Cast bullets create higher pressure?

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.

I don't have that book but all it would take to get higher pressure from a cast bullet is to have it seated deeper in the case...there are so many more variables with cast bullets especially the ones I cast and size it really depends on the testing variables at the testing lab...

Yes, deeper in the case could do it, one of the variables. The bearing length of bullets count in as well, or the hardness of the bullet....................

The manuals are a great start & a chronograph can can offer clues. Part if the intrigue & enjoyment of reloading.

The Jacketed bullets don't completely obturate the bore where as lead generally does.
gramps

Short answer; Nope...

I'm incline to call reconstituted bull fodder. Bravo Sierra if you prefer. Consider this; two 158 gr. bullets, one cast lead, one factory jacketed. Odd are their length would probably for all practical purpose just about equal. Seated to the same depth I believe the lead bullet would show equal or less pressure for the following reason. Lead is soft while the jacket of a bullet is much harder to engrave into the rifling. I can't remember when I last shot a jacketed bullet in my .357 Mag. but I do recall shooting some jacketed factory vs my cast bullets in a .44 magnum. I was using Elmer Keith's load of 22.0 gr. of 2400 powder for both loads. Brass from the cast loads literally fell out of the chambers while the jacketed loads needed a somewhat stiff push ejector rod. This was using an S&W M629 and a Ruger Super Blackhawk and firing both type loads in each. FWIW, the factory bullet was a 240 gr. Speer and my cast bullet which weigh 250 gr. in my alloy. Whether that proves anything or not I guess is irrelevant bull Alliant and Speer are owned by ATK IIRC and neither one sells cast bullets.
Paul B.

I have always found cast bullets to produce less pressure that jacketed bullets--all other factors being equal. Seating depth could cause higher pressures, as has been stated above.

Also,in the opening post, the pressures cited would be considered very much the same for both loads and being within the statistical variance parameters for that pressure level.

So why are there different powder recommendations for the same weight projectile in cast vs jacketed? Sizing of Jacketed runs .429, while cast is .01 or greater, ie .430 in my RedHawk.
gramps

Those pressures may be about the same but the cast bullet load was 1 full grain of powder less than the jacketed bullet. A pretty large percentage difference in charge. I have seen this pressure difference before in the data and wondered about it?

gramps said:

So why are there different powder recommendations for the same weight projectile in cast vs jacketed? Sizing of Jacketed runs .429, while cast is .01 or greater, ie .430 in my RedHawk.
gramps

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Gramps, I size my .44 caliber bullets to .431" and my .38 caliber bullets to .359".
Paul B.

woodperson said:

Those pressures may be about the same but the cast bullet load was 1 full grain of powder less than the jacketed bullet. A pretty large percentage difference in charge. I have seen this pressure difference before in the data and wondered about it?

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I've never figure that out myself. I run either the jacketed data or cast data in my handguns loads using whichever it the greater. I haven't had a problem doing that since 1954. Use your own best judgement on a situation like this. Now to be perfectly honest, I'm more inclined to reduce the max for jacketed bullets than the other way around. :shock:
Paul B.

Paul B said:

gramps said:

So why are there different powder recommendations for the same weight projectile in cast vs jacketed? Sizing of Jacketed runs .429, while cast is .01 or greater, ie .430 in my RedHawk.
gramps

Click to expand...

Gramps, I size my .44 caliber bullets to .431" and my .38 caliber bullets to .359".
Paul B.

Click to expand...

Why? I sized my cylinder throats to come up with what size cast to use in my guns. An RedHawk and NMSBH.
gramps

Gramps, I have severn handguns in .44 magnum Two require that .431" size and it works fine in those that don't. One size fits all. :lol:
Paul B.

Looking at Lee's Modern Reloading, recommended starting loads for all powders for .38 special and .357 magnum all seem to start lower for lead bullets than jacked of the same weight. Most show lower maximum loads too, although a couple actually show greater maximum loads for lead bullets. I assume there is a lot of objective research behind these numbers.