Sintered Bullets


#1

Speaking of sintered bullets, does anyone know of a fool-proof way that a fool such as me can tell one from the others?

Ray


#2

Ummmm, you’ve lost me on this one Ray!


#3

Jim

Sintering is a method used to create objects from powders. Pressed in a mold. I know that Frankford Arsenal (and probably others) experimented with sintered bullets in several calibers. The bullets could be plated, washed, clad, or left plain.

Ray


#4

I expect it’s just me missing something Ray…but who was talking about sintered bullets?


#5

Jim

Oh, now I see where you were going. I’m not the brightest light on the Christmas Tree, at times.

That’s my way, tongue-in-cheek, of introducing a new subject.

Ray


#6

Actually, I was talking about a .45 supposedly with a sintered iron bullet, that I could not verify as such, on the current thread dealing with U.S. steel-case .45 ammo from the 1940s. I feel like chopped liver here. :-)


#7

Ah, right! Thanks John, makes sense now. I wasn’t actually following that thread…but if you fancy chopped liver you go right ahead, great with onions!


#8

I was shooting in an indoor gun range the other day and the owner only allowed “Green” ammo to be used that was lead free in every way. We shot 45’s, 9’s, and 380’s all with what I think were fitted with sintered projectiles. Some looked like super compressed copper dust? It was interesting because some of the 9MM rounds had projectile failures where after firing one bullet, two holes punctured the target. The funny thing is that both holes on the targets were perfectly round like a wadcutter hit the paper. We were firing from 30 feet away and both holes were about 6 to 8 inches apart. Some projectiles actually broke at the case mouth while loading into the clips.

Jason


#9

Ray,

Actually, someone was discussing sintering: Me, in my Gyrojet book (shameless plug). Some 12mm and 13mm Gyrojet rocket nozzles (bases) were made by MBA by compressing powdered electrolytic iron having between 20% and 50% carbon. The powdered iron was compressed under extremely high pressure in a mold, and the finished piece had exactly the right dimensions and finish with no machining or trimming required.

Then, a batch of the pieces were sintered, which means that they were heated in a furnace to a temperature just barely under their melting point and then allowed to cool. This sintering process caused the iron particles squeezed closely together in the mold to form into a single mass.

There was almost no waste in the powder metal technology, and the pieces formed by it were extremely precise and uniform piece to piece. Most bullets are, of course, not a single mass of something but are layers of different metals with a core.

You can recognize a powder-metal/sintered piece under magnification by its slightly rough-appearing surface, sort of like a sponge.

Mel


#10

Thanks Jason and Mel. I was thinking about sintered bullets made and tested by Frankford Arsenal, but your posts made me aware that there are more modern uses for sintered bullets and parts, probably more so than the few experiments that FA did.

Good stuff.

Ray


#11

Sintered bullets, usually of copper, are offered now by a few manufacturers and are intended primarily for training, although they also have some use in short-range urban action where you don’t want barrier penetration or ricochets.

Another use is in door breaching, for which 12 gauge sintered slugs are the current fashion. These can blow off locks or hinges then instantly turn to dust so won’t injure anyone in the room behind.


#12

I’ve been involved somewhat in sintered bullet manufacture in the past. There are several different technologies that can be used, and most any metal that can be powdered can be sintered, and in fact “alloys” can be made by sintering combinations of metal powders pressed together. Also, mixtures of high- and low-melting point metal powders can be combined and sintered, such as copper and tin, wherein the tin melts and effectively solders the copper particles together. This is called liquid-phase sintering. The sintering temperature used in solid-phase sintering is considerably below the melting point of the metal used. The metal particles in solid-phase sintering are not melted together, but are attached to each other by what is essentially a type of atomic-level chemical bond induced by pressure and heat. A commonly-used example is letting a bowl of ice cubes sit in your freezer for awhile. After some period of time they will stick together, but there is no melting involved.

Some poorly manufactured sintered bullets can indeed come apart in the barrel, but those made by Sinterfire (of copper) and by some others work very well, at least in handgun loads. In my experience, they tend to break up more frequently when used in rifle loads, but there may have been some product improvements made by now. They tend to be not as accurate as lead or jacketed lead bullets, and are of lower density than lead, but in most cases they are completely satisfactory for training use. They are frangible and break up into a fine powder upon impact with a hard surface, and will not ricochet. That, and also because they do not contain lead, makes sintered bullets desirable for use at indoor ranges.


#13

A sintered product enjoyed by engineers since the 1930’s is “Oilite” which found its way to ammunition technology quickly after its development. This oil impregnated sintered bronze makes for a wonderful bearing material.

Here is the classic WWII era civilian reloaded product by Dairt featuring this type of projectile. At a quick glance it would seem to be a typical copper jacketed or plated bullet. Its low density weight of about 146 grains in this .45 ACP loading is a good clue that there’s something different about it.

Anyone have some US military experimentals using this material that they might tell of or show?

Dave


#14

Another “combined” material in use now, e.g. by RUAG in their “Copper-Matrix” frangible bullets, is a mixture of copper powder and polymer.


#15

Correct. Polymer-matrix copper is in common use for frangible bullets. As I previously discussed the core of the Cesaroni frangible bullet used in the AA40 5.56 frangible round is copper powder in a nylon matrix. One trick is the use of graded copper particles (sized so that small particles fill in the voids between larger particles) to obtain a higher density. These frangible bullets don’t actually fit the definition of being sintered, but in a way are somewhat analogous to liquid-phase sintering. The weight percentage of the polymer in frangible bullets is very low.

The earliest Cesaroni bullet cores used a different polymer matrix (Surlyn) that proved unsatisfactory, resulting in bullet breakup in flight under some conditions.

The main problem with using copper as a frangible bullet component is economic. At one time tungsten powder was incorporated with copper powder in the manufacture of plastic-matrix bullets in order to increase bullet weight, but this had two disadvantages - even worse economics and also environmental problems. The U. S. Army found out about that the hard way.


#16

This turned out to be a lot more than what I intended. But, thanks to all who have posted.

So, can I assume there is no 100% way to tell if a cartridge is loaded with a sintered bullet, other than possibly the weight?

Ray


#17

You can hit it with a hammer to see if it breaks. Actually, sintered bullets have a little lower density than a solid copper bullet of the same dimensions due to porosity, and much lower than a lead bullet’s. So you could determine the specific gravity of the bullet and compare it to copper’s or lead’s. I won’t explain how this is done, but if you really want to know, PM me. It’s fairly simple if you have a sensitive balance. Also, you would probably be able to see a difference in the surface appearance under a microscope or high-powered magnifier.


#18

The Germans loaded a lot of 9mm Para with a sinterered bullet during WW2. Probably Lew can write a book about it.
They were also made at the end of WW2 in 8 x 33 (Stg 44 ) and some 8mm Mauser.

At the label you read “SE” Sinter Eissen.

Rgds
Dutch


#19

Eureka! ;-)


#20

A variety of sintered bullets were produced by or for the Special Operations Division of the Bio weapons section at Ft. Detrick prior to 1970. These were produced with a variety of bio test simulants to determine the possibility of attack using pistol caliber weapons. Some of these were done in .45 auto.