Load Development To Determine A Rifle’s Actual “max” Load.

[Wildfire]

Still waiting.

Hey there:
Still waiting. What did they say????

 

[ants]

The short version, as I understand it.

Here is the condensed version of the engineers' discussion. I would certainly like to hear from engineers or lab techs from other manufacturers to see if they follow the same procedures.

They first determine the constants that will be held, including environmental conditions, type of equipment (copper crusher, strain gauge, or transducer -- yes, they still employ all three), sample size n (typically 20 shots per string), bullet, primer, case type, overall length, chamber dimensions, barrel length, rate of twist, and so forth. Generally, the only variable is the powder charge. From historic data for the subject powder and the constants selected, they determine the range of the independent variable and the delta (how many grains of powder for each string).

They shoot the strings, tabulate the data for each string, and calculate mean and the sample standard deviation for each. Typically the data yield as many as 80 curves. The max load is the curve whose mean plus two standard deviations does not exceed SAAMI maximum. For those of you with a math background, you will understand the importance of "mean plus two standard deviations". In a normal distribution, plus-or-minus two standard deviations from the mean accounts for slightly over 95% of all data, thus only 2.5% of data fall higher than the mean plus two standard deviations.

So why does the table vary from year to year? Because they don't necessarily select the same variables every year, and (as we all know) components change from production run to production run, and thus from year to year. Also, as we all know from shooting across a chronograph, the sample standard deviation depends upon the specific data from that particular string, and can vary from string to string even if you try to hold as many conditions constant as possible.

This also explains why the pressures listed on a load table are usually far below the SAAMI maximum. The pressures listed on the load table are the mean pressures, not the mean plus two standard deviations. Knowing the SAAMI maximum pressure, you can subtract the pressure listed in the table, divide the difference by two, and the result is the population standard deviation for that string. The lowest sample standard deviation will tell you which powders yielded the most consistent results in their tests.

There are no lawyers involved. The lawyers only want to know if industry standards were followed during the lab tests. When industry standards are followed throughout the duration of the procedure, the company is in a very defendable position. Deviations from industry standard weaken one's defense in a claim.

 

[kelbro]

Ants, that agrees exactly with what I have been told.

 

[USSR]

The max load is the curve whose mean plus two standard deviations does not exceed SAAMI maximum. For those of you with a math background, you will understand the importance of "mean plus two standard deviations".

Yep, have had statistics in college, so I am well aware of the bell curve. So, if this is so, then in the case of the .308 Winchester load that I quoted previously, if they are calling 47k psi a "max" load because it was at the peak of the curve and two standard deviations did not take it over 62k, then two standard deviations from that approximates pressures of 32k (on the low end) and 62k (on the high end), with 2.5% going below 32k and 2.5% going above 62k in pressure. Well, certainly a wide bell curve, and quite a swing in pressure. I think them boys better check their reloading procedures.

Here is the condensed version of the engineers' discussion. I would certainly like to hear from engineers or lab techs from other manufacturers to see if they follow the same procedures.

There are no lawyers involved. The lawyers only want to know if industry standards were followed during the lab tests.

So which is it? You can't have it both ways. Care to name the companies involved?

Don

 

[cracked butt]

Max loads are only a guideline. If you believe that maximum loads are never to be exceeded, no harm will be done. Conversely, if you believe that max loads are safe because a reloading company and their lawyers came up with it, you'll eventually be minus a gun and maybe a few fingers and an eye. They are based off the particular rifle the reloading company did their tests on. A rifle owned by you or I is likely to have a different throat, different chamber dimensions, different bore dimensions, different rifling configuration, etc.

This is only anecdotal and not evidence, but I have a Rem 700 in .308 that won't take a 'maxiumum published' load with certain popular powder/bullet combinations for that cartridge without getting a sticky bolt, while I have several mauser 98s that I have fired hundreds of loads over the published 'maximums' without a problem (The load I use is actually a 'maximum load' from an older manual, all of the newer manuals show a maximum powder charge of 2-3 gr less. I shoot this load because its very accurate.) I wouldn't hesistate to work up a load load that went beyond the the maximum load in a new well made rifle. There's a reason for bullet pullers- disassembling cartridges after finding that a lesser load has reached the limits.

 

[.38 Special]

Just a note for folks who are considering trying the OP's method: he's guessing at pressures, and the tools with which he is guiding his guesses are extremely variable. Primers and brass vary considerably in hardness, as do firing pin bushings and ejector holes.

