Cast bullets create higher pressure?

Seating depth of each bullet, and therefore the case volume beneath the base of each bullet could be a factor.

I dont have the book in front of me but the bullet diameter on lead is also generally a little larger.

Deleted

Lead generally has less resistance and is driven faster if all else is equal . must be seating depth, best I can figure

It would be interesting to know if more force is required to overcome the friction of a lead bullet inside a case mouth, or a copper jacketed bullet.

I can imagine the potential that a lead bullet size 1/1000th of an inch larger in diameter, might have slightly more friction to overcome. Which could result in a higher pressure for the powder charge, despite the lead bullet then moving more easily down the barrel.

Someone probably knows, but it seems it may be very hard to actually measure that.

AJC1 said:

I dont have the book in front of me but the bullet diameter on lead is also generally a little larger.

Click to expand...

Diameter of a lead bullet has almost no effect on pressure. Lyman did a study to find the answers on that.

HHmm,
maybe the lead bullet seals the bore better causing higher pressure,

Dudedog said:

HHmm,
maybe the lead bullet seals the bore better causing higher pressure,

Click to expand...

This is what I've been lead to believe. Doesn't mean it's right though.
It could also be the burn rate of the powder lot.

Why not ask Alliant?

dgang said:

Just perusing 2005 Alliant Reloading Guide for .357 Mag. cast bullets and found some data I don't understand.(not an uncommon state) They give 7.8 gr. of Unique for 158 gr. JSP @ 1280 FPS, developing 33,200 PSI. The same data states 6.8 gr. of Unique for a 158 gr. cast LSWC @ 1295 FPS but with a higher pressure of 33,900 PSI. I can understand the difference in the amount of powder and velocities, but fail to understand why the cast bullet with less powder has higher pressure. Any help out there?
Thanks in advance and good shooting' to ya.

Click to expand...

What were the COL for those loads?

WrongHanded said:

Seating depth of each bullet, and therefore the case volume beneath the base of each bullet could be a factor.

Click to expand...

This would be my 1st answer.

Obturation said:

Lead generally has less resistance and is driven faster if all else is equal . must be seating depth, best I can figure

Click to expand...

Yes, on the nosy, Obturation.

It would be interesting to know if more force is required to overcome the friction of a lead bullet inside a case mouth, or a copper jacketed bullet.

Click to expand...

All else being equal, copper would require more force than lead.

Lead/cast bullets are more efficient than their jacketed counterparts. You can take a jacketed bullet vs cast bullet of the same weight and use the same powder/powder charge and seat the jacketed bullet deeper in the case. The lead bullet will have either equal velocity or more velocity.

The design of the cast bullet and it's ability to have the bottom drive band/bullet base compress also plays a huge role in getting the most out of a load with lead vs jacketed.

I use a 9-ton press to swage jacketed bullets. I use a 1-ton press to swage lead bullets.

It could also be a misprint. I found one in the Accurate reloading data for 35 Remington and called them about it. They confirmed the data was incorrect and sent me a hat and a patch for letting them know. Mistakes happen.