MV of cast vs. Jacketed bullets

[DWalt]

Just as a matter of possible interest to some, I made up a dozen each loads consisting of 158 grain bullets (lead SWC and FMJ) in .357 Magnum cases, using 7.0 grains of Unique (weighed), with maximum COAL. In firing, I used my pristine Colt .357 Trooper with a 4" barrel. Cases had mixed headstamps, and I used all chambers, to simulate reality. I chronographed these loads, and dropped the maximum and minimum MVs for each, leaving a 10 shot group for each to perform statistical analysis.

1. 158 grain lead SWC: Average MV = 1103 ft/sec, SD = 38.3 ft/sec

2. 158 grain FMJ: Average MV = 1016 ft/sec, SD = 18.4 ft/sec

Therefore, for this load, the MV difference is 87 ft/sec, in favor of the lead bullet. I am surprised the SD was so much greater for it vs. the FMJ.

 

[Doubless]

You really shouldn't be.. lead has a sort of lubricating quality to it. I can't explain it, but it is a fact. Additionally, lead is softer than copper, and as a result there is less friction. Less friction means higher velocities, at least in my mind.

 

[Snapping Twig]

Cast = higher velocity for any given powder weight over jacketed.

Kinda why I like cast.

 

[Alk8944]

Yup! I have posted numerous times that on average the velocity difference between a cast bullet and a jacketed one is 100 FPS +/-. It always favors the Lead bullet. You are right there! This isn't guessing, it's a result of chronographing literally thousands of rounds.

 

[fredj338]

You really shouldn't be.. lead has a sort of lubricating quality to it. I can't explain it, but it is a fact. Additionally, lead is softer than copper, and as a result there is less friction. Less friction means higher velocities, at least in my mind.

Many say this but think about it, if the bullet was slicker, vel would be less. You see this in moly coated bullets, less vel with identical charge wts. I believe it is the softer alloy creating higher friction thru greater bore seal, higher pressure & then higher vel. More maleable yes, but slicker, not really. Some day I'll have a pressure trace & can prove this.

 

[S&WIowegan]

I also suspect that Colt 3-5-7 has a pretty tight bore which tends to raise pressure and velocity. Or put another way...a worn bore will tend to give lower velocities than a tight new bore. Pythons are rather famous for tight bores.

 

[Calliope]

I believe it is the softer alloy creating higher friction thru greater bore seal, higher pressure & then higher vel.

If that were true then why wouldn't plated bullets be as fast or faster than lead? They have soft cores (most brands) and only a thin plate of copper, so they should fill the bore and seal like lead. But they always test slow like jacketed.
I think (guess) that pressures are similar in all the loads and the lower friction bullets like lubed lead and powder coated lead gain more velocity. Copper has high friction, whether it's thinly plated over a soft core or in a heavy jacket, so it's slower.

 

[Forrest r]

Lead is a lubricate all by itself.

Less friction ='s more velocity

I've tested jacketed, lead with traditional lube & powder coated bullets by swaging my own bullets with the same shape/design for the 35cal's, 44cal's and 30cal's.

In every test the powder coated bullets had the highest velocities. Followed by traditional cast/lubed lead bullets and then jacketed.

 

[fredj338]

If that were true then why wouldn't plated bullets be as fast or faster than lead? They have soft cores (most brands) and only a thin plate of copper, so they should fill the bore and seal like lead. But they always test slow like jacketed.
I think (guess) that pressures are similar in all the loads and the lower friction bullets like lubed lead and powder coated lead gain more velocity. Copper has high friction, whether it's thinly plated over a soft core or in a heavy jacket, so it's slower.

Well they are faster than jacketed, hence my theory it is a better bore seal increasing pressures. Again, lower friction bullets do NOT gain vel. Look at the Barnes manual. They have data for identical bullets but foe their moly coating. The slicker buckets require more powder to achieve the same vel. Less friction, lower pressure. I suspect using bullets 0.001-0.002" larger also increases bore seal & raises pressures. It is my theory, based on available data & my own vel testing. Without pressure data, hard to prove, but the slicker bullet theory has already been debunked in the Barnes manual.

 

[fredj338]

Lead is a lubricate all by itself.

Less friction ='s more velocity

I've tested jacketed, lead with traditional lube & powder coated bullets by swaging my own bullets with the same shape/design for the 35cal's, 44cal's and 30cal's.

In every test the powder coated bullets had the highest velocities. Followed by traditional cast/lubed lead bullets and then jacketed.

My own exp as well, but by coating you remove the mythical lubrication of lead. Again, review the Barnes data, slicker bullets need more powder to achieve the same pressure/vel levels. Only pressure testing would prove it either way.

 

[Biggfoot44]

Bringing plain vs moly rifle bullets into this add pears and tangerines to the apples vs oranges in handguns.

Digging into info back when molly was new , the slickness of molly created issues with bullet pull ( aka effective case neck tension) in magnum revolvers.

Cast bullets can have multiple variables in themselves , but if we stipulate that the hardness and sizing is reasonably suitable for the gun and load in question, the reduced bore friction will make a difference.either higher vel at same pressure , or same vels at lower pressure.

