why a difference in load data between manuals

[pinfish]

Hi all, I started loading the 308 win. with 150 grn. hornady bullets and varget powder. The hornady manual lists starting grns. at 35.9 and max at 44.9. the second edition Lee manual lists starting grns. at 44.0 and the max at 47.0. The data for my .243 loads are almost identical from one manual to the other. Any comments on the 308 data would be appreciated.

[t45]

Not much help here but I have noticed my Lee manual (10rs old) indicates some higher charge weights compared to the rest of my manuals of the same years. I have not bought a recent addition to compare. Good luck in your quest.

[TXGunNut]

Welcome to the asylum!
Lyman lists 42.5 min, 47.0 max using a Hornady bullet. Lower velocities and pressure than Lee listed as well. Lyman used a universal receiver, Hornady a Model 70. Speer lists #'s close to Lyman and Lee, used a M700 for testing. Hodgdon #'s very close to Lee's but pressure is in c.u.p. That's why I keep more than one manual around.
Start low, work up. I suspect you'll find a good load before you get to 47 grains, maybe even before you get to 44.9.

[4runnerman]

Difference is simple and mostly true,,, DIFFERENT LAWERS. Most loads if not all in books are low to say. The companys that do the loads do not want to be guilty of you blowing yourself or the gun up in your face,so they make their max loads safe under most conditions for all guns. They do put in warnings to never exceed max loads as another way of clearing themselfs of any liability that would or could happen if your load more than they say. They have to take into account old and new guns and be safe for both.

[NWPilgrim]

The various testers used different firearms, with different chamber dimensions, different case headstamps, different primers, maybe different temperatures, and overall lengths (bullet seating depth), etc. Starting loads can definitely change a lot because it is somewhat arbitrary, usually about 8%- 10%.

That is why you start low and work up to max for your rifle and components.

[geetarman]

Some manuals will have two sets of load data for rifles. One for semi auto and one for bolt guns. My Sierra manual in particular shows different loads for .223 and .308 depending on intended use. I expect you will see something similar for 30.06 intended for bolt guns and for M1s.

Geetarman

[Shoney]

Each manual lists the weapons and components they use, but don't give you all the info. Combinations of these and other factors can cause great variances in velocity and pressure. Chasing these variables to get to top accuracy can drive a sane person nuts.

Below is a listing of a few factors I have come across {and NO I am not going to explain them, Other folks have published articles and books on the subjects} in loading manuals that can add to differences in loads.

Primer: strength, brisance - is a measure of the rapidity with which an explosive develops its maximum pressure
Barrel: length; tightness of bore; height of the lands; distance of bullet to lands; temperature of barrel;
Lock Strength: the force which is applied to the primer by various strength firing mechanisms;
Bullet: bearing surface of bullet, alloy of bullet; shape of bullet; distance off rifling;
Brass: new/used elasticity; manufacturer, volume; crimp;
Powder: new, aged, old, batch powder was from;
Weather: ambient air temp., barometric pressure, humidity
Elevation: above sea level
Other: I am sure I have not listed all

[WESHOOT2]

Manuals are guides.

[pinfish]

thank you all for your replies and experience. I shall be a happy and more informed loader now.

[WESHOOT2]

Fact: There are no lawyers sitting at the reloading bench. Improved measurement methods are why data is "watered down".
For safety.

[full case load]

I used to wonder too, and often if I wanted a hotter load I'd go back to one of my old manuals. I've been looking for data on a Blue Dot load that is not published and in that quest have been told the older manuals used the crushed copper (cup) units of measurement. Newer data has come out since the use of Peizo conductors to get direct pressure measurements and the use of strain gauges has yielded more complete actual pressures throughout the burn. (Disclaimer; since I'm not a scientist and probably not even as smart as I think I am, some of that may be slightly out of context or even wrong in that I misunderstood some of what was being explained to me. However, it makes sense to me and I'm not going to the older manuals to find a hotter load anymore.)

[Clark]

The 308 uses the 1889 7.65x53mm Mauser case head built with large Boxer primer pocket.

In 1905 the 8x57 was sending a 150 gr at 2900 fps, which we know today takes that the same case, but with Berdan primer, to about the same pressure that limits the case head with the Boxer primer.

This case head is good for 65k ~ 70kpsi before short brass life in handloads for an individual rifle.

The 270 and other cartridges using this case head were registered at SAAMI as 65kpsi average peak pressure many years ago.

We would have thought that the 308 would have been registered at 65kpsi, but it was registered at 62kpsi.

More recently, the 260 with this case head was registered at 62kpsi, maybe because there are manufacturing variations and different rifle variations for factory ammo in unknown rifles.

The SAAMI registration and loads should be designed to stay a safety margin away from the weak link in the system, the large Boxer primer pocket.

But that is reality and pressure measurements and published data has taken on a life of it's own.

Often in engineering there is a polarization of two political parties; "follow procedures" and "get'r done".

This polarization in reloading strong rifles, like the 308 would then divide us into two parties, one trying to find the one true load book to follow with load book fundamentalism, and the other camp finding the threshold of short brass life and backing off a safety margin.

