nothing

different manufacturers use different vocabulary. I find it annoying . . .

 

TMJ is used to indicate that a bullet has a complete jacket, hence Total Metal Jacket. They are often "plated" or "washed" jackets.

FMJ (Full Metal Jacket) bullets usually have an exposed lead core at the base with a jacket that is placed over the lead core, then swaged into the shape of the bullet.

TMJ bullets are thought to smoke less, since there is no lead core exposed at the base which is subjected to extreme temperatures which vaporize the lead base during the very short time frame that the bullet is traveling down the bore.

 

Some ranges are moving towards allowing only TMJ rounds because of lead concerns/health regs. I found this out when I shot at Top Gun in Houston.

 

Interesting... The TMJ cartridges seem often to cost less. Would that be because it costs less to plate or "wash" the bullets?

Is there any performance difference?

 

I don't know that I have noticed in smoke difference between TMJ and FMJ ammo made by the same company. I have only seen 9 mm shot side by side at an indoor range and I saw no difference in the VISIBLE smoke output. No doubt that the lack of an exposed lead core at the base with TMJ ammo precludes the lead in the base from vaporizing into the air. That is a genuine concern.

See this site for some interesting information on jacketing and lead exposure...

http://www.co.ba.md.us/police/academy/html/lead_poisoning.htm

Both TMJ and FMJ will produce a tremendously less amount of smoke than unjacketed lead ammo.

 

When I tried to develop a load that gave zero visible smoke (for USPSA and IDPA match use), I tried exposed lead core and totally encapsulated jacketed bullets and couldn't see an appreciable difference between them.

At that point, I chose to shoot up what I had and then buy whichever FMJ or TMJ bullet that I get the best deal on. The only material difference in emitted smoke was between lead (D&J bullets) and jacketed (W-W FMJ).

I was using V-V N-320 powder in .45 ACP, which is clean burning to begin with. Some of the dirtier powders, like W-W 231 smoked a little more than the V-V, regardless of bullet.

 

RE: The difference

When I tried to develop a load that gave zero visible smoke (for USPSA and IDPA match use), I tried exposed lead core and totally encapsulated jacketed bullets and couldn't see an appreciable difference between them.

At that point, I chose to shoot up what I had and then buy whichever FMJ or TMJ bullet that I get the best deal on. The only material difference in emitted smoke was between lead (D&J bullets) and jacketed (W-W FMJ).

I was using V-V N-320 powder in .45 ACP, which is clean burning to begin with. Some of the dirtier powders, like W-W 231 smoked a little more than the V-V, regardless of bullet.

The difference you saw between the lead and FMJ was mostly the lube used on the lead bullets. I loaded lead bullets at one time for a Thompson SMG but couldnt stand the clouds of smoke it produced with a 30 rnd mag, so I've gone to FMJ exclusively.
Most powders don't smoke too badly compared to bullet lube.

 

Thompsons were meant for FMJ bullets!

 

Senator, I bet that was something to see! I with you regarding the bullet lube. What I was doing was to trying to see if TMJ bullets smoked less than FMJ bullets. When I couldn't find a definable difference, I started trying different powders to see if I could find one that was better than another. Didn't find any huge difference there, but did decide that the V-V powders were maybe better. This was before Hogdon came out with the Tite series of powders.

The purpose in this excercise was to develop a load that you could use in a match course of fire where you could be firing a bunch of rounds really fast in a confined space, when the sunlight was coming from low in the sky and in front of you. I got bit a couple of times by this in IPSC matches and was looking for a cure.