The single most important rule: the cartridge name on the box must match what's stamped on your barrel or slide, exactly. "Close" is not a match. Before you shop, look at the markings on your gun and confirm them in the owner's manual.

Most mismatches come from names that sound alike or rounds that physically fit where they shouldn't:

Pressure ratings

+P and +P+ loads run hotter than standard pressure for more velocity. Many modern pistols handle +P without issue, but older and lightweight guns may not. Check your manufacturer's guidance. +P+ has no industry standard and is best reserved for firearms specifically rated for it.

Once caliber is settled, bullet construction is the real decision. The same cartridge can be loaded for very different jobs, and the wrong construction will underperform no matter how good the brand.

FMJ deserves a specific note: it's excellent for training and wrong for nearly everything else. It doesn't expand, so it wounds game poorly and tends to over-penetrate in a defensive situation. Many states prohibit it for big-game hunting.

A good defensive load does two things: it expands consistently and it penetrates deep enough to stop a threat without traveling much further. Law enforcement agencies widely use a standard that calls for 12 to 18 inches of penetration in ballistic gelatin, and the major defensive lines are designed around it.

What to look for

• An established defensive line from a major manufacturer, not a novelty design.
• A load tested in barrels close to your own length. Short-barrel versions exist for compact pistols because velocity drops in short barrels and expansion can suffer.
• Recoil you can control for fast, accurate follow-up shots. A load you shoot well beats a hotter load you don't.

Prove it before you carry it

Fire at least a few boxes of the exact load through your gun and magazines. You're looking for zero malfunctions and a point of impact that matches your practice ammo. For cheaper training, pick FMJ in the same bullet weight so the gun shoots to the same point.

Rotate your carry rounds

Repeatedly chambering the same round can push the bullet deeper into the case, raising pressure. Rotate the top round, and retire any cartridge that looks shorter than the others.

Ethical hunting means a clean, quick kill, which depends on enough energy, the right bullet, and a shot you can make. The matrix below is a general starting point for North American game. Your state's minimums always take priority.

Bullet weight within a caliber

Lighter bullets in a given caliber suit smaller game and flatter trajectories. Heavier bullets carry more momentum and penetrate deeper, which matters on elk and bear. For a .30-06, that might mean 150 grain for antelope and 180 grain or heavier for elk.

Lead-free areas

Some states and many federal lands require lead-free ammunition for some or all hunting. Monolithic copper bullets are the usual answer. They tend to shoot well at a slightly lighter weight than the lead-core bullet you're replacing, so check your zero before the season.

Three numbers define a shotshell: gauge, shell length, and shot size. Gauge and length must match your gun. Shot size is your choice, and the smaller the number, the bigger the pellet.

Steel is lighter than lead, so it slows down faster. The rule of thumb is to go about two sizes larger in steel. Tungsten is denser than lead, which is why tiny TSS pellets still hit hard.

Slugs and barrels

Smoothbore barrels pair with traditional Foster-style rifled slugs. Rifled barrels are built for sabot slugs, which are far more accurate at distance from that barrel. Mixing them works but costs you accuracy.

Rimfire ammunition is primed in a ring around the case rim rather than a separate primer. It's inexpensive and low-recoil, which makes .22 LR the most common round for teaching new shooters and taking small game. Rimfire cases can't be reloaded.

.22 LR is sold in several velocity classes. Semi-automatic guns generally cycle best with high-velocity loads. Bolt actions, revolvers, and suppressed guns often get their best accuracy from standard-velocity or subsonic loads. Rimfire guns are known for having preferences, so try a few before buying in bulk.

.22 WMR and .17 HMR are faster, flatter-shooting rimfire cartridges for longer small-game and varmint shots. Neither is interchangeable with .22 LR.

Ammunition has no expiration date. What shortens its life is moisture, heat, and temperature swings. Stored well, it stays reliable for decades.

• Keep it indoors in a climate-controlled space. Garages, attics, and damp basements are the usual culprits.
• Use gasketed ammo cans and drop in a desiccant pack. Recharge or replace the desiccant periodically.
• Keep defensive and hunting ammunition in its original box so the lot number stays with it.
• Lock it away from children and anyone who shouldn't have access.

Inspect before you shoot

Set aside any round with green or white corrosion, dents or cracks in the case, a loose or recessed primer, or a bullet that is pushed in or loose. Don't throw problem ammunition in the trash. Your local range or law enforcement non-emergency line can tell you how to dispose of it.

Ammunition rules vary by state, and they change. Common examples include:

• Federal minimum ages when buying from a licensed dealer: 18 for rifle and shotgun ammunition, 21 for handgun ammunition.
• Non-toxic shot for all waterfowl hunting nationwide, and often on wildlife refuges for other species.
• State minimum calibers or bullet types for big game, and lead-free requirements in some areas.
• In some states, background checks, in-person pickup, or limits on shipping ammunition to a home address.
• Restrictions on armor-piercing, tracer, and incendiary ammunition.

Before a hunt, check your state wildlife agency's current regulations. Before you order, make sure the ammunition can legally ship to your address.