Pressure - Lead / Jacketed ?

[Bullet]

In another thread there was mention of lead bullets creating more pressure than jacketed bullets (shot out of pistols with the only difference being bullets) but the topic wasn’t really about this so I started this thread to see if someone could explain this. Below is part of the other thread.

I thought you got higher pressures shooting lead because it's softer (makes a better seal or a faster seal than copper).

I'm not a physicist or engineer though.


Regardless of seal, lead is softer and has a lower coefficient of friction than copper/brass alloys used in bullet jackets. So shouldn't the lead bullet move forward easier than jacketed and thus tend to lower pressure? From the few high speed pictures I have seen of bullets exiting muzzles, there didn't appear to be much (if any) gas escaping before the bullet came out. I REALLY would like to hear from anyone who can explain the physics of this issue.

 

[ChristopherG]

Bollocks.

Given equal pressure, lead bullets go faster. Which is to say, given equal velocity, pressure with lead is lower.

Assuming, of course, both (the jacketed and lead bullets in question) are suitably sized for the gun and of the same weight.

 

[Bullet]

“Given equal pressure, lead bullets go faster. Which is to say, given equal velocity, pressure with lead is lower.”

This is not what I mean. I mean with the same powder charge the same case the same primer the same bullet weight the same OAL which will create the HIGHER PRESSURE (not fps) lead bullets or jacketed bullets and why?

I know this is a hypothetical question.

 

[ChristopherG]

Hmm. Well, truth be told, if I look at my only manual that gives pressure ratings (and it has lots of comparable lead and jacketed loads--Lyman 2nd ed.), it doesn't look like there's much of a difference one way or t'other in the case you describe. Pressure for a given powder charge and bullet weight looks about identical; the lead bullet is just better at turning that pressure into velocity.

 

[The Bushmaster]

Leading of the barrel and turns (twist) per inch have a lot to do with the difference in powder charges. As far as pressure is concerned...It doesn't matter what you plug the barrel with the pressure will be the same. You will note that lead bullets usually have a longer bearing surface then copper bullets. I doubt that it takes anymore pressure to send a lead bullet down a barrel then it does a jacketed bullet...My two cents for what it's worth...

 

[Grump]

I know this is a hypothetical question.

NO, it's NOT.

Study the Winchester reloading guide. The last time I looked, they gave pressure figures. When you are within 2-3,000 PSI of Max, I don't recommend going up another .1 of a grain of powder. I looked at pistol loads in those rare instances where the same bullet weight was listed for lead and jacketed, and the difference ranged from 0% to 5% LESS powder to reach max pressure when using lead bullets.

Same for the Alliant reloader's guide.

Same when I tried to use the same WW-231 load for 9mm with 115-gr bullets. Was okay with jacketed, showed +P or better pressure signs with hardcast lead (based on firings of +P ammo, compared with standard ammo--same case, same primer, same guns). The lead one also went 75-100 fps faster. I'm NOT loading any more of those, thank you!!!

 

[Ben Shepherd]

Here's the easy way to answer:

If everything else is identical, the jacketed version will create higher pressure.
Why? Because the copper jacket creates more friction/resistance in the bore than the softer lead does.

'Course even if the slugs are the same weight, if they are a different shape, with a diferent amount of bearing surface, the above statement goes out the window

 

[happy old sailor]

i read an article that stated that depth of seating had a greater effect on pressure than about anything. identical load with deeper seated bullets had greater pressures by reason of less combustion space in said cartridge. this is ballistic laboratory stuff that i do not have access to otherwise i would post my own findings. i feel discussion on this subject to be near critical to the handloader. i have paid more attention to this than i did as a result of that article. what have i learned?, absolutely nothing. yep, i needf a lab.

 

[Ol` Joe]

Study the Winchester reloading guide. The last time I looked, they gave pressure figures. When you are within 2-3,000 PSI of Max, I don't recommend going up another .1 of a grain of powder.

The test bed Winchester used isn`t the same as yours and the data isn`t really valid out of their lab. The pressure finding in a lab are fairly close estimates of what your pressures really are. You don`t really know what your pressures are unless you have test equipment, and if so it will be a simple matter to check your loads to see for yourself if one is showing more pressure then the other.

There also is the fact PSI shown in the books are recorded highs, NOT acual fixed pressure. There is some variation in like loads that can show quite large spreads in pressure. The factories load to a max allowed PSI and list the high as the pressure of the load but the average might well be 3K less then the max recorded. -even more in a rifle load- Remember SAAMI lists the max as the highest allowed pressure not the average. I don`t think though there can be a fixed "this will give more pressure then that" answer to the lead vs copper debate. There might be things like pressure "spikes" or other events that cause one to show higher pressure then the other in the books, in some cases. Then again I`ve heard rumor of some companies useing computer pressure models as their data source...