There is a way to push the limits safely, but it requires a blade micrometer wielded by an experienced hand. Better yet is a strain gauge set-up. These two methods are the only way -- outside of a fully instrumented lab -- to safely approach your rifle's limits. Everything else is half-educated experimentation with extremely high stakes.

 

[Zak Smith]

The reality, for better or worse, is that the reloader needs to use a variety of indicators to determine what is too hot of a load for his rifle, with a given recipe. Just as the max might be above "book", it might also be below "book." There is no guarantee that following a book recipe will 100% be under max in any particular rifle.

 

[Bullet]

There is no guarantee that following a book recipe will 100% be under max in any particular rifle.

I’m not saying your wrong but how do the ammo makers (companies) make sure that their ammo will 100% be under max in any particular rifle? Do they download it?

 

[taliv]

There is no guarantee that following a book recipe will 100% be under max in any particular rifle.

this is worth repeating. I have a nice custom rifle that shows pressure signs well below "max".


edit: bullet, they don't. witness all the popped primers with factory ammo in 5.56

 

[Cosmoline]

For every established cartridge, the Sporting Arms and Ammunition Manufacturer's Institute (SAAMI) sets a maximum pressure. The cartridge case and the weapon itself are all capable of handling the maximum pressure without any hazard to safety, and without putting any undue wear and tear on the firearm. No factory ammunition exceeds this maximum, nor does any published handload.

Yes and no. It's actually a lot more complex than that. SAAMI is the US institution that sets standards for US ammunition makers. It does not certify a RIFLE'S maximum load. SAAMI does not inspect the firearms or certify them. Moreover, the pressure maximums set by SAAMI are sometimes at odds with pressure maximums used by foreign makers. If you do much shooting of vintage military arms you figure this out pretty quickly. SAAMI's longstanding max for 8x57js is absurdly low.

And yes the lawyers are involved, or at least liability concerns. The aforementioned 8x57JS is set extremely low for fear some nob with get one chambered in a vintage 1888 Commission Rifle that was never upgraded. This is a questionable fear, considering how few non-upgraded 1888's are even in existence now. And it keeps all US made 8x57JS at a level on par with the .30-30.

 

[USSR]

Just a note for folks who are considering trying the OP's method: he's guessing at pressures, and the tools with which he is guiding his guesses are extremely variable.

.38 Special,

How do you figure I am guessing? I am using a high reputable interior ballistics program which takes into consideration variables such as brass weight and case capacity, bullet, primer, powder, and cartridge OAL. I start well below the SAAMI specified max pressure and I stay below the SAAMI specified max pressure. Look at the data generated by QuickLoad and compare it to what is given to you by your typical reloading manual (Min Load and Max Load). You know, some of the comments here remind me of a typical barrel breakin thread: ie. I don't believe in it and don't do it, so neither should you. Nobody is forcing ANYONE to accept this, but just be aware that there are many experience LR shooters who have been using methods such as I have described for years.

Don

 

[Vern Humphrey]

I start well below the SAAMI specified max pressure and I stay below the SAAMI specified max pressure.

How do you know that? Do you measure pressure? Do you fire enough shots and take enough measurements to be sure that an occasional round won't exceed SAAMI specs?

 

[.38 Special]

How do you figure I am guessing?

Do you know your exact chamber pressure for each experimental shot that you fire? Unless you are using a strain gauge, you do not. And if you don't know, you're guessing.

I am using a high reputable interior ballistics program which takes into consideration variables such as brass weight and case capacity, bullet, primer, powder, and cartridge OAL. I start well below the SAAMI specified max pressure and I stay below the SAAMI specified max pressure. Look at the data generated by QuickLoad and compare it to what is given to you by your typical reloading manual (Min Load and Max Load).

Does it know the exact dimensions of your chamber and barrel? Does it know the strength of your brass and primer? And aside from your extreme faith in your guesses, the only thing brass extruding into your ejector hole is telling you is that you are substantially over SAAMI pressures. Exactly how far over is another guess.

You know, some of the comments here remind me of a typical barrel breakin thread: ie. I don't believe in it and don't do it, so neither should you. Nobody is forcing ANYONE to accept this, but just be aware that there are many experience LR shooters who have been using methods such as I have described for years.

And nobody is forcing anyone not to do it either. We're just providing point and counterpoint for any interested readers. And there are also an awful lot of experienced shooters who have blown up rifles and injured themselves using exactly your sort of load "development". They, of course, thought they were being safe and reasonable as well.

