAMI pressure could cause malfunctions and/or damage to the gun in other ways, due to the increased recoil.

As you said, the load you fired was very mild in recoil (but not necessarily in pressure). Whereas with a cast bullet and a slow powder, it could be possible in some calibers to get a load with massive recoil and still be well under SAAMI max pressure.

Then there are some specific loads that are capped by the maximum volume of a particular powder that the case can hold.

 

[Twiki357]

They also dropped the 32 S&W (Short) from the 49th edition.
And changed the load data for 32 S&W Long. Changed the bullets that data was published for and reduced the max powder charges.
Bullseye for 84 grain bullets:
44th Edition: 1.5 to 3.1 grains
49th Edition: 2.3 to 2.7 grains
I’ve noticed a lot of reduced load data from the 44th to the 49th editions. I assume it’s because of older, weaker guns.

 

[Jesse Heywood]

I read your post 3 times and still missed the bullet. Must be getting old.

From Ken Waters' Pet Loads:
170 Speer FN, Fed 210 primer, 26" bbl.

4895, 28.5 gr, 1,830 fps, Most accurate hunting load in 1894 Win.
4064, 26.0 gr, 1,590 fps, most accurate load with this powder
4064, 27.5 gr, 1,710 fps, Fair hunting load, strong rifle only