[wncchester]

"The data for my .243 loads are almost identical from one manual to the other. Any comments on the 308 data would be appreciated."

It's no big thing, what you are seeing is the normal variations between rifles. Their .243s were similar. Their .308s were not. Your's isn't like either of theirs, THAT'S why the books all say to start low and only work up to book max unless you run into pressure signs earlier.

The only thing the "lawyers" put into the mix is to tell the ballistics engineers to be sure their published charges don't exceed SAMMI specs for the cartidge. That doesn't sound unreasonable to me. Anyone wanting to go passed book max loads has the privilige of doing so without having to ask the publisher for permission, no matter what the dumb ballisticians and silly lawyers say. Who knows, it may even improve the gene pool! ??

[Loader9]

Wanna really get confused, go to Accurates website and look at their pdf reloading data for a 357 magnum. Now do a search(easiest way if you don't have it bookmarked) for Accurate data on the 357 Magnum in CUPs. The pdf is in PSI and the other data in CUPs you would think would be fairly close- it's not. For a Speer 140gr JHP and #5 powder, there is almost a full grain of powder difference. Other powders also show a significant difference. As most know, the 357 Mag was designed to shoot at 47,500 CUPs but the inferior guns of the day (read Smith and Wesson) couldn't stand up to the beating. The pressures have been lowered several times for this reason and the 357 Mag is just a hot 38 Special now....if you use the new data and have a newer pistol. Pressures are now 35,000 PSI.

[Gregory Gauvin]

Also take into consideration the differences in barometric pressure (altitude) of the testing sites for various discrepancies in load data.

[SL1]

is SUPPOSED to be taken in a SAAMI spec test barrel. Those barrels are made to much tighter specifications than factory guns, with minimum specs where they will create the most pressure. When these barrels wear beyond certain values, they are supposed to be retired. This is the barrel that sets the CHARGE weights, and one would think that there SHOLD be minimal differences in the results from lab-to-lab, since that was the INTENT of the testing protocol.

The VELOCTIY measurements are a DIFFERENT story. Because the SAAMI-spec'ed test barrels tend to produce higher pressures AND VELOCITIES than the commercially available guns, the manual publishers typically ALSO test their published loads in a typical gun chambered for the cartridge to give the relaoder a more REALISTIC idea of what velocities he is likely to achieve with the published loads.

So, the pressure is actually from one gun and the velocity is usually from a different gun. Shooting the same loads in several commercially available guns will demonstrate that there is a LARGE variation in velocities from them. THAT is a large part of the explaination of the velocity differences for similar loads from manual-to-manual. BUT, it doesn't have a thing to do with the CHARGE WEIGHT differences, which are SUPPOSED to be coming from as nearly identical tests as possible.

There are a lot of differences in things like powder lot variations, primer brands, case capacties, bullet designs, etc. that DO affect the pressure tests differently in different manuals. More than a 10% variation is unlikely from those factors, so that is why most start charges are reduced 10% below the max loads.

But, SAAMI has also changed the pressure standards and even the measurement protocols several times. Some of those changes are due to "new information" that comes from being able to observe the whole pressure curve (PSI) instead of just the effects of the peak on a copper cylinder (CUP). Especially in revolvers, it was found that the pressure curve looks much different than in a test barrel chambered for the same cartridge. And, in rifles, secondary pressure peaks sometimes appear when power burning rates are not really suitable for the cartridge. So, loading data has been adjusted to reflect such new knowledge.

BUT, new knowledge does NOT explain all the changes that SAAMI has made in pressure standards. The .357 and .44 Magnum cartridges have CLEARLY been down-rated in the transition from CUP to PSI. "Reasons" given by the various gurus don't really stand-up to factual discussion. It has gotten so bad that it is obvious that SAAMI should have adopted a "+P" designation for those cartridges in the PSI standard that is similar to the old CUP standard. But, they have consistently failed to do that, although they have allowed the old CUP measurement process and standard to continue in use. That is why we consistently see new data for these cartridges in CUP in some new manuals.

SAAMI is an INDUSTRY group, not a government regulator, so the standards they produce have some influence from commercial considerastions as well as safety. I suspect that there is a large push to make newer cartridges seem more desirable than the old ones, so that we will rush out and buy new guns, loading tools, etc, and make them bigger profits. Some of the new revolver cartridges were standardized at pressure levels that are just too high for long brass and even gun life. So, why not let the old cartidges CONTINUE to have the same "luxury" of loads that are going to beat-up guns and brass if used continuously? Especially now that SAAMI has the "+P" designations in the new PSI standard?

SL1

[mehavey]

I suspect that there is a large push to make newer cartridges seem more desirable than the old ones, so that we will rush out and buy new guns, loading tools, etc, and make them bigger profits.

Ooooooh.... CONSPIRACY !
Gotta Luv it don'cha know.

[wncchester]

Sheessh!

[Gregory Gauvin]

In summary, buy a chronograph. Check your brass.