 

[Vern Humphrey]

Like I say, I picture a guy standing on the firing line, the wreckage of his rifle in his hand, eyebrows burned off and face blackened, and saying to himself, "OOOOOkay. The last load would be max if I reduced the charge by one grain."

 

[mkl]

My evil thought reading this thread: Wonder if Quick Load program code for pressure is a regression analysis formula based on all the current load manuals the programmer could find?

My favorite quote from my very first statistics professor: The average human being has one testicle.

 

[USSR]

Do you know your exact chamber pressure for each experimental shot that you fire? Unless you are using a strain gauge, you do not. And if you don't know, you're guessing.

Does it know the exact dimensions of your chamber and barrel? Does it know the strength of your brass and primer?

And Sierra's Reloading manual doesn't know your chamber/barrel dimensions either. Nor does Sierra know the strength of your brass and primer. QuickLoad does take into consideration the weight/case capacity of the brass you are using, something that no reloading manual does. So, your point is without merit.

...the only thing brass extruding into your ejector hole is telling you is that you are substantially over SAAMI pressures.

Hardly. Evidently you have never used Federal or Norma brass.

...there are also an awful lot of experienced shooters who have blown up rifles and injured themselves using exactly your sort of load "development".

Name someone using the EXACT series of steps I have entailed who has blown up his rifle and/or injured himself? Why don't you contact QuickLoad and ask about the validity of their internal ballistics software? Oh, yeah, I forgot, ignorance is bliss. Like I said, LR precision shooters use similar methods all the time; whether you agree with this method or not is irrelevent.

Don

 

[243winxb]

http://www.6mmbr.com/Quickload.html WARNING: QuickLOAD is a computer simulation of centerfire cartridge performance. YOU MUST NEVER just "plug in the numbers" and use QuickLOAD's output for a load recipe. That is foolish and dangerous. There are many reasons why the data QuickLOAD generates may not be safe in YOUR gun. Before loading live ammunition, you should always check with the powder-makers' most recent load data. In fact, you should check multiple sources if possible, and consult with individuals who actually load for that cartridge. Sierra Bullets offers free load maps which, in general, are fairly conservative. Even when using manufacturers' load data, start 10% low and work up. Differences in brass, primer brand, and seating depth can make huge differences in pressure. Always reload conservatively and always double- and triple-check QuickLOAD's output against reliable load data supplied by the powder-makers.QuickLOAD Potential Pitfalls--What to Watch Out For
Even with its impressive level of sophistication, and its amazing store of data, QuickLOAD has a few shortcomings. Some of them are far from obvious and a novice QuickLOAD user might not understand the significance of them.

Temperature--QuickLOAD does have a function to adjust loads for ambient temperatures. However, it essentially treats all powders alike, except for the Hodgdon Extreme powders. As to those, QuickLOAD cautions "Do not use with Hodgdon Extreme Powders". Well any seasoned reloader knows that all powders don't react the same to swings in temperature. And we can tell you that even the Hodgdon Extreme powders deliver more pressure in very hot summer conditions, compared to cold winter days.

Primers--QuickLOAD lets you adjust for a myriad of cartridge variables, such as groove diameter, case volume, and starting pressures. It can even adjust for moly bullet coatings and bullet shape (flat-base vs. boat-tail). However, there is no simple means to compensate for different brands of primers. Reloaders should keep this in mind when working up to "max" load levels. Hotter primers will affect the powder burn and can raise pressures.

The Mysterious Weighting Factor--QuickLOAD has a "weighting factor" it uses to help tailor output values to cartridges of various different shapes and sizes. The default for bottleneck cases is 0.5. "Overbore cases" have been assigned a value of 0.33. But if you click on the 6mm Dasher cartridge profile, the weighting factor is 0.4. Presumably that represents some kind of judgment call, but QuickLOAD doesn't really provide any criteria for assigning a weighting factor to a particular cartridge that is not a "typical bottleneck." For what it's worth, the default value for the 6BR is 0.5, but we got better results using a value of 0.45.

