Why The Inconsistency?

[Wiskey_33]

Why would one manual recommend one charge as max, and another manual have something quite lower for the same bullet as their max?

I'm talking IMR 800X and 180 gr. XTP's. Hornady manual says 10.1 for MAX, but I've read that some think it's too hot. Their 7th shows 10.1, and their 4th shows 8.8

What gives?

[Wiskey_33]

Anyone?

[greco]

Make sure you are looking at the same powders. At one time they used to list powders with the same number such as 4064 and 4064 IMR with different loads because different lot numbers burned at different rates. Also, I noticed older manuals have hotter loads because the newer publishers are more prone to CYA.

[woods]

Because they redid the pressure testing and came out with a different result. Or they got a memo from their legal department that said to reduce liability they needed to be more conservative.

The problem with all these manuals is that each manufacturer does testing on it's own and there are no standards for equipment and procedures. That's why you should use the manual data as a guideline only and start lower and work up to max in your gun. I have seen examples of manual data being too high and a particular gun reaching max load before the manual load but most of the time the manuals are conservative.

[WESHOOT2]

Manuals are guides ONLY, as EVERYTHING they use is different from EVERYTHING you use.
My gun, my component lots, my tooling, my test environment and equipment, are DIFFERENT from any other.

This is specifically why all manuals mandate that one start low and work up slow.

[SL1]

I think that the "Everything is different" theory only gets you so far.

There are a few examples of loads in published manuals that just look substantially different from what others have published for the same powder and similar bullets. There are a lot of possibilities as to how that COULD have come about, but there are usually no actual explanations of how one DID come about. So, we are left to speculate. And there is a LOT of speculation on the Internet, some of which is way off base, and some of which MIGHT be right.

The only thing that one can do is to obtain multiple sources of pressure-tested data and try to develop an expectation of what a particular powder can do with a praticular type of bullet in a particular cartridge. Then, when something looks odd, at least you know that from the beginning. So, you can either choose to avoid the potential problem by not using that powder in that application, or to be extra careful as you work-up a load.

SL1

[uncyboo]

When looking for new load info, I try to find as many reputable sources as I can, and take and average of all the start loads, and all the max loads, and go from there. It tells me where to start, and where I should probably end up. Or close to it, depending on what my rifle indicates.

IOW, pretty much whar SL1 said.

[Unclenick]

Its partly history and partly historical artifact. Woods is incorrect about there being no standards for procedures or equipment—that is what SAAMI exists for—but he is correct in the sense that many manual authors don't comply with them. They are expensive to adhere to.

When SAAMI publishes a cartridge specification, it includes three drawings: the cartridge, the chamber, and the test barrel. The test barrel has tighter tolerances specified than the chamber drawing, so the test barrel winds up with a minimum size chamber and a bore that is not oversize to the limits allowed for commercial bores. This creates the highest (worst case) pressure condition at any given ambient temperature. A loose chamber and bore sees lower pressure with an identical load. Typically, if you see pressure test data, the load was fired in a test barrel, and because that constitutes a worst case, it should be safer than a load worked up in a commercial firearm, as many manuals use. That assumes the test barrel was not shot out and is in good condition.

In addition to the above, many shooters have been misled to believe all cases for the same chambering, all bullets of the same weight, and all powder and primer lots of the same names, are interchangeable. They are not. In particular, watch the Cartridge Overall Length (COL) numbers, as different seating depths change pressures. Some powders vary with lot number more than others. In the case of the OP in particular, I use the QuickLOAD internal ballistics software a lot, but its powder database does not include 800X or any of the other IMR pistol powders. I asked the software's author why, and he responded that they have changed suppliers for those powders so many times over the years, he does not consider them consistent enough to safely include in the database. The IMR rifle powders, on the other hand, have come out of the same Canadian plant for a long time and are very consistent.

