Representative Boggs.

Just the way you are holding the revolver now?

Mr. Cunningham.

Yes, sir; just the way I am holding it now.

Representative Boggs.

With the cylinder removed?

Mr. Cunningham.

With the cylinder removed.

Mr. Eisenberg.

Now, there is a cylindrical-shaped object in the center of that picture, Mr. Cunningham. Could you describe what that is--right in the center of the picture?

Mr. Cunningham.

That is known by two different names. It is known as a hammer-nose bushing, or a recoil block. It is--Smith and Wesson presses this particular block in. It forms the hole through which the firing pin comes out of the breech face.

Mr. Eisenberg.

That is, the firing pin strikes the center of the cartridge, or the primer, as it is called?

Mr. Cunningham.

Yes.

Mr. Eisenberg.

Which causes the cartridge to fire. Now, what is the magnification of the photograph of the breech face?

Mr. Cunningham.

Of the breech face, it is approximately 17 times.

Mr. Eisenberg.

There are a number of markings or lines on this breech face. Are these the microscopic characteristics which reproduce on the cartridge cases?

Mr. Cunningham.

That is correct.

Mr. Eisenberg.

And are the microscopic characteristics of this breech face individual to this weapon, to the exclusion of all other weapons?

Mr. Cunningham.

They are.

Mr. Eisenberg.

This is your method of determining that a given cartridge case has been fired from a given weapon?

Mr. Cunningham.

The breech face marks, as well as the individual imperfections in the firing pin.

Representative Boggs.

Let me ask a very elementary question, the answer to which I used to know years ago, but I have forgotten. Just exactly what does the firing pin do? What happens after that strikes?

Mr. Cunningham.

Well, it is easier to start with the cartridge itself. The components of a cartridge are a bullet, a cartridge case, a primer in the base of the cartridge case, and powder.
Now, the primer is made out of a very soft metal that can be dented. These primers at manufacture are filled with, basically, an explosive. For instance, Remington-Peters cartridges have PETN, which is one of Du Pont's explosives. RDX is used as one of the components of Western cartridge cases, as well as lead styphnate, lead azides, and other explosive materials.
When the firing pin strikes, there is a small explosion. Fire is given--

Representative Boggs.

How does that bring about the explosion?

Mr. Cunningham.

It is sensitive to detonation by a sharp blow.

Mr. Eisenberg.

That is, the primer is sensitive?

Mr. Cunningham.

Yes; it is an explosive. To differentiate from the powder, which is not explosive. Powder burns.

Mr. Eisenberg.

Now, I have taken Commission Exhibit No. 591, which consists of an unfired cartridge, and there is a round circle in the middle of the base of that cartridge. Is that the primer?

Mr. Cunningham.

Yes. That is actually a separate entity that has been pressed into a hole in the base of the cartridge case.

Mr. Eisenberg.

And that is more sensitive to shock than the powder in the cartridge case itself?

Mr. Cunningham.

Yes. Powder is relatively insensitive. You don't set off powder by a blow.

Mr. Eisenberg.

But the primer is quite sensitive?

Mr. Cunningham.

That is normally. I am talking about a normal blow. The primer is very sensitive. I just named a few of the components, but there are many other compounds in priming mixtures, which are considered secret by each company. But I know that they are explosive mixtures. And the actual striking of the firing pin--with enough force causes a small detonation to occur. The fire given off, goes through holes in the base, and into where the powder is, and starts the powder burning. It is the gases that are given off when powder