Is how much smokeless powder equivalent? My 470 is proofed"75 cordite and 500 grains

IMR3031 traditionally regarded as grain for grain with cordite for safe starting loads, if anything slightly slower so usually have to increase load if using this smokeless powder.

Here is data from old Elmer Keith for loading the British big bores converting from cordite with the smokeless powders of the day.

x1.33 for IMR 4831 is a good starting place.
Cal

So is the proof load the standard load? Or max load? What does 75 grains of cordite get a 500 grain pill up to speed wise?

The 75-500 MAX is the cordite charge and bullet weight to use. The proof load was much higher in pressure via increased powder charge and/or increased bullet weight, or both. The velocity was taken using the standard load (not the proof load) but from 28" barrels (to add a bit of blue sky to the figure).
Perhaps a better term to use would be regulated load of 75-500 MAX.
Cal

I find RE15 very useful. Will look up the cordite conversion. Using Kynoch foam wads in the larger cases.

1.19 for cordite to RE15.

This written up by Graeme Wright ( Shooting the British Double Rifle) as coming from Ross Seyfried, but Ross wasn’t the originator.

Not exact, is rifle dependent like all data.

Cheers, Chris

Here is a rough equivalent table I made several years back.

Cordite Ratio

I7828=1.40
RL22= 1.37
S-385=1.35
I4831=1.33
I4350=1.25
S-365=1.24
RL15 =1.19
S-355=1.17
I3031=1.10

Just a suggestion: avoid IMR3031
Even though Elmer Keith and Jack Lott used it in the 1970’s and early 1980’s the powder has since that time been implicated in burst or wrecked nitro express rifles. 3031 is said to be very sensitive to pressure excursions with even minor variations in charge weight, seating depth, etc.
Graeme Wright’s book is a better and more modern source for reloading the nitro express cartridges.
- Mike

I use 3031 in a load that I developed for a double rifle, and I agree that I would avoid using it for your application. It is also very sensitive to heat, such as do not allow unfired rounds that are loaded with 3031 to remain in a hot DR prior to firing them. I speak from experience.

Keith, sometimes, wrote bullshit. As a Brit who corresponded with Eley Kynoch forty plus years I can tell you that "cordite" is as imprecise a term as "smokeless powder".

There was NOT one cordite that was loaded into each and every single British cartridge by a simple weight recipe.

So no, they cautioned, I could not just dismantle 303 cartridges and use the resulting cordite to reload with by taking that weight of cordite extracted from a 303 to use to match the cordite load marked on, say, a 470 as its standard (weight of cordite) load.

Just as there was not, and isn't, one smokeless powder that is loaded into every single Winchester loaded cartridge by a simple weight recipe.

So just as there was and is 4895, 4350, 4831 and Bullseye and HP-38 so there were, in fact different cordite powders. With different burn rates.

And the cordite in a 303 isn't the same as the cordite in a 600 and neither the same as the cordite in a 375.

And that's before it gets complicated with the use of chopped cordite. Essentially cordite is a broad term to refer to a powder extruded in lengths.

Revolver and pistol cordite was chopped. It looks like, say, HP-38, but yellow brown, but still resembling fine disks.

At the extreme gun (as in 25 Pounder Gun) cordite looks like uncooked spaghetti. Just as thick, just as yellow.

Like a rope. Or cord. Thus cordite. So just as rope describes anything from string to full on 2" thick rope... ditto cordite.

So the old Eley Kynoch loads would be XX grains of Cordite #Z or YY grains of Cordite #Z or XX grains of Cordite #W or YY grains of Cordite #W.