Many old manuals that have pressure test data and military manuals up into the 1990's report copper crusher numbers as "p.s.i." Copper crushers proved non-linear and erratic if the same loads were sent to several labs. Their output is also sluggish (pun intended) and reports an average working up to the peak. When piezo transducers began to replace copper crushers a number of anomalies became apparent that the copper crushers, even on their best day, don't reveal. See my post #35 in the Blue Dot warning thread. Similar unexpected pressure spikes in loads long thought to be fine from copper crusher testing turned out to behave unexpectedly when all the details became visible, producing odd spikes that were not explained and were therefore backed off. So it's not all about lawyers or fear of aging guns in circulation that might fail. Some of it is technical.

Again to the OP, a good rule of thumb that has developed over time is to find at least three different sources of load data for any chambering/bullet type/powder combination, and use the smallest starting charge listed among the three.

[Bart B.]

Woods mentions:

The problem with all these manuals is that each manufacturer does testing on it's own and there are no standards for equipment and procedures.

I agree that most folks developing loads to publish anywhere does their testing on their own.

But there is a standard although few of us abide by it. SAAMI established pressure and velocity testing standards for most commercially made ammo some time ago. There are specs for pressure test barrels' chamber and bore dimensions that are more stringent than those for standard barrels. Specific pressure testing tools and procedures are also established. There's even an exact prescribed method to remove a round of test ammo from its box, turn and twist the round just so and chamber it; all the exact same way so shifing powder in the case doesn't give different pressure and velocity numbers. And some ammo companies make special test ammo loaded to exact SAAMI standards for normal, maximum average pressure (not proof test loads which produce higher pressures) for special applications.

The following link used to get a ".pdf" file opened up one could download and save:

http://www.saami.org/Publications/205.pdf

I just tried it and the document no longer shows up. Maybe SAAMI decided to no longer make this available to the general public.

It's easy for 10 different people using the same make and type of case, powder and charge weight, primer and bullet to get a 150 fps or more muzzle velocity spread among them. Their barrel, chamber and test procedures used are the biggest variables.

[oneounceload]

Some companies differ due to equipment used - some will use a pressure test barrel, others will use an actual firearm, yet others may use a firearm, but with a different barrel length - make sure you are not only comparing apples to apples, but the same kind of apples to each other.

Ammunition makers use proprietary blendings you cannot get or duplicate to achieve a "norm", bullet makers tend to use what you can get off the shelf - but then again, as has been said, testing conditions and environments differ greatly.

If you haven't started out at the lowest and worked your way towards max, you should.

[WESHOOT2]

Take a specific lot of ammo and chronograph it from ten guns (or more) of the exact same model.
Then determine how you could possibly get such a wide velocity variation.

Then try the same experiment with the same load but different lot.
Or change one component lot.
Or test in ten more guns.
Or on a different day.
Or with a different chronograph.
Or in a different location.

My my my........

[GP100man]

Whiskey

800x is a hard powder to handle & not very popular , but I like it!!!!

& use it !! in 44 mag I use it under a 200gr. XTP with very good results & in 357 mag with the 358429 bullet (173gr. SWC) with good succes with the alloys I have on hand!

I chronographed my loadings that I loaded "by the manual" & backed off a bit ,from my calculations & thats a gray area of gray matter!! I was nearin 46,000 psi with a jacketed load & the new"SAAMI " limit for the 357 is 35,000psi so I`d rather ere on the lower side so to say!!!

I still manage to stay in or near 1300 fps with the lower loadings though.

this brings up SAAMI limits , we`all know they lower the limits for a CYA type thing , but take in consideration the droppin limits , some in PSI , some in CUP , different bullet designs ,we won`t mention the different test platforms, the powder manufactures tolerances , they do a good job of offerin a guide to START with & It`s up to us to ultimately to look out for ourselves.

