What's the rule on adjusting jacketed load data to cast loads?

[tacotime]

I have some good mid-range loads (say, under 1600fps) for 45-70 and 458WM using the 350 and 405 grain jacketed bullets.  But I don't see similar mild loads for same weight cast bullets using the powders I already have (4198, 4064, 3031, Rel7, H4895).  Is there a safe rule for adjusting jacketed loads to cast loads for the same bullet weight and same powder?  Knock off a grain or more maybe?

Thanks.

[SHOOTALL]

If I were you I would get a good book for loading cast bullets or check out the Winchester , IMR, hodg. site. Changing a componet can effect alot

[stimpylu32]

In MOST case's , you can use the same data for Cast that you use for Jacketed , this is because the cast bullet will have less drag and in turn will allow for less pressure to build - However going the other will can cause major pressure problems !

Other factors have to be taken in to account , like speed of the round , OD size of the bullet , you get the idea . A good rule of thumb is to drop back 5% and re-work up the load .

stimpy

[yardmaster]

The Lyman cast bullet guide is a good one.. lots of good info and loads all in one

[McDerry]

For the 45/70 Lee list h4198 with a 405 lead at 27 grains start at 1289fps and 31 max for 1459fps.  Hodgdon also list one with 4895 with the 405 gr bullet.

[bilmac]

What Stimpy said, plus if you want to keep the velocity the same then you will probably need to reduce the charge a bit.

[tacotime]

Ok.  And since I am using a Ruger 3 and some medium level loads (really in the trap door range near 1500fps) and some reduced loads using H4895 (which is suitable for reducing so says Hodgdon, and I have done it successfully) my current theory is that using a cast bullet of the same weight as the jacketed, even at the exact same charge, should by no means go above acceptable pressure, even if a little faster. Does this theory scare anyone?

But I plan to reduce the load anyway.  Hornady shows about 52 grains of H4895 on a 350 jacketed at about 1500.  So I could dop off to about 50 for the cast.  But 50 is already a load I'm also using with the 350 jacketed!  So I think I'm safe range since the max load for 1895's is shown at almost 59.  And those are below the Ruger levels.