I noticed for example a 357 mag 125 JFP on speer.com needs 7.5 gr of Universal powder for a starting charge 1148 FPS. But on hodgdon.com a 125 cast LRNFP only needs 4.8 grain of the same powder 1046. So I guess you cannot use the same data with different bullet types. Is this because the jacketed bullets need more oomf the get them moving in the first place to get them started?
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Jacketed bullets need more powder than Lead Cast?
- Thread starter BondoBob
- Start date
No, you cannot. It's because the bare lead doesn't do well under that much pressure. You need enough pressure that the base of the bullet will deform and seal the bore, but not too much that you get that gas blasting through and little crevice it sees, which also subsequently sprays the bore with molten lead. Not good.
Those numbers are totally subjective of bullet to bore fit and lead hardness.
Sent from my SM-G975U using Tapatalk
Those numbers are totally subjective of bullet to bore fit and lead hardness.
Sent from my SM-G975U using Tapatalk
From years of chronographing, I can say without any doubt that jacketed or plated bullets need more propellant to achieve the same velocity (all else being equal, or course).
It's important to understand that doing so also increases the peak pressure; or viewed from another angle, the actual burn rate of the propellant increases. An important concept to grasp.
It's important to understand that doing so also increases the peak pressure; or viewed from another angle, the actual burn rate of the propellant increases. An important concept to grasp.
black mamba
New member
Yes, lead bullets are "slipperier" than jacketed so give more velocity for the same charge, but the pressure of both loads is still pretty close. To get the same velocity from jacketed you need more powder at higher pressure to overcome the higher friction.
First point, lead bullets are "softer" and so squeeze down the bore "easier".
Next point, about the starting loads, what you're looking at is the starting point chosen by two different groups of testers, using two different bullets with different intended uses.
Most people shooting a .357 JSP will want it faster than a cast slug of the same weight, and so a higher level starting point makes sense.
Just because 2 bullets have the same weight doesn't mean all data for them is identical or interchangeable.
And that applies to jacketed bullets as well. Multiple factors including bearing surface area, material it is made of as well as bullet to bore fit all play a part.
Next point, about the starting loads, what you're looking at is the starting point chosen by two different groups of testers, using two different bullets with different intended uses.
Most people shooting a .357 JSP will want it faster than a cast slug of the same weight, and so a higher level starting point makes sense.
Just because 2 bullets have the same weight doesn't mean all data for them is identical or interchangeable.
And that applies to jacketed bullets as well. Multiple factors including bearing surface area, material it is made of as well as bullet to bore fit all play a part.