- TMJ Or Total Metal Jacked
Stands for Total Metal Jacketed, a term used by Speer to describe the full-metal-jacketed bullets in which even the base is jacketed. Total metal jacket bullets, often referred to simply as "TMJ", are the most widely used bullet type at indoor ranges and among competitive shooters. The reason for this is a simple one but important: The normal full metal jacket or FMJ bullet has a small amount of exposed lead at the base of the bullet while the TMJ does not. The TMJ surrounds the otherwise exposed lead area with copper.
FMJ on the LEFT vs TMJ on the RIGHT