Walkalong said:
Pressure, yes, but drag (friction) as well. Factor in the resistance (friction). Try pounding a jacketed bullet through a barrel. It doesn't need pressure to have a lot more friction than lead.
Pressure or Force to physically move the bullet through the bore is different than "Chamber Pressure".
If you look at load data that has both lead and jacketed bullets you will see that often times the lead bullet generated more "Chamber" pressure the same same weight Jacketed bullet.
http://data.hodgdon.com/cartridge_load.asp
http://www.ramshot.com/wp-content/up...ec_1-23-14.pdf
Now if the OP was talking about the amount of force/pressure to physically push a bullet through a bore then, "yes" more force required for jacketed vs Lead. If the OP was talking about "Chamber" pressure then according to Pressure Tested Load data then the answer is "Yes' for this load and "No" for that load, in other words "Maybe.
One theory why Jacketed bullets produce less "Chamber" pressure is "obturation".
A properly sized lead bullet seals off the bore and traps the gasses behind the bullet. A harder jacketed bullet does not seal the bore as well or as completely and gasses can escape past the bullet thus reducing "Chamber" pressure.
Take a look at Hornady #7 45 ACP data for example.
230gr FMJ COL = 1.230. This bullet measures .651 inches.
230gr Lead RN = 1.245. This bullet measures .640 inches.
So the Jacketed bullet is .011 longer and is seated .015 deeper, for a total of .026 deeper.
Data.
N-340 Lead, Max = 6.6gr. Jacketed. Max = 6.7gr.
Even with the .026 deeper the jacked bullet used more powder to reach similar pressure as lead.
Clays Lead, Max = 6.2gr. Jacketed. Max = 6.4gr
Even with the .026 deeper the jacketed used more powder.
231 Lead, Max = 6.2gr. Jacketed. Max = 5.7gr
Here the Lead bullet with less seating depth used more powder. Maybe due to COL, maybe due to the lead bullet.
Unique Lead, Max = 6.3gr. Jacketed. Max = 6.1gr
Again we have more powder with lead than we do with Jacketed.
We can also look at Speer #13. They list their 230gr L-RN at 1.270 COL and their Jacketed 230gr TMJ at 1.260. I do not have the length of the L-RN compared to the TMJ, but of the five(5) powders that are used for both the Lead bullet used significantly less powder than the Jacketed TMJ.
All we have to go on as handloader is load data. Theories are great and often times helpful, but when they conflict with actual pressure tested data, it's best to follow the data and not the "Theory".
So far I have seen no evidence here that Lead bullets build less pressure than jacketed. I have seen lead more, lead less and lead the same. I have seen lead bullet seated deeper producing more pressure, less pressure and again the same pressure.
This is from John Barsness of Handloader Magazine.
"Normally a lead bullet of the correct diameter and hardness produces more pressure with the same powder charge, because it does seal the bore better."
More data that shows Lead produces more Chamber pressure.
This is also from John Barsness.
Here's somedata from Hodgdon's website:
.44 Magnum handgun--
240 cast/ 22.0 IMR4227/ 33,300 CUP
240 jacketed/ 22.0 IMR4227/ 28,400 CUP
.38-55 rifle--
250 cast/ 27.0 H322/ 27,000 CUP
255 jacketed/ 27.0 H322/ 25,500 CUP
250 cast/ 24.0 IMR498/ 36,200 CUP
255 jacketed/ 24.0 IMR4198/ 31,400 CUP
Please not that even though the jacketed bullet in the .38-55 weighs 5 grains more, pressures are less with the same powders charges. And in all the above instances, the STARTING load with jacketed bullets is the MAX load with cast bullets.