Cal 30 Light Rifle Observing

I have a Cal 30 Light Rifle cartridge, photo follows, that I have cataloged as a T103E1 Observing. It is headstamped FA 51.

There is also a Cal 30 cartridge, the T99, that is loaded with what appears to be the same bullet and same headstamp.

On another thread re: color tips, there is a cartridge with what appears to be the same yellow tip ID’d as a “fumer”. It is headstamped FA 71

I have only single specemins so I cannot pull the bullet to see what’s inside. So I’m asking,

What exactly is “Observing” and what does the bullet consist of?

What is a “fumer” and what does the bullet consist of?

Are they the same cartridge?


“Observing” is likely the designation for a B-Patrone-type spotting round, one that traces to the target then explodes on impact; is it possible you could have it X-rayed?


That would be my guess also. No way to x-ray. What does the spotting round bullet consist of?

Anyone have an idea of what a “fumer” is?


“fumo” in italian is “smoke” .The root of the word is the same,so they can have similar meaning

I have no idea what a fumer is other than to guess it perhaps leaves a smoke trail.

However,observing rounds usually have a tip filler that flashes or gives a puff of smoke on impact. They do not normally trace. The German B-patrone and similar have an internal detonator to produce the flash, whilst others, like the British .303 O Mark I, have a chemical filling in the tip to give the flash/smoke on impact.

I would expect the .30 light rifle observing round to have the latter type of tip filler, but I do not know for certain.



The T103 observation rounds were designed to give a puff of smoke on impact. The construction is quite complicated - Brandt et al. show a sectioned round in their book on 7.62 NATO cartridges. The bullets most likely contain a sealed pellet of white phosphorous to provide the smoke. If you gently shake genuine cartridges, you can hear the striker mechanism rattle.
The T103 used a FAT1 case (49mm in length) and a modified .30 cal T99 bullet. The T103E1 used the full length case.

Left to right
T103 HS F A 48 * Br cs Ni pr
T103E1 HS F A 51 Br cs and pr, Green PA
Fumer HS (+) FA 71 Br cs and pr, Red PA

X-ray of T103

X-ray of T103E1

T103E1 box (unfortunately opened)

The yellow tipped round described as a fumer is clearly a tracer of some type but very different to the T103E1 - see x-ray (may not be clear in the posted images). The bullet has GMCS jacket and clear tracer compartment at the base, followed by an X-ray opaque core and finally a second compartment in the tip which is not x-ray opaque.

Top - Fumer, bottom T103E1

Dave Hughes in his book on the M16 and its cartridges gives some detail on the fumer effect. He states “A fumer is a method of reducing the base drag of a projectile by injecting the proper amount of heat and mass into the projectile bas region during flight. This could be thought of as somewhat analogous to tracer ammunition as the tracer material is burned in the base area. However, the fumer doesn’t have a luminosity requirement.” As to whether the yellow tipped “tracer” cartridge does not trace or leaves a smoke trace as has been suggested, I don’t have an answer at present.



Thanks for all that. I knew you’d have the answer but didn’t want to ask directly. That way it keeps the Forum guys interested.

I see that the “fumer” cartridge has the 10 ogive bullet. I’m guessing that is the best way to tell them apart? And the date of course.