Pressure in Cast vs Jacketed Bullet Loads

[GyMac]

All my shooting life I have believed that when it comes to loading cast vs jacketed bullets, all things being equal, the cast bullet load will achieve higher velocity with lower pressure. Recently, though, I have encountered the opinion that lead bullets actually increase pressures as they form a better seal and it's this increased pressure that leads to higher velocity. I still think I'm right, but some of the arguments have led me to question my beliefs. Please give me your opinions (or better some facts) on this. Thanks.

 

[David R]

Ever slug your bore with lead? Try it with a jacketed bullet. It will drive through MUCH harder. This is where I think the increased pressure comes from.

Data: Look in the lyman handbook. By switching from Jacketed bullets to lead for the same weight 75 fps are gained with the same pressure limit. This is in 38 special caliber.

David

 

[Yorkie Man]

Pic up the book "Understanding Firearms Ballistics" by Robert A. Rinker it is an eye opener.

 

[Nevada Ed]

maybe...........
until you try to shove too large a lead bullet down your barrel,
which could shoot those pressure numbers up in a hurry.

Small details is what it is all about..................
.001" or so.

 

[Rule3]

Pic up the book "Understanding Firearms Ballistics" by Robert A. Rinker it is an eye opener.

Please share.

 

[Rule3]

Ever slug your bore with lead? Try it with a jacketed bullet. It will drive through MUCH harder. This is where I think the increased pressure comes from.

Data: Look in the lyman handbook. By switching from Jacketed bullets to lead for the same weight 75 fps are gained with the same pressure limit. This is in 38 special caliber.

David

Where do you find this? Under a specific load?

"All things equal", is the powder charge the same??

I don't know. I have substituted lead bullets for fmj using the fmj data and velocity will increase. I have no way of course to measure pressure.

All load data in manuals is calculated to fall at or below pressure specs for the cartridge. Regardless of the powder most pressures listed will be almost the same give or take a bit.

 

[YARDDOG]

Where do you find this? Under a specific load?

"All things equal", is the powder charge the same??

I don't know. I have substituted lead bullets for fmj using the fmj data and velocity will increase. I have no way of course to measure pressure.

All load data in manuals is calculated to fall at or below pressure specs for the cartridge. Regardless of the powder most pressures listed will be almost the same give or take a bit.

Exactly what I've noticed ; )
Y/D

 

[GyMac]

The reason I asked was that I have always been under the assumption that if you have load data, for example: a 95 grain FMJ roundnose, but not for a lead roundnose - that it is safe to take the starting load for the jacketed bullet and use it for lead. But when I was reading internet postings (I know, I know) I was surprised to find many people advocating taking the starting data for jacketed bullets and cutting it 10% and then working up. This, due to the higher pressures caused by lead projectiles. This runs counter to what I have always believed about lead bullets.

 

[GyMac]

maybe...........
until you try to shove too large a lead bullet down your barrel,
which could shoot those pressure numbers up in a hurry.

Small details is what it is all about..................
.001" or so.

This is true! I almost always shoot .001 over in lead but bore diameter in jacketed. Still, I thought the lead will relatively easily swage down and create less pressure than a jacketed bullet.

 

[David R]

Lyman # 47 38 special

158 JHP max velocity any powder in this case AA5 821 fps 16,300 C.U.P..

5.0 unique 710 fps 16,600 C.U.P.
7.1 Blue Dot 721 fps 16,300 C.U.P.


158 lead round nose max Velocity
7.8 Blue dot 919 fps 16,400 C.U.P.
5.1 unique 896 fps 16,400 C.U.P.

SO the way I see it same pressure, more Velocity with lead in 38 special. Not the same in all calibers.

David

 

[Rule3]

Not exactly the same powder charge but pretty darn close at least for Unique. The Blue dot is .7 grains more but still a lot more velocity.

Interesting. Thanks!

 

[Alk8944]

While it can be problematical to to make generalizations in this circumstance there is one loading manual which I believe can be trusted for pressure data. This is the old large format Hercules/Alliant manual. If you have access to one it gives a quite straight comparison between Lead and jacketed bullets of the same weight.

The general difference that can be seen in Alliant is this:

1) For a given caliber all loads are shot in the same barrel and same primer.

2) Usually the Lead and jacketed data will be identical or varying by no more than .1 grain charge weight. Depending on the specific propellant the heavier charge may be either for Lead or jacketed.

3) Given the same propellant the pressure difference between Lead and jacketed is no more than a few hundred PSI. Doing a quick skim of .38/.357 data the greatest pressure difference found was 900 PSI. The higher pressure may go either way!

4) Given loads which are virtually identical the velocity always goes to the Lead bullet, usually by ca. 120-125 FPS. Note: This matches my own experience chronographing handloads.

5) Alliant data totally disproves the popular belief that the same charge weight cannot be used for both Lead and jacketed bullets! Leading with swaged or cast Lead bullets is more a function of bullet fit and lubricant efficiency, alloy and velocity are secondary.

