Lead Bullets- How They Work

[TBF]

This thread was lost in conversion... Restarting.

The urban legend of leading has it that hard bullets lead less. That is about half the

story.

In the real world there are actually two kinds of leading. Leading from bullets being too

soft and pushed too hard, seen as streaks of lead in the rifling usually toward the muzzle.

And leading from bullets being too hard and not not pushed hard enough, seen as lumpy,

chunky and irregular buildup right outside the chamber. ( forcing cone in revos )

The latter type, caused by bullets that are too hard for the given load, is often diagnosed

as just plain " leading" without regard to it's actual nature. All leading is not the same.

The word " leading " is known to all, but I am constantly surprised by the number of

reloaders who have no knowledge of which type of leading they are experiencing, or it's

origin.

Hard bullet + light load = leading right outside the chamber ( forcing cone on revos )

Seen as lumpy, irregular deposits.

Soft bullet + heavy load = leading in rifling, more toward muzzle.

Seen as streaks.

I thought this might start some interesting discussion, feel free to add your experience

with lead and leading.

Travis F.

[kaiserb]

This sounds quite interesting do you have any formulas for Hardness vs Velocity for leading minimization?

[TBF]

Kaiser,

Nothing concrete, But cowboy action crowd seems happy with BHN 12. Rifle shooters tend

use the hardest they can find, BHN 20+.

My experience is that commercially available lead bullets tend to run toward the hard end

of the spectrum. I have no scientific method of determining this, I use thumbnail or

hammer method.

Most commercial bullets work well in 357 with healty loads of 2400. The same bullet over

2.5gr. Bullseye will lead forcing cone to extreme.

45acp bullets are for the most part too damn hard for any sane load.

The question I would most like answered is: Do lasercast bullets behave the same as

standard lead /tin /antimony bullets, or does the addition of silver to the alloy change

the "stickiness" of the lead? Travis F.

[Duane Thomas]

So, does it? Since I can put 5,000 Laser Cast 200-gr. LSWCs through my .45 with zero leading, I have to believe they're doing something right.

[GRW]

One problem in Cowboy action shooting was the older colt single actions and clones tend to have a barrel diameter which were greater than the cylinder bore diameter. There was a theory that harder alloy bullets would not upset enough to form a seal against the barrel. This caused hot gasses to rush by the bullet causing gas cutting, which would leave lead deposits. You could actually see evidence of gas cutting, or what was perceived evidence, on recovered bullet bases. Since pressure needed to be kept rather low, a solution was to use a softer alloy which would upset under lower pressure and seal the barrel.

[Ironman]

I used Hard Cast bullets in my 45 and got lots of build up just as TBF described. Thinking that I was loading too hot I kept working the load down. The leading got worse. I then started using plated bullets because it would take forever to clean my 1911.

Duane

I would like to know what load you are using with your lead bullets and if you know what velocity they are moving at.

Jim

[Duane Thomas]

4.7-gr. Titegroup, OAL 1.250". Chronos almost exactly 850 fps.

[George D]

When this topic appeared on the previous forum format I was somewhat sceptical about the theory. I use both hardcast commercial projectiles with a teflon coating, which don't have a leading problem at any speed, and my own cast lead projectiles which I use at lower velocites.

At the lower velocities the softer lead gives better accuracy. I have found that the hardcast accuracy at low velocities is mediocre but improves as the velocity rises.

What is the theory behind why a hardcast projectile should lead the forcing cone of a revolver at lower velocity when a softcast does not??

[cukrus]

kaiserb, the formula I have is for hardness vs pressure not hardness vs velocity: minimum pressure (psi) for obduration = brinnel hardness x 480 x 3; the maximum pressure to avoid leading = brinnell hardness x 480 x 4.

George D, the hardcast bullet does not obdurate at lower chamber pressure while the softcast does; expect the leading near the chamber with the hard cast. At higher chamber pressure the hardcast will obdurate and not lead but the softcast will lead - expect the leading toward the muzzle.

E.g. A bullet with a bh of 12 would have a calculated minimum chamber pressure of 17 280 psi for obduration and a max chamber pressure of 23 040 psi to avoid distal leading. A bullet with a bh of 22 would have min ad max chamber pressures of 31 680 psi and 42 240 psi (respectively.)

Now where did I get this?

cukrus

[George D]

Bear with me here guys. I understand the symptoms of this phenomena but am struggling with the cause.

Traditionally more powder=more pressure=more velocity and more heat. Softer projectiles have a lower melting point and therefore produce leading at a lower level. A harder projectile will have a higher melting point and should not produce leading at low velocities due to melting, but may be sufficiently unyielding, or obdurate, as to engage the rifling less that a softer projectile and produce inferior accuracy. But why would it produce leading at low velocities? Is the theory that the slow hard projectile skids over the rifling rather than engaging it, thus ripping off some lead??

[dajarrel]

Hey guys,

I'm a new guy to this forum and have been fighting leading in various calibers for years. I believe you can push a bullet too hard and cause lead to "strip off" and leave lead in the grooves. I have also found that a bullet that won't obscurate (swell or bump up) when fired will let gas get by the bullet and "melt" off lead and cause leading.

But the one thing that I found that reduced and almost eliminated my leading is making sure that the bullet diameter is at least .001" greater than the bore. For example in a .40S&W, the bore diameter is .400". If you size your bullets to .400" it will let gas leak by, but if you size to .401", in my experience, almost all the leading stops. The same applies to my .357 revolver: .357"=leading, .358" greatly reduced leading. Alot of really hard core accuracy shooters will recommend "slugging" your barrel by pushing a soft lead slug down it and then measuring the actual barrel diameter, groove to groove, and adding .001" to that measurement.

Dennis

[Duane Thomas]

In the Laser Cast load manual, they state that in their tests, their bullets fully obdurated at as low as 10,000 psi. I have to wonder if the tested lower than that. According to the Hodgdon load manual, the Titegroup load I'm using gives Major pf with circa 7,000 psi.

[cukrus]

George D., pure soft lead has a higher melting point than hard linotype and other lead alloys. Leading with a hard alloy is thought to be due to "gas cutting" as it blows past the bullet. Obduration was the term used by the source of the formula I quoted, but the correct term may be obturation or sealing of the bore by the bullet. As noted above a larger bullet may be used to do that, and the lube used may act as an "O" ring as well.

cukrus

[George D]

cukras,

Thanks for the info. You're right, the word is obturation. I found a little bit of history on the subject at :

http://riv.co.nz/rnza/hist/art77b.htm

There is always something new to be learned on this forum. I'll have to do a bit of reading on lead alloys.

[kaiserb]

I have had pretty good luck with Kead bullets on top of tite group. They do not seem to lead the barrel or the forcing cone at all. Keads are used a lot by the Cowboy Action folks, although they seem quite hard.

[TBF]

George D,

Skepticizm is good.

Try this:

357, shoot same bullets over healthy charge of 2400

shoot same bullets over 2.5gr. Bullseye

Clean between.

Observe leading.

But that does not adress the cause of the symptom, I can only give an unscientific

guesstimation.

Imagine the base of the bullet being either firmly conforming to the

bore when obturated, and having no exposed 90 degree edge.

When not fully obturated the edge is slightly away from the bore. If you have ever

seen the inside of an engine which has gone thermal, you see all the sharp edges of pistons, etc. have melted. Running a gasoline engine on kerosene will really show this, but that is another story entirely.

I believe the leading by hard bullets with light loads is deposited in molten form,

this would account for its lumpy irregular appearance.

Travis F.

[George D]

Hi Travis,

Thanks for your explanation on the cause of leading in hard projectiles.

Some years ago I used to cast my own projectiles for 38/357 revolvers. The accuracy formula was to size the projectile .005 above the cylinder throats to prevent the leaking of searing hot gases along the side that you describe. An accurate revolver would have a barrel diameter just in front of the forcing cone of .005 less than the cylinder throat diameter and decrease by another .005 at the muzzle. When casting projectiles the compostion of the alloy determines the cast diameter. The harder the alloy, the larger diameter, so a wheel weight alloy would cast .357 and a Lyman #2 would cast .358 from the same mould, the point being that a hard projectile is likely to be a larger diameter than a soft.

If you fire a 358 dia projectile into a 357 dia barrel (rifling dia), what else can it do but fill the rifling? I have read the searing gas theory before but it has related to projectile diameter rather than Brinell hardness.

I don't doubt the results of your experiments, but I'm still grappling with possible causes. I guess this is one of the downsides of an INTP personality type.

[TBF]

George,

Like I said it's just a guess at the cause, the result can be known for sure.

You might start a thread sometime on the sizing thing, I am sure it would be interesting.

My experience with casting/sizing is nil. My check for sizing is about as unscientific as my

lead hardness test, drop a bullet into cyl. , if it falls through it is too small, if you can't

punch it through with "about the right feel " (using a wooden dowel) it is too large.

Using store bought bullets, most are fine, but if they fall through you have most likely

got a loose cyl. YMMV but most commercial bullets are pretty close to 358 for 357.

Semi shooters can slug the bore, but I never have. Semis are also much more difficult

to observe real traditional bore leading in, most bullets are way too hard. Leading right

outside the case is much more common in my experience.

Travis F.