Walk into any gun store and you'll face an entire wall of ammunition options. Same caliber, dozens of SKUs, prices ranging from 15 cents to $2 per round. The marketing language — 'Critical Defense', 'Defender', 'Gold Dot', 'HST' — tells you almost nothing useful.
Here's the framework that makes it simple: two purposes, two ammo types. Training ammo is cheap, range-friendly full metal jacket (FMJ). Defensive ammo is hollowpoint, reliably expands on impact, and lives in your gun for actual use. The rest is details.
FMJ vs. Hollowpoint: The Core Distinction
Full Metal Jacket (FMJ) — also called ball ammunition — has a lead core fully enclosed in a copper or brass jacket. The bullet does not expand on impact. It maintains its shape, penetrates deeply, and exits the target. FMJ is cheap to manufacture ($0.15–$0.35/round for 9mm in 2026), reliable in virtually all firearms, and produces consistent performance. Use it for all training and range sessions.
Hollowpoint (HP) ammunition has a cavity in the nose. On impact with soft tissue, hydraulic pressure causes the bullet to expand, mushrooming to 1.5–2x its original diameter. This expansion transfers energy more efficiently to the target, increases the wound channel, and slows the bullet — significantly reducing the risk of overpenetration through walls. Quality hollowpoints cost $0.50–$1.50/round. Keep them loaded in your defensive firearm.
The reason you don't train with hollowpoints is purely economic — running 500 rounds of Federal HST at $1/round for a training session is $500 vs. $75 with FMJ. Your skill development is identical. Train with FMJ, carry hollowpoints.
What 'Grain' Means and Why It Matters
Grain (abbreviated 'gr') is a unit of weight — 1 grain = 0.0648 grams. For a given caliber, heavier bullets (more grains) travel slower but carry more momentum. Lighter bullets travel faster but have less mass. The tradeoff is terminal performance vs. recoil and trajectory.
For most new gun owners: buy 124 gr FMJ for training and 124 gr hollowpoint (Federal HST, Speer Gold Dot, or Hornady Critical Duty) for carry. That's it. The nuance between 115 and 124 matters far less than practicing regularly.
Best Defensive Ammo by Caliber (2026)
These recommendations are based on FBI ballistic testing protocols, law enforcement adoption, and documented real-world terminal performance:
9mm Luger — Federal HST 124gr ($32/50): The benchmark. Consistent mushroom, reliable expansion through common barriers (auto glass, denim, drywall). Used by the FBI and most major metro police departments. Also excellent: Speer Gold Dot 124gr ($30/50), Hornady Critical Duty 135gr.
.40 S&W — Speer Gold Dot 180gr ($36/50): Largely being phased out by agencies moving back to 9mm. If you have a .40, Gold Dot or Federal HST 180gr are your best options.
.45 ACP — Federal HST 230gr Standard Pressure ($38/50): At the caliber's natural pressure, HST expands reliably and achieves excellent FBI test results without the increased recoil of +P loads.
.380 ACP — Hornady Critical Defense 90gr ($28/25): The .380 is the most performance-sensitive caliber — bullet design matters enormously. Critical Defense and Speer Gold Dot Short Barrel are the only two options I'd recommend in this caliber.
Where to Buy Ammo and How to Stop Overpaying
The gun store counter is the most expensive place to buy ammo. You're paying for convenience and immediate availability. During normal supply conditions, use these sources instead:
Bulk online retailers — Ammoseek.com aggregates pricing from all major online retailers in real time. For 9mm FMJ (training ammo), you should be paying $0.15–$0.22/round in 2026 bought in 500–1,000 round cases from Lucky Gunner, Ammo.com, SGAmmo, or Sportsman's Guide.
Big box stores — Walmart, Cabela's, Bass Pro, Academy Sports. Often the best local price, especially on .22 LR and bulk pistol ammo. Prices reset weekly.
Gun shows — Inconsistent. Can be excellent deals or 50% over market. Know Ammoseek prices before you go.
Storage: buy in bulk when prices are low. 9mm FMJ has a shelf life measured in decades when stored in a temperature-controlled environment with low humidity. A 1,000-round case costs the same per round as 50-round boxes and removes the logistics of frequent small purchases.
For defensive ammo specifically: buy two boxes (100 rounds) — run 50 rounds through your specific gun to confirm reliability, keep 50 rounds loaded and in reserve. Replace annually if unused.
DJ Cavalcanti is the founder of DownRange, America's Firearms Intelligence Hub. A lifelong 2A advocate and Washington State resident, he built DownRange to give every American gun owner access to the legal intelligence and practical knowledge they need — all in one place.