[SL1]

Yes, there are a lot of differences that affect the VELOCITIES given in manuals. Those are usually the velocities that were produced in a commonly available firearm for that cartridge, NOT the velocities from the test barrel that was used to get the pressures and establish the max charge. The reason that is done is to give reloaders a realistic expectation for the velocities they can really achieve. Test barrels are tighter than most commercial guns, and often are not the same length as barrels on commercial firearms, and rarely contain gaps that are truly representative of the cylinder-to-barrel gaps in commercial revolvers.

BUT, the PRESSURES in modern data provided by the major powder and bullet manufacturers SHOULD be much more consistent, because those come from the laboratory pressure-test barrels. There are much tighter specs for the pressure-test barrels and some pretty good procedures for calibrating and using them. And, current electronic measurement systems are much more easily calibrated than the old copper crusher system. So, the question about why maximum loads differ from manual to manual is a MUCH different question than why the velocities differ.

SOME of the differences in max loads are certainly due to things like variations in powder lots, different choices for primers, and different case capacities, none of which are published with the data. (If that information, plus the velocities from the test barrel, were ADDED to what is currently published, it would help a LOT in figuring-out what is really causing any noted inconsistencies). And, of course, there sometimes are differences in COL, and then there are obviously differences in bullets that affect powder space and pressure even when they are loaded to the same COL. (It would be nice if the manuals would list the actual lengths of each bullet - - which would be a lot more useful than the sectional density that many spend the space to list.)

So, it is usually possible to look at modern max load data and SPECULATE that the inconsistencies are due to things that we don't have information about. But, sometimes, we see that other data for the same powder is more consistent than a particular piece of data that seems inconsistent enough to matter. That tends to make the speculations about powder lots and other unknown variables a little less likely to be the actual cause.

And, there are always speculations that some data were not produced with the proper equipment or procedures. Some of that may be idle speculation from people not in-the-know or even with axes to grind. But, there are reasons to believe that errors happen, because manual publishers have sometimes gone back and retested particular powder/cartridge combinations and changed ONLY those loads, without changing all other loads using the same powder. They obviously know things about their own data production that they aren't telling us.

I hope I live (and reload) long enough to see manual publishers TRY to include the addtional data that would help us more fully utilize our new tools like QuickLOAD. But, it is a matter of production costs of the manuals as well as the data. More information takes more space and can mean more pages, as well as more proof reading. So, if it happens, expect it to cost more. But, I know that I would be willing to pay for it.

SL1

[freakshow10mm]

Powder formulations change and aren't noted as well. Sometimes a distributor will use a specific lot for a few years then when consistency suffers they switch to a different lot of the same powder, retest, and the results will vary from the old lot. Sometimes the max load of what we think is the max pressure isn't, but is the max charge that gave the lab acceptable performance they thought handloaders would use. This same variation differs with the powder company versus bullet manufacturer testing the same components.

As has been said previously, a large portion of the handloading community thinks the manuals are the gospel and don't use them like they should. It's a guide and merely a guide. The only way to know for sure is to work up loads in your gun under your environment and interpret the results yourself. Loads worked up in Montana at Western Powder will not produce the same results as loads worked up here in the Upper Peninsula.

The more experience you get as a handloader you will understand more and more what's going on and more importantly why. You will develop techniques that are advanced for even seasoned handloaders.

[Unclenick]

Pressure is messy. If you have a load at high enough pressure to stick the case to the chamber, the peak pressure you will reach has a direct dependency on the volume behind the bullet that the inside of the case expands to inside the chamber. That varies with the brass volume and the chamber dimensions and how deeply the bullet is seated into the case. For loads not high enough in pressure to stick brass, peak pressure works out to be closer to dependent on the sized case volume rather than that it expands to. This has to do with how fast the powder builds pressure, but the dividing line tends to occur with loads that are in the vicinity of 30,000 psi peak pressure, give or take 5,000 psi or so. Below that rough line you have sized-case volume pressure dependency, and above it you have fireformed case capacity pressure dependency.

