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What Kind of Ammo Should I Buy?

Well, that’s a loaded question (sorry for the gun pun).

Whether you have an AR-15 already, or you’re planning to acquire one in the near future, you need to know what kind of ammunition to feed it to keep it happy.

First, let’s talk caliber…

If you’re not sure what caliber your gun is designed for, there’s a couple ways to check. You’ll want to look at the magazine well, typically under the manufacturer name or logo you’ll often see the caliber listed. The vast majority of ARs are chambered in .223 or 5.56 or both, but more on that later. There are numerous other options available… .308, 300 Blackout, .223 Wylde, 6.5 Creedmore, even pistol calibers like 9mm. But these are less common and typically more expensive than your average Armalite… and If you have one of these, you probably know it.

Your lower may say something like “CAL MULTI” because it is possible to run more than one caliber on a certain model of lower. On an AR-15 platform lower it is possible to shoot .223, 5.56, .300 BLK, .223 Wylde because they’re all similar in size and some of them can even use the same magazines! (an AR-10 platform is designed for the bigger bullets like .308, 6.5 Creed etc)

Lower Markings showing caliber info

This is where things get dicey: What round is your barrel/upper designed for?

I’ve yet to see a gun that doesn’t have the caliber carved into the barrel somewhere. Give it a good look, you’ll likely see something like “5.56 NATO” etched into the barrel. Bingo.

You may