The Need to Check Data Entries and Tweak Some Variables--QuickLOAD has tens of thousands of numerical values stored in its bullet and cartridge databases. As you might expect, there are a few errors. That's why it's very important to double-check data entries against your own measurements. But the process of inputting your own corrected data actually unlocks some of the program's real potential. As Firehawk observes: "The true power in QL lies in its potential for calibration. This is a huge advancement in reloading. You measure your bullets, your fired cases, velocities from YOUR barrel. Then you make the appropriate adjustments in QL to match. At that point, with those components, QL is very accurate. More so than any other reloading system ever before it. After a few years of use, developing a routine and building a base of adjusted components, QL's second biggest virtue comes into play--it can run 'What Ifs'. This is very cool. I can run from cartridge to cartridge with nearly any powder or bullet, and instantly see the best potential for my rifles or future rifles. Nothing's perfect though, and there are things in reloading which are difficult to quantify. Starting pressure, weighting factor, friction proofing, powder temp, even bore volume. There are default values preloaded in QL for these, and they are normally wrong. Same with the default seating depths, bullet dimensions, powder specs, and case volumes. QL, out of the box is just a starting place. Make it part of your routine to correct these, else you forget or miss something."

 

[steve4102]

I have talked many times with different folks in the ballistics bussines.
Reading brass is not a very good way of developing loads any more

What has Sierra told you about their manuals and how they determine a Max load?

I called them a few weeks ago and asked why they did not list pressures in their manuals. I was told that they do not list pressures because they do NOT have pressure testing equipment. They do it the same way you and I do, read the brass and use a Chrony. Interesting that a bullet Co like Sierra relies on these old techniques ain't it.

 

[.38 Special]

Well, Don, oddly enough you are not the first pressure guesser I have ever talked with that got hot under the collar when someone pointed out that looking at damaged brass isn't a good substitute for getting a doctorate in the field and then spending thirty years in a fully instrumented lab.

And when the pressure guessers start with the insults, I find something else to do. So have a nice day.

As for any innocent readers left on this thread, I again leave you with the message that while lots of folks have gotten away with pulling this particular tiger by the tail, lots of others haven't. When you decide you know more about it than the white coats at the lab, you are betting your rifle and your body parts on it. For my money, if you can't get your bullet to go fast enough for your purposes, you need a bigger gun.

Have fun!

 

[USSR]

Well, Don, oddly enough you are not the first pressure guesser I have ever talked with that got hot under the collar...

LOL, "hot under the collar"? I would say you were closer to that, trying to rebute a fairly common practice that you are obviously totally unaware of. Perhaps if you went to some other sites frequented by LR shooters such as http://www.snipershide.com you would learn something about load development. In closing, I wish you a nice day as well.

Don

 

[.38 Special]

FWIW, what I know about load development was learned in the benchrest game. I won't claim those gentlemen know every last thing about the subject, but they're not exactly ignorant of it either.

Doubtless the amateur snipers know more about it than the people setting the records. Not to mention the people with the degrees and the fully equipped labs.

 

[243winxb]

USSR, what are your thought on measuring the web to check for high pressure? http://www.thehighroad.org/showthread.php?t=372913 From Speer> Quote:
"When the pressure for a load causes the head of the case to increase in diameter measurably, then the load is excessive for the case being used. An increase in head diameter of .001" would MORE THAN indicate excessive pressure"
My thought on it>
"Note, this is a bottle neck type case like 30-06 or 243win. mkl Looking at my Speer manual #8 your above quote is correct, but i think the measurement is taken on the web just in front of the extractor groove. The web is part of the head as shown on page 27. The rim gets more abuse as its in contact with the bolt face and i feel not the correct place to measure,if your going to use that method at all."

 

[243winxb]

First, I will state that this is how I approach it, and it should only be done by experienced reloaders with the knowledge and equipment to do so safely. While this has worked well for me for a number of years, I accept no responsibility or liability for your load development.