 

[papajohn428]

if the bullet was slicker, vel would be less. You see this in moly coated bullets, less vel with identical charge wts. I believe it is the softer alloy creating higher friction thru greater bore seal, higher pressure & then higher vel. More maleable yes, but slicker, not really.

This makes no sense to me.......a slicker projectile HAS to be faster from decreased resistance. Resistance does NOT increase velocity by raising pressures!

I don't have the Barnes manual, but it sounds like ballistic hokum from here. Maybe moly is a law unto itself, but you'll never convince me that a powder's burn rate and pressure curve is determined by what coating is on the bullet.

It might affect it to a small degree, but it doesn't control it.

 

[Calliope]

Well they are faster than jacketed, hence my theory it is a better bore seal increasing pressures.

If by 'they' you mean plated, they test the slowest of all bullet types according to these tests in auto pistols.
How Fast is your Bullet?

OTOH, this article about moly seems to agree with your side.
http://www.midwayusa.com/general.mvc/index/appcharts~moly-faq

Maybe it's more complicated than I think.

 

[S&WIowegan]

I totally appreciate papajohn's struggle with the idea that moly-coated bullets show decreased velocity, assuming all other factors are constant. It boggled my mind too when a friend and I first discovered it back in the 90's.

We were very active in USPSA shooting and experimented with moly-coated cast bullets from the Bull-X company(RIP). We loaded the same bullets(cast/lubed vs. moly-coated) from Bull-X with identical components and powder charges, brass, primers and fired them over chronographs. We used at least two different chronos to make sure the readings were similar. We ended up totally convinced the moly bullets went slower. Since that meant we had to use more powder to make major we gave up on moly. Moly residue in a gun barrel attracts moisture and the disulfide causes rust. We learned that when we found rust running out of gun barrels left uncleaned.

 

[Forrest r]

Moly coated bullets and powder coated bullets are light years apart, like not in the same zip-code.

They shouldn't even be in the same sentence when comparing bullets!!!!

It doesn't matter if the powder coated bullet is left a soft alloy, or water dropped to harden them or heat treated and aged to harden them.

They have the highest velocity across the board.

It doesn't matter if the copper coated bullet is left a soft alloy, or water dropped to harden them or heat treated and aged to harden them.

They will always be slower than traditional lead/lubed bullets and pc'd bullets.

Moly does what it is designed to do, prevent parts (bbl/bullet) from sticking/seizing together. Hence no seal ='s gas leak or lower pressure due to the lack of a bbl/bullet fit/seal.

Powder coating on the other hand was never designed as a lubricant, it was designed as a protective coating. It just happens to do an excellent job as a bullet lube.

Barnes isn't the "holy grail" or the last word on bullets and bullet lubes. And actually quoting 10+ year old data from them does nothing for modern tests, bullets, lubes or bullet coatings.

1000's of shooters have done tests and keep coming up with the same results. Lead lubricates better than copper and pc lubricates better than traditional lubes/lead.

 

[Steve C]

Both copper jacket and lead seal the bore as well so the pressure will be very similar.

Lead bullets have less "pull" resistance in the bore, hence the higher velocity for the same pressure. Lead bullets are lubed so that the bullet has a lubricant between the lead metal of the bullet and the steel bore to minimize lead contact. No lubricant and you get lots of lead depositing in the barrel.

 

[BlueOvalBandit]

Lead most certainly does NOT lubricate better than copper
Coefficients Of Friction

Dynamic friction/sliding friction is what we care about.

Lead on steel = 1.4

Copper on steel = 0.8

We know powder requires pressure to burn, more friction = different pressure curve, which can mean better combustion of powder. Take a look a max loads, lead will often hit the max pressure before a jacketed bullet of the same weight.

If you've chrono'd coated (be it moly, tungsten, or boron) rifle bullets you'd see a very noticeable drop in velocity just from coating. How do we explain that? Change in pressure curves = changes in the powder burn efficiency.

 

[fredj338]

This makes no sense to me.......a slicker projectile HAS to be faster from decreased resistance. Resistance does NOT increase velocity by raising pressures!

I don't have the Barnes manual, but it sounds like ballistic hokum from here. Maybe moly is a law unto itself, but you'll never convince me that a powder's burn rate and pressure curve is determined by what coating is on the bullet.

It might affect it to a small degree, but it doesn't control it.

Think of it this way. Powder burns & creates pressure to push the bullet. Reduce the pressure generally reduces the vel, all things being eq in the load. Again jacketed moly shows a reduction in vel. Moly coated lead shows a slight reduction or no loss of vel for identical loads. Look at it mother way. Shoot an undersized bullet, friction is less but so is pressure & vel. Just food for thought, but doing a bit of study, a slicker bullet is rarely faster in the bore. My theory, believe It or not, don care, it is my theory. At least i offer a vlid explanation, not just hyperbole. Someday I will have the pressure trace to prove or disprove.

 

[Calliope]

Good stuff, learned a lot.
I guess I always assumed lead was slicker than copper.

 

[fredj338]

Good stuff, learned a lot.
I guess I always assumed lead was slicker than copper.

More malleable, not slicker. Many assume because you can more easily drive one thru a bbl with a rod that it is slicker, but it is just more malleable.