The jacket material commonly used today is not as "slick" as lead and depending on alloy the lead bullet should be easier to engrave when it hits the leade. If this is true then jacketed bullets SHOULD give higher velocity due to higher pressures. They should also give higher pressures with like powder charges. Velocity is directly related to pressure, you won`t get higher vel with lower pressure no matter how slick the bullet as long as pressure is higher then needed to prevent the bullet from slowing due to drag. As long as there is pressure on the bullet it will keep speeding up at a rate governed by the push on it.

I guess what I`m saying is don`t excede the books loads with as near to the same components as possible, and if you have a crono you can likely figure if your velocity is higher then the books the pressures are also. I also don`t believe with todays many alloys any one answer will be true in all cases, don`t try subbing one type for another just because it "should" be slicker.

 

[Grump]

Tried to edit typo and got a double post...

 

[Grump]

Here's the easy way to answer:

If everything else is identical, the jacketed version will create higher pressure.
Why? Because the copper jacket creates more friction/resistance in the bore than the softer lead does.

Does that assertion jive with any published pressure figures from any powder or bullet manufacturer? Look, for example at the Alliant Reloader's Guide for .40 S&W 155-gr lead Laser-Cast: http://recipes.alliantpowder.com/rg...idgedescr=S&W Auto&bulletdescr=Laser Cast 180
Unique 5.5gr 973fps 32,700 psi
and compare with 155-gr JHP from JHP:
http://recipes.alliantpowder.com/rg...0&cartridgedescr=S&W Auto&bulletdescr=180 JHP
Unique 6.4gr 1,065fps 33,800 psi

Now, since each of these is the max load, we *might* safely *assume* (with all risks, of course), that there were unacceptable pressure variations at .1 grain of powder higher than the maximum allowable MAP or whatever statistic for max pressure they are using for a standard. The test beds were the same. Am I to believe that the 155-gr lead bullet produces LESS pressure with an equal powder charge than the 155-gr JHP? The JHP is longer than the solid lead laser-cast, so it is likely to be seated deeper at the bullet base for the same OAL, listed as the same for each load. We don't know for sure whether there is a significant difference in bearing surface, but the Laster-Casts I shot actually had a little less than the Hornady JHPs I also loaded in the .40.

So, I think we have a .9 grain difference in maximum powder charge that is but one example of how a lead bullet will produce higher pressures than a jacketed one.

Explain things based on the science of observation, please. Theories don't mean squat unless they can explain the real-life experience.

 

[Ben Shepherd]

Not flaming or anything else- but yes my information jives in several of my manuals-you have found an instance in which it doesn't- I can find several in which it does. Mostly magnum stuff, I'll admit, 9mm isn't something I load a ton of.

I stand by my statement-but with all availible variances it's not an absolute- as I noted and you proved.

 

[AFhack]

Ben has it right...

easy visualization: take a .45 inch hole in a piece of steel. Then take a hammer and pound a .452 inch piece of copper thru the hole. Then take a hammer and pound a .452 inch piece of lead thru the hole. Which one took more pounding to get thru the hole?

The copper one did.

 

[danhei]

Reloader's Guide for .40 S&W 155-gr lead Laser-Cast: http://recipes.alliantpowder.com/rg...idgedescr=S&W Auto&bulletdescr=Laser Cast 180
Unique 5.5gr 973fps 32,700 psi
and compare with 155-gr JHP from JHP:
http://recipes.alliantpowder.com/rg...0&cartridgedescr=S&W Auto&bulletdescr=180 JHP
Unique 6.4gr 1,065fps 33,800 psi

Those loads are for 180 gr bullets. In any case, I'm not sure how much this is telling. The lead load is for less powder and has less pressure. Does anyone have pressure data for the same powder load with cast and jacketed bullets?

 

[Grump]

The test bed Winchester used isn`t the same as yours and the data isn`t really valid out of their lab.

Do you therefore believe that two loads using the same powder and bullet weight, in the test bed, with one showing higher pressure than the other, would not also fall in the same order of higher-to-lower pressure when fired in another firearm?

Yes, the pressure in *your* gun may be different, and the velocity in *your* gun may be different, but is it not reasonable to expect the higher-pressure load to be higher pressure regarless of what firearm it is fired in?

If your answer is "no", then why bother with reloading manuals at all?

The "test" of hammering a slug through a hole does not necessarily follow. There is a different acceleration mode at play, over shorter time and so strong that the typical lead bullet sorta collapses and obturates into the bore, even if a bit under-sized. My hammer doesn't do that--slugs must be oversized to give an accurate groove dimension.

Citations, please, to where the lead bullet load either:
A. Used the same amount of powder as an equal-weight jacketed bullet, and showed less pressure; or
B. Used more powder than an equal-weight jacketed bullet, and showed less pressure; or
C. Used the same amount of powder as an equal-weight jacketed bullet, and showed the same velocity; or
D. Used more powder than an equal-weight jacketed bullet, and showed less velocity.

Sorry if I linked to 180-gr bullets and called them 155s--the point, however, remains valid for .40 S&W and Unique powder. And that was the first one I looked at.

BTW, the lesser pressure in my cited loads is not significant, when compared to almost an entire grain of powder difference between the loads.

I studied this hard in handgun cartridges a few years ago, and the closest I remember finding was a few max loads that were the same or within .1 grain of powder, when using the same powder and same weight bullet in both lead and jacketed. This was when comparing within the SAME source--IOW, not comparing one test bed with lead with another bullet/powder maker's figures for jacketed.

 

[rick_in_lb]

Good Info

I love it when the Senior Members come out for a topic! All the good info comes out!

 

[Ol` Joe]

Citations, please, to where the lead bullet load either:
A. Used the same amount of powder as an equal-weight jacketed bullet, and showed less pressure; or
B. Used more powder than an equal-weight jacketed bullet, and showed less pressure; or
C. Used the same amount of powder as an equal-weight jacketed bullet, and showed the same velocity; or
D. Used more powder than an equal-weight jacketed bullet, and showed less velocity.

From Hodgdons Annual manual

A.

45acp 200 gr
lead; 8.2 gr HS-6 860 fps @14400 PSI
jacketed; 8.2 gr HS-6 868 fps @14000 PSI

Note; This also pretty much answers C also. Equal powder, equal velocity.

45acp 230 gr
jacketed; 8.0 gr HS-6 790 fps @ 14400 CUP
lead; 8.0 gr HS-6 859 fps @ 16600 CUP

jacketed; 5.4 gr Universal 751 fps @13300 CUP
lead; 5.4 gr Universal 857 fps @16800 CUP

jacketed; 4.8 gr Titegroup 818 fps @16700 CUP
lead; 4.8 gr Titegroup 855 fps @17000 CUP

In these loads lead gives higher psi and velocity then jacketed. Now look at the 44 mag.

44mag 240 gr
lead; 11 gr HP-38 1334 fps @38100 psi
jacketed; 11 gr HP-38 1272 fps @37800 psi

lead; 10 gr Titegroup 1288 fps @ 38400 PSI
jacketed; 10 gr Titegroup 1292 fps @ 37700 PSI

lead; 10.2 gr Universal 1276 fps @ 37500 PSI
jacketed; 10.2 gr Universal 1247 fps @ 38200 PSI

Once more "C" is could be represented with the Titegroup loads, as 4fps means nothing in real life, and the rest show lead as having higher pressure with all else equal except the Universal load which has lead higher in vel with less PSI.

The majority of loads here show lead having higher pressure then jacketed, but I`m sure if I looked I could give similar results with the jacketed comimg out on top. The difference in alloy, bearing surface, ect between one lead bullet and another can vary enough to make any general claim to lead being higher or lower in pressure with the same components questionable. The point is there is no one answer to this. Nothing is ALWAYS true. The manuals are only guides, not cut in stone. The results of our compont lots can vary quite a bit from the manuals and this is why we are constantly reminded to "work up".

Edited to add;
One should read the A-Square manual 'Any Shot You Want" to get a good education on load variance vs pressures. They test primers, powder lots, bullet styles, ect in the lab and show the effects on pressures they found. The book deals with rifles but I don`t doubt the general findings hold true in pistols also.

 

[Vern Humphrey]

NO, it's NOT.

Study the Winchester reloading guide. The last time I looked, they gave pressure figures. When you are within 2-3,000 PSI of Max, I don't recommend going up another .1 of a grain of powder. I looked at pistol loads in those rare instances where the same bullet weight was listed for lead and jacketed, and the difference ranged from 0% to 5% LESS powder to reach max pressure when using lead bullets.

Same for the Alliant reloader's guide.

Same when I tried to use the same WW-231 load for 9mm with 115-gr bullets. Was okay with jacketed, showed +P or better pressure signs with hardcast lead (based on firings of +P ammo, compared with standard ammo--same case, same primer, same guns). The lead one also went 75-100 fps faster. I'm NOT loading any more of those, thank you!!!

Spot on. I once had this debated with Ed (E.C.) Harris, and he convinced me -- lead bullets will develop higher pressures than jacketed bullets, all other things being equal.