If you look at the SAAMI drawing for the a .308 Winchester, the pressure test barrel is specified to be 24", which is a common SAAMI test barrel length for medium power cartridges. When you look up the claimed velocity for commercial .308 ammunition, that's the barrel length it was taken at. Makers often don't offer that in their specifications. The chamber is indeed at SAAMI minimum dimensions, as I described in my first post, because that makes for maximum pressure from the load for these more-than-30,000 psi rounds.

When a cartridge is given SAAMI recognition, it becomes the responsibility of the company who originated the commercial round to supply proof and reference loads to the industry for it. Cartridges whose original developers are out of business or which were military developments are assigned to SAAMI member ammunition manufacturers. If you are, say, Federal, and are making .308 Winchester loads, you fire ten reference rounds supplied by Winchester in your pressure test rig, and whatever average reading that gives you on your equipment is supposed to calibrate your gear to match the SAAMI standard as measured by the responsible manufacturer's equipment. Whether the absolute accuracy in psi is true is not isn't the issue; learning what the peak reading value on your equipment with the reference loads is. This is intended to offset small dimensional differences in your test equipment from the responsible manufacturer's or in the conditions you fire them in. The new Federal load's average peak reading cannot exceed that found on their own equipment using the reference loads.

Some thought will reveal there are potential problems with the reference load approach. For example, Federal might be using a powder with different sensitivity to temperature change than the one in the Winchester reference loads. That would mean the peak pressure limit they find in their tests are only validated by the reference loads from Winchester at one temperature. A bigger problem, in my view, is sample size. Commercial ammo occasionally gets recalled for being too warm (nobody recalls ammo that's too wimpy). I think that's traceable to the fact 10 is not a statistically significant sample size. Random Gaussian events need a sample size of at least 30 to begin to have reasonable confidence the average result is at the center of the bell curve for future copies of the same load. Same for firing reference rounds to know you've got a good average peak value as measured on your test equipment. (The military insists on bigger samples—something in the 80's, IIRC—for anything that is destroyed or consumed in testing.)

I discussed that sample size issue with SAAMI technical director Ken Green a couple years ago, and he indicated the industry just didn't want to spend the time it takes to fire samples that large. That doesn't make 10 round samples adequate. Just better than nothing.

Meanwhile, if your chamber is bigger than the test chamber used in a manual, you will get lower pressure and velocity, assuming all else is the same? Often it isn't. Older guns often have different throat and freebore dimensions. Brass weight and internal dimensions get changed over time. So, even if the bullet, primer, and powder are identical, you can't really count on exactly duplicating any published load's pressure or performance.

[freakshow10mm]

And some manufacturers test along the barrel a few inches forward of the chamber, which will yield different results and sometimes they will offer a max load with lower chamber pressure due to the pressure build. You might have SAAMI compliant chamber pressure but 6 inches down the rifle barrel it will spike over SAAMI. The chamber pressure is in spec but the barrel pressure exceeds it. The manufacturers will drop the data to a safe level so that chamber and barrel pressures are kept below the SAAMI spec.

As an aside, this is what makes the Hornady Light Magnum ammunition what it is. They play with this timing in the pressure build so that the peak pressure isn't in the chamber it's in the barrel once the bullet leaves the case neck. Sort of like a two stage rocket. First stage gets it off the ground and once suspended in flight a boost puts it to terminal velocity. Use a double base powder with 3-4% more nitroglycerin than others coupled with surface deterrents that slow the initial burn to allow pressure to build, delay complete burn, and shift the pressure curve ahead without making it increase. Chamber pressure and barrel pressure remain safe but the velocity increases. Same technology Norma uses to load Federal's Hi-Energy loads.

It's stuff like this why I love handloading so much. The minute details all culminate and occur within a few milliseconds to give us an amazing result in performance that we can manipulate to a certain degree by changing one parameter a tenth or a thousandth of something.