Well, there are two types of Max loads. First, there are published Max loads, which are in fact not actual Max loads and vary according to the publisher's lawyers. And then there is the actual Max load for your particular rifle. If you are not an experienced reloader, then you should stay within the publisher's Max load data. However, if you are a reloader with the knowledge and suitable equipment to determine your rifle's Max load, then here is how I approach it with a modern bolt action rifle. First, you should have a chronograph, and have an idea as to what reasonable velocity you can expect from your platform (ie. boltgun vs. autoloader, barrel length, etc.) with a particular load. Second, you should be able to look at brass and see high pressure signs. The brass is the weak link in firing ammunition in any rifle, and will show signs of stress LONG before there is any danger to the structural integrity of the rifle itself. Always start out with a load well below the published Max load. You may not always be using the same brass or primer as was used in the reloading manual, so take that into consideration as well. I like to load 3 cartridges with a particular charge weight of powder, and then load several series of 3 cartridges with a slightly heavier charge weight, varying the charge weight of each series of 3 cartridges by 0.3 grains. At the range, you will start with the lightest charge weight cartridges and run them across the chronograph. Here is where you need to have an idea as to what maximum velocity is reasonable, and what is not. In a bolt action .308 Winchester with a 26" barrel, a 175gr or 178gr bullet can usually safely attain 2750fps with a suitable powder. If you reach that velocity without pressure signs, then don't push it. Now, what are the pressure signs. The first sign of pressure (both low and high) is transfered to the primer. With low and normal pressure, there will still be some "roundness" to the edge of the primer. Once you decide to run at a slightly higher pressure (but still within the SAAMI pressure specs), you will see flattened primers. While flattened primers are generally a sign of high pressure, they do not by themselves indicate that you are anywhere near the maximum pressure specified by SAAMI. Another sign commonly associated with high pressure is cratering of the primer around the firing pin indentation, although this can also be the result of an enlarged firing pin hole in the boltface. Basically, what I am saying here is, while you should take these signs into consideration, primers can and will lie to you. So, as you continue with the next series of cartridges (assuming you have no other signs and have not met the afore mentioned predetermined optimal velocity figure), the next two signs are what bring you to your particular rifle’s Max load, and cause you to stop further load development. Oh, and make sure you have a bullet puller, because you will have no doubt loaded a series of cartridges beyond this point. What will happen next is usually you will see a shiny mark on the headstamp of the brass. What this is is the brass is beginning to flow into the extractor hole in the boltface, and it gets shaved off as you turn the bolt to extract the case. If you see this, or if the bolt becomes hard to open to extract the case, then you have reached your particular rifle’s Max load and shooting should stop and all subsequent loads should be pulled. Any subsequent reloading using the same components should have a charge weight of at least 0.5gr – 1.0gr less than the load that showed high pressure signs. Using the above method, I have been able to obtain optimal performance for LR shooting, assuming I find an accuracy node in this pressure range. YMMV.

USSR, i agree with some of your first post, the method used to work up a load is good. But i feel data published for rifles is correct as to maximum loads using IMR Powders. The key factor in pressure difference is the make and type of bullet as i see it. I would love to see your load data. How does your load compare to published load data? What bullet,powder, calilber, primer,case, action, custom chamber or factory, barrels are you using. No wildcats please.

 

[243winxb]

Case head separation. Shiny ring around the head

Sigh of high pressure or case wear? After about 3 firing was a maximun load the shiny ring appears. This is with factory rifles and FLRS standard dies. I feel its from one of 2 causes. 1.The brass has come to the end of its usefull life because of high pressure. 2. Or the FLRS dies is not adjusted correctly, the loaded round has had its shoulder pushed back to far, leaving excess head spacing. This ring does not seem to appear as fast with light loads.

 

[USSR]

USSR, what are your thought on measuring the web to check for high pressure?

243winxb,

While I don't personally use this method, it is a method used by many, in particular many old time reloaders. What is important, IMHO, is that you use several methods in conjunction (published data and/or internal ballistic data, chronograph data, knowledge base data, previous experience, and whatever method you use to note the postfiring condition of the brass.

The key factor in pressure difference is the make and type of bullet as i see it.

You would think so, but actually, the brass and primer used have a much more profound effect on pressure than does a switch of bullet make (assuming both are of the same weight and configuration). Somewhere I've got a scan of data compiled by The American Rifleman technical staff showing pressure readings when the following is changed: brass make, bullet make, and primer make. There was little change when switching between makes of 168gr HPBT bullets.

Sigh of high pressure or case wear? After about 3 firing was a maximun load the shiny ring appears. This is with factory rifles and FLRS standard dies. I feel its from one of 2 causes. 1.The brass has come to the end of its usefull life because of high pressure. 2. Or the FLRS dies is not adjusted correctly, the loaded round has had its shoulder pushed back to far, leaving excess head spacing. This ring does not seem to appear as fast with light loads.

If you are talking about a shiny ring around the web portion of your brass, then it is indeed #2, an incorrectly adjusted FL die causing the shoulder to be pushed back too far. High pressure only aggravates the condition, which is why it doesn't appear as fast with light loads. The RCBS Precision Mic is a very handy tool, and I use it with all my cartridges so as to set up my sizing dies properly. All the above is simply my opinion based on my experience, and YMMV.

Don