Speer TMJ™ 357 Sig - 357 SIG/38 Super TMJ FN Bullet. THE ULTIMATE FMJ BULLET. Speer™ uses Uni-Cor™ technology to take full metal jacket bullets to their highest level of evolution. They completely encase the lead core in a seamless jacket. Other FMJ bullets have lead exposed at the base, or have an accuracy-robbing second piece to cover the lead. Those bases can deform under pressure. TMJ’s seamless jacket means this can’t happen. Airborne lead goes down, and TMJs won’t foul ported recoil compensators like open-base bullets do. They swage each bullet twice, ensuring consistent diameters and a uniform heel. TMJ™ bullets are great for casual practice and plinking because, in addition to being super-accurate, they are economical.