Double-check relaod soruces

[DCmauser]

For light Sunday night reading I was browsing thru my copy of the The Complete Reloading Manual Load Book for the .45-70 gov't.  [It is lighter than the Lee Precision Modern Reloading book].  I was thinking of copying select data, say for IMR 3031, into some MS Excel speadsheet to create a fancy chart, see trends, extrapolate or fill the gaps between data from bullet and powder manufacturers.
 
The first page started with Hornady, 350 grain, with same cartridge, primer, barrel length and twist, and wondered why 3+/-grains difference to get to the 1700, 1800 & 1900 fps velocities, between Marlin and Ruger actions?  Maybe its because of the 'spring' in the lever action bolt as Col. Townsend wrote about - but 3 grains or 6%, that seems like quite alot! 
 
I figured okay then just stay away from those Ruger loads.  Then I noticed that even for the Marlin loads, for 3 powders only, (RL-7, 4198, 3031), that the book listed more powder for the lighter 300-grain than for the 350.  Not good, I think.
 
Maybe a simple swap of some data, rows columns are so confusing, but maybe some other error.

[Dinny]

I'm just a novice reloader with about 5 years of experience, but it seems common to load more powder into cases with lighter bullets. I always thought the rational was lighter bullets take up less case capacity and that meant more room for powder.

Thanks, Dinny

[gcrank1]

Heavier bullet = more launch inertia thus higher breech pressures. The lighter bullet can use more powder to get to the pressure peak.
FWIW, most accuracy cranks use less than full charge/peak pressure loads.

[quickdtoo]

The problem is 45-70 load data isn't all based on the same maximum pressures, below are the limits set for Marlin levergun pressure in different manuals. Speer and Lyman set the limit at the SAAMI MAP of 28kpsi for trapdoors which really adds to the confusion! 

Tim

Hornady - 40kpsi
Hodgdon - 40kpsi
Speer - 28kcup
Lyman - 28kcup
Sierra - Levergun and Ruger loads are the same pressure
(In the .45-70 case, psi = CUP)

[DCmauser]

Thanks for inputs, I did notice that Hornady seemed to show 'higher' pressures, 25k for trapdoor, while others suggest 18k or less, (40k for marlin vs. 28k by others, as Tim posts above).  Forgot  about the said case capacity effects, even for less than fully charged cases, but those listed were 30~50 grain range, (and no where near compressed).  I should have mentioned the more powder was to attain the same velocities for the 300 & 350 grainers (all same marlin test set-up).  Kinda reverse intuition.
 
I will probably get the 'real' load books from manufacturers and not rely on 2nd source pamplets.

[quickdtoo]

The load book pamphlets are just reprinted data from older sources, you'll find data in them for powders that aren't even published any more by the powder mfrs, to be safe just be sure to start with their recommended start data and work up, using a recommended max with different components and a modern version of the listed powder could be bad. 

Tim 

[twoshooter]

I suggest you start with the latest Lyman manual, they post more pressure data and the widest spread of powders and bullets around. They dont manufacture any components, they just make reloading equipment, so they have some of everything in there, including lots of cast loads.

[gcrank1]

Conventional wisdom for a long time has been to check two, or preferably three sources to confirm data is in the right neighborhood. There have been some NOTABLE misprints in manuals through the years. These sources need to be reloading manuals, not just reprints FROM manuals as you have.

[Ranger99]

all of above.
always err on the side of caution.
always.

[nanuk-O-dah-Nort]

.....  I should have mentioned the more powder was to attain the same velocities for the 300 & 350 grainers (all same marlin test set-up).  Kinda reverse intuition..

DCmauser

remember, there is really nothing set in stone, when you change one  component for another.
as well, burning characteristics are affected by many things.

I'm sure there are many examples that seem counterintuitive.

[gcrank1]

In the Black Powder days 'intuitiveness' worked fairly well, the transition into smokeless resulted in, uh....., some errors.......
Funny thing (not so funny really) is that more than 100years after the introduction of smokeless some of the same assumptions and errors are being made.
Anyone who strays from the sound methodology based on manual(s) data is making the first error, that of thinking/believing that he 'knows' more than the labs that have established the interior ballistic criteria of a given cartridge. This is otherwise known as the 'fools rush in where angels fear to tread' syndrome.
Elmer Keith, and others, were 'successful' in developing wildcats and magnums, but even he/they BLEW UP guns in the process.