Do you believe that lead boolits actually obturate (swell up) when fired? Yes or No

[Don Sarkisian]

Russell, with all due respect, my friend, I think your mind is made up and I don't think anyone is going to change it for you. Having said that, I don't think labaratory proof would convince you of obturation.

As a new member here let me just throw something out for consideration.For exemple,rubber is a viscoelastic material having both the properties of steel (elastic) and liquid (non-compressable).You can change its shape and its dimension in direction but it will not compress.I believe that lead does not exibit an elastic property nor is it compressable.However,subjected to sufficient force its shape can be changed and therefore its dimension.If that is true then lead bullets under certain conditions will bump up or obturate.Consider firing a revolver or rifle bullet that is undersize for the bore.A power charge that is quite light for caliber will generally result in leading because there insufficient pressure to bump up the bullets diameter to fit the bore.Now increase that powder charge up towards maximum and with that being the only change it should be expected that leading will be eliminated.Why,most likely because the bullet bumped up to bore diameter sealing the bore,stopping gas blowby and holding the rifling unlike the 1st issue.

Whew

[billw]

As a new member here let me just throw something out for consideration.For exemple,rubber is a viscoelastic material having both the properties of steel (elastic) and liquid (non-compressable).You can change its shape and its dimension in direction but it will not compress.I believe that lead does not exibit an elastic property nor is it compressable.However,subjected to sufficient force its shape can be changed and therefore its dimension.If that is true then lead bullets under certain conditions will bump up or obturate.Consider firing a revolver or rifle bullet that is undersize for the bore.A power charge that is quite light for caliber will generally result in leading because there insufficient pressure to bump up the bullets diameter to fit the bore.Now increase that powder charge up towards maximum and with that being the only change it should be expected that leading will be eliminated.Why,most likely because the bullet bumped up to bore diameter sealing the bore,stopping gas blowby and holding the rifling unlike the 1st issue.

Whew

Don and Jim,

Undersized bullets of any alloy or hardness will lead regardless of powder charge as before the pressure reaches its maximum, gas will escape around the bullet. its lube and lead will be gas cut down the bore and very little can be done about subsequent leading. Unfortunately, this is a common problem for everyone with poorly fitted cast bullets unless a custom chamber is cut or the bullet is completely breech-seated ahead of the cartridge as is done by the Single Shot shooters. I don't have any custom chambers or rifles and the only SS rifle I have is an 1884 Trapdoor, same problem with it but I solved that with oversized moulds.

I made some breech seaters with cartridge cases, used them in bolt action rifles and got the tightest groups ever, again wrote an article with photos in the Fouling Shot. Later, Merrill Martin and I worked with some soft vinyl PVC wads and got almost the rest of leading resolved and better match accuracy over long strings.

I attempted to resolve this leading situation many years ago in a TFS article by using granulated Cream of Wheat as a filler, noting new in using fillers. No bullets leaded either from the massive gas check filler or the filler cleaned the bore on each shot. I shot air cooled WW, fully hardened from 450F heat treatment and quenched, some with or without either Hornady GC or lube and the worst was a 30 cal paper patched bullet without a patch, 0.301" diameter in a 308 Win. All loads would have "hunted" at the 50 yd back stop. The most accurate loads were with the fully hardened WW bullets with HGC and lube. MV increased 400 fps over 1600 fps without filler. I used rifle powders and about 28 gr of 4064 and other near burning rates, about a 70% charge of a maximum book load without fillers of course. Pressure had to increase with the added MV. I loaded all rounds at the shooting bench, no case sizing, just new primer, filler and drop a bullet in the neck and fire them. No air space was allowed under the bullets.

In addition, bullet fit is an absolute necessity of the three "B's" in accuracy: bullet, barrel and bedding. When chambered, the bullet nose must contact the lands of the bore in a rifle and if possible, the top driving band should touch the throat for two contacts, easily done in a bolt action, not easily done in semi-auto rifles and handguns. Revolvers need a bullet that is a snug fit in the cylinder throats and most bullets are seated well behind the throats and the best example is the target WC factory loads. Cylinder throats must be slightly larger than the groove of the barrel and the forcing cone must be large enough to compensate any misallignment of the cylinder, a compromise we have with revolvers.

