9mm vs .45 ACP vs .40 S&W — Which Caliber Should I Choose?
For most shooters, 9mm is the best all-around choice. It offers the highest capacity, lowest recoil, cheapest practice ammo, and with modern hollow point ammunition, terminal performance nearly identical to .45 ACP and .40 S&W. The .45 ACP makes the biggest hole and has a loyal following but holds fewer rounds and costs more. The .40 S&W is a compromise that is falling out of favor — most agencies that adopted it have switched back to 9mm.
Why It Matters
Your caliber choice affects capacity (how many rounds your gun holds), recoil (how fast you can make accurate follow-up shots), ammunition cost (how much you can afford to practice), and terminal performance (how effectively each round stops a threat). Modern bullet technology has largely closed the gap between calibers, making the choice more about practical factors than raw stopping power.
Compare prices across all three calibers — find the best deals on practice and defensive ammo.
Shop 9mm, .45 ACP & .40 S&W Ammo at Lucky Gunner →The Detail
9mm Luger:
- Magazine capacity: 15 to 17 rounds (full-size), 10 to 15 (compact)
- Recoil: lightest of the three
- Cost: $0.22 to $0.30/rd for practice, $0.75 to $1.50 for defense
- Terminal performance: modern 124gr and 147gr HST/Gold Dot expand to 0.55 to 0.65 inches
- FBI penetration: 14 to 16 inches
- Used by: FBI, most US law enforcement, US military (M17/M18)
- Best for: most shooters, concealed carry, home defense, competition
.45 ACP:
- Magazine capacity: 7 to 8 rounds (1911), 10 to 13 (modern double-stack)
- Recoil: heavier push, slower follow-up shots
- Cost: $0.35 to $0.50/rd for practice, $1.00 to $2.00 for defense
- Terminal performance: 230gr HST expands to 0.85 to 0.95 inches
- FBI penetration: 13 to 15 inches
- Advantages: naturally subsonic (excellent suppressor host), largest wound channel
- Best for: suppressed shooting, 1911 enthusiasts, shooters who prefer heavier recoil impulse
.40 S&W:
- Magazine capacity: 13 to 15 rounds (full-size)
- Recoil: snappiest of the three (sharp, fast recoil pulse)
- Cost: $0.30 to $0.40/rd for practice
- Terminal performance: between 9mm and .45 ACP
- History: developed for FBI after 1986 Miami shootout, widely adopted by LE in 1990s-2000s
- Status: declining popularity, most agencies returning to 9mm
- Best for: shooters who already own one and shoot it well
The FBI's 2014 study concluded that modern 9mm ammunition provides terminal performance comparable to .40 S&W and .45 ACP, while allowing higher capacity, faster follow-up shots, and more affordable training. This led to the FBI's return to 9mm and a wave of law enforcement agencies following suit.
Build Impact
If you are buying your first defensive pistol, choose 9mm. You will practice more because ammo is cheaper, you will shoot more accurately because recoil is lighter, and you will carry more rounds. If you already shoot .45 ACP or .40 S&W well and own the platform, there is no reason to switch — all three calibers work with quality ammunition. Your ability to put rounds on target matters far more than caliber selection.