Not related to the original question, but so you get leading with Lead bullets! SO WHAT! Clean the gun. If you have a load that leads then carry a rod and bronze brush with you when shooting. Brush the bore every 2-3 cylinders full and you have beat leading before it gets started. 4-6 in & out passes will do the job.

 

[fredj338]

I am one that believes pressures with lead bullets are slightly higher with the same powder charge wts. While lead bullets are more malleable, they do provide Better seal if properly oversized. Lead also has a higher coef of friction over gilding metal, but often less bearing area, so pressures are only slightly higher. It's why you use lower charge wts for lead vs jacketed. Until someone with pressure gear proves otherwise, that's my view.

 

[David R]

Lyman #47 again, 45 automatic

185 lead 7.5 grains Unique 995 fps 15,500 C.U.P.
185 Jacketd metal case wadcutter 7.5 grains Unique 1055 fps 18,000 C.U.P.


One more example
200 grain lead bullet #452460
7.5 grains Unique 980 fps 16,600 C.U.P

200 grain lead bullet #452630
7.5 grains Unique 913 fps 17,400 C.U.P

Just lead bullet design.
Lyman also used Federal cases with bullet 452630. This could also change results.

David

 

[Forrest r]

Interesting reading, might as well put my 2 cents in.

The seating depth/case capacity has more to do with pressure than bullet fit/type of metal/etc.

Traditionally a lead bullet of the same caliber/same weight will be longer taking up more case capacity when it's seated to the same oal. In cases with bigger case capacity or low pressure calibers (38spl/44spl/45acp) are more forgiving. 9mm's & 40s&w's are another story as are the 38 supers & everyone reads about allot of kabooms (#1 reason, bullet setback from wrong/bad crimp//// setback ='s bullet being seated deeper/less case capacity) in those calibers.

As far as lead causing more pressure from being oversized. No way!!! Anyone who casts & sizes their own bullets knows better. I use a 1/2 ton press to size hard cast lead bullets up to 3/1000ths smaller. I also swage my own bullets & use a 9 ton press to make/swage them (easier on the rock chucker with an extended 2' shovel handled arm).

To anyone who doesn't think lead takes less pressure to drive down a bbl. I have a take-off 308 bbl that has a 308 bore & 300 grooves. I'll give you a 200gr jacketed (.308) bullet, a steel rod & a 20oz hammer and have you drive that bullet down the length of the bbl. Then you can try with a 200gr lead bullet (.311) that's 3/1000ths larger in diameter & have you do the same thing, drive the bullet down the length of the bbl with the same tools. It won't take long to figure out which one is harder/takes more pressure to drive down the bbl. And that's with a jacketed bullet the same size as the bore & a lead bullet 3/1000th's oversized.

Lead bullets really shine in snub nosed/short bbl'd pistols & revolvers. That extra velocity makes a huge difference.

 

[GyMac]

Good and interesting posts, all. My reason for posting in the first place was the discrepancy I found in data for .380 95 grain bullets. It wasn't an issue of safety, I just wanted to duplicate factory specs with a lead bullet. But some of postings I read made me question some of the things I thought I knew about lead bullets. I've always loaded lead and will continue to do so. Thanks for all the posts.

 

[Jellybean]

Gymac, I've tried to answer this twice and both times it disappeared while I was typing, so you are going to get a quick answer.

You were right. It is almost impossible to find data where everything is the same except for lead or jacketed bullets. But the proof you were looking for is found in comparing a jacketed bullet to the exact same bullet that is Teflon coated.

I read Robert Rinkers book too, I don't recommend it to anyone.

 

[Maximumbob54]

Gymac, I've tried to answer this twice and both times it disappeared while I was typing, so you are going to get a quick answer.

You were right. It is almost impossible to find data where everything is the same except for lead or jacketed bullets. But the proof you were looking for is found in comparing a jacketed bullet to the exact same bullet that is Teflon coated.

I read Robert Rinkers book too, I don't recommend it to anyone.

Just curious but why not?

 

[Jellybean]

For two main reasons...

There is a big difference between someone that is educated on a subject and writes a book for the layman to understand, and a layman that writes a book about a subject he doesn't understand.

In the beginning of the book he states that it will not be based on rumors or unproven facts, then he uses the rumors and unproven facts to validate his opinions.

I don't have a lot of books in my handloading/ammunition library, at least I don't think so, but there are some I treasure, some that are about average, some that are sort of alright and some that I don't read very often. But there were only two that I had absolutely no use for, regret having had to pay money for and do not recommend to anyone else, this one and "Reduced Load Ballistics Research Manual" by Tom Halstead, AAGSR. I've filled the gaps on my shelves with e-books on CD's for now.

 

[gen3guy]

Is it not possible that different bullet types (cast, jacketed HP, etc.) will vary case volume depending on how they are seated and crimped? Volume should have a direct effect on pressure. I do a lot of reloading but I never get close to maximum powder charges so I don't think about it much. Perhaps I should.