I rarely use fillers unless needed in my 458 Win Mag. Fillers can contaminate powder spaces and should have a card wad between the two. Filler and lead can accumulate at the transition of neck and leade and it must be cleaned out or excess pressure will occur and is dangerous.

Warning!
Fillers can be dangerous and should not be used by new landloaders and utmost caution must be used by experienced handloaders. I have broken one bolt face in a rifle and pierced primers in handguns. Handguns are even more dangerous than using fillers in rifles.

[legi0n]

And that my friends is what brought me to start a poll here.

From my high school and college physics/chemistry classes, there are only four states of matter:

1. gases
2. liquids
3. solids
4. plasma

Also, in those classes, I learned that of the first 3, only the gases are compressible. Liquids are not compressible, and that explains why hydraulic pistons work on something like a crane or a back-hoe. And why they don't use pneumatic rams or pistons for some stuff. Solids aren't compressible, like a block of steel. So my thoughts are that a cylindrical piece of lead is a solid, and therefore can't compress or be compressible. Unless of course it was surrounded all around by something strong like a steel swaging die and pressed into a particular shape.

What I am saying is that with the exception of very soft lead and/or Minie balls, I think lead boolit obturation might just be a myth.

You might want to take a look at the theory of sonics by Gogu Constantinescu which relies on fluid compresibility. http://en.wikipedia.org/wiki/Theory_of_sonics
This guy used his theory to create (among others) a mechanism to sync a machine gun to a plane propeller so that the MG was firing between the propeller blades. Kindof neat!

Soft metals can be thought of as highly viscous fluids. There seems to be some compressibility.

[MT Gianni]

The lead does not compress in the bbl, it enters weighing xx grains and leaves it the same weight- lead left in the bbl. It may change shape as to becoming shorter and wider like it was swedged but that is not related to compression in fluids. Fluids change shape but one cup of oil displaces the same amount of air @ 14.7 psi as it does @ 1470 psi. That shape might be contained in a vessel 4" tall or 14" tall, it displaces the same amount of volume and is not compressed.

[billw]

Boolit Bub and MT Gianni,

I had to assume the paper patch 0.301" diameter bullet without a patch did bump up enough to get enough spin in the 308 Win barrel to shoot as accurately as it did.

I have the Wolf Publishing company reprint of Dr. Mann's text book "The Bullet's Flight" with Harry Pope's notes in the margin. It is a difficult read, a good reference text but I noted his short barrel tests, the last one of about 1" long with bullet nose protruding from the barrel, when shot and bullets recovered with bullet bases expanded well above the original diameter. My interpretation of this phenomenom is possibly due to one or both of the elasticity of a lead bullet still attempting to bump and continues to expand as in a plastic, putty or rubber mass or the gas flow at the muzzle forced the base to expand. More than likely it was due to the putty like characteristic and not the gas flow at the muzzle. Imagine a baloon full of water and slowly bouncing it on a flat surface. It will oscillate from compression but return to round shape after the force is removed. The bullet in Dr. Mann's tests may be behaving in a similar manner except that it would not return to a cylinder shape.

That test may certainly indicate the nature of a bullet bumping up in a bore or trying to bump up even if fully fitted as in a breech seated bullet. In a regular 18+" bore, the gas pressure and bumping effort is relaxed enough that the bullet will no longer attempt to have the base bump larger. But we don't know that for sure do we? That bullets and barrels oscillate like a guitar string is a fact, same as a wire antenna resonating for a radio transmitter or receiver. I would assume a bullet oscillates for the same reason, attempting to bump/obturate at max PSI just in front of the throat of a rifle but is relaxed as pressure is reduced due to the expansion ratio and exit at the muzzle with much less pressure.

Yes there is only very slight comnpressibility of some liquids and metals due to solid matter or voids and very little compressibility in some solids, best to say they are not comrpressable if they are in a pure form with no traces of other elements or compounds.

[KCreload]

If you load a 270 with 25 caliber gas checks on the back, the gasses will go around the the lead and spit the bullet out tumbling. That is a long skinny bullet and it doesn't obturate (linotype/led mix of unknown hardness, but works well normally)
I vote no under that condition.