Charge weight differential question

[tomf52]

By looking at some different pistol loads, I have established mathematically that there is about a 15% difference (average) in powder charge weights from jacketed to lead bullets in most calibers, the bullet wights being the same and the lead being the lowere value. Is this a correct assumption or out in no no land? Example: Hodgdon book says start with 3.8 gr W231 for 158 gr Jacketed and 3.1 gr W231 for 158 LSWC. The actual diiference of this load is closer to 18% but the overall average comes out around 15% for different loads in their book of the same weight bullet between jacketed and lead. What I am trying to determine is resonable starting loads for lead when I can only find posted loads for jacketed. Thank you for any help here.

[badgeredd]

By looking at some different pistol loads, I have established mathematically that there is about a 15% difference (average) in powder charge weights from jacketed to lead bullets in most calibers, the bullet wights being the same and the lead being the lowere value. Is this a correct assumption or out in no no land? Example: Hodgdon book says start with 3.8 gr W231 for 158 gr Jacketed and 3.1 gr W231 for 158 LSWC. The actual diiference of this load is closer to 18% but the overall average comes out around 15% for different loads in their book of the same weight bullet between jacketed and lead. What I am trying to determine is resonable starting loads for lead when I can only find posted loads for jacketed. Thank you for any help here.

Does that reduction hold true for other calibers and for slower powders?

I've been reducing powder quantities by a less scientific means....generally I go to the mid-range burn rate powders and reduce the load by 15%. So far it has worked out pretty decent as a starting point.

The reason I go to the mid-range powders is I don't want to get into the really slow powders because of the SEE thing. And the fast powders are way too easy to get too much bang in a short time!

If your hypothesis holds true, it would be a good rule of thumb for starting a load.

Edd

[MtGun44]

Lead alloys have a low coefficient of friction against steel. This is part
of the reason that plain bearings are coated with babbit (tin-lead alloy).
I have also noted higher velocity with lead boolits of the same wt as
a jacketed in magnum handguns, and I presume this is due to the lower
friction. Your observation is consistent with this, and it would look
like a good plan to us some reasonable reduction like 15% when using
jacketed data for lead boolits.

I do not think this is a safety issue, since the same wt boolit and lower
friction does not seem to be likely to increase pressures, but probably
the same or lower pressures for greater velocity.

Bill