Variation in load data

[ZWCoffindaffer]

Does anyone have any insight as to why load data varies so much between different manuals and manufacturers? For instance, I was loading a new batch of 7mm Rem Mag the other night, and I looked into my Hornady manual and into hodgdons website database. What hodgdon listed as a starting load was .5 gns heavier than what Hornady listed as the max for the same bullet, powder, coal, etc. This was the case with multiple powders for that cartridge.

 

[rootie3]

Different guns, barrel lenghts, powders and bullets give different results...

Larry

 

[Reloadron]

Different manufacturers of bullets, powders and components test their load data different ways or more like different test configurations. They publish their results which for as long as there have been loading manuals have differed. Loading manuals provide a guideline for us to work from, they are not cast in stone. Hornady and Speer for example will call out a C.O.A.L. for their bullets which in most cases has an effect on seating depth and the remaining case volume the same holds true for Sierra. Most of the time the published data is within a grain or two but sometimes can vary quite a bit. Bottom line is start low and always work up the loads.

Ron

 

[splattergun]

let's not forget different lawyers. There's always a certain level of concern about corporate liability. Max load data has been drifting lower over the years.

 

[Orcon]

I've noticed something of a trend like that too, powder companies tend to load much hotter than bullet companies. I can only assume this is because the powder game is all about velocity (get 200 fps over other powders by using X-brand powder with new "flimflam" for added power!) and bullet manufacturers focus more on accuracy and/or terminal performance ( the new X-brand hunting bullet with match grade accuracy due to proprietary "flimflam" jacket and "pattycake tip"!)

 

[RussellC]

I notice my Hornady book is more conservative than others like Lee, Lyman, etc.
Hodgdon's and Alliant's info is hotter than Hornady as well, generally speaking.

Russellc

 

[Bart B.]

Even with the same rifle and ammo, several people shooting them off their shoulder from a bench, a 100 fps spread in average velocity can happen. Go figure that out as to why.

 

[Walkalong]

For years I had one watch (Speer manual) and I was happy. Then I branched out, bought a couple more watches, and I was never sure what time it was. I was no longer happy. Then I learned to live with it and used the Speer as my "go to". I was reasonably happy again. Then the powder companies started putting out PDFs on line, and I find them very useful. I still reference the Speer and the Sierra, but I like the online PDFs. I am happy again, but mostly because I stopped worrying so much about the "discrepancies" from source to source.

Pick your source, work up carefully, and be happy.

 

[Jim Watson]

Like Walkalong, although I started with Lyman No 45, my main source was Speer No 9.
I never had a speck of trouble, "pressure signs," or poor accuracy from sporting and military rifles when loading the middle load of the three shown by Speer.

My target rifle loads are slightly below Hodgdon maximums for Varget.

My pistol loads are worked up over a chronograph to one or another specific level, usually to the power factor required for a Division of IDPA or to factory equivalent for defensive weapon practice. Those seldom call for a maximum load.

 

[Dog Soldier]

Splattergun has the correct answer.

 

[Reloadron]

Even with the same rifle and ammo, several people shooting them off their shoulder from a bench, a 100 fps spread in average velocity can happen. Go figure that out as to why.

A little off topic but....

Bart, I tried a science experiment this summer based on that very subject. Here are the results:


The load data was 25gn of AA2495 in .308 Winchester under a Sierra Match King 150gn bullet using LC-10 brass. I loaded and shot 50 rounds 25 each in the lead sled well anchored and 25 off my bags allowing full recoil of the rifle into my shoulder and the rifle was allowed to slide back and hit my shoulder as a stop. The rifle I used was a bolt gun, Remington 700 custom rifle. There was not a heck of a lot of difference between the lead sled and just off the bags. The chronograph used was my old Oehler 35P. The velocities were pretty close with there only being about an 8 FPS delta of mean velocity with the Lead Sled configuration slightly faster.

Ron

 

[Walkalong]

That makes sense. Lead sled was a bit faster.

Also, it tested you against the lead sled. Do ten shooters against it and I imagine you would see more variation with some shooters.

 

[Reloadron]

That makes sense. Lead sled was a bit faster.

Also, it tested you against the lead sled. Do ten shooters against it and I imagine you would see more variation with some shooters.

Absolutely, tried that a few years back. Myself and a friend shooting over the chronograph. Same ammunition with the same rifle but differing numbers. Just about what we would expect. I don't think we got to 100 FPS difference but as I recall we could, with regularity, remain around 50 FPS.

Ron

 

[Sunray]

Lee doesn't count. They use the powder maker's data and test nothing themselves.
Manuals vary because each powder and bullet maker uses different components and test methods. Manuals reflect the atmospheric conditions of the day of the test too.
Barrels are usually on a universal receiver but they can vary in length and rifling twist. For example, Hodgdon's site(that is somewhat wonky by declaring magnum cartridges only using magnum primers when they have nothing whatever to do with the cartridge name. And they mix CUP pressures on the same page as PSI for the same cartridge. There's no converting or comparing the 2.), used a 1 in 9.5', 24" barrel for their 7mm Mag tests. If you have a 26 inch barrel with 1 in 9.25" twist, your velocity will be different. Doesn't mean you cannot use the Hodgdon data though. In any case, a 1/2 grain difference won't make the slightest bit of difference to anything
"...different lawyers..." Doesn't apply. Lawyer loads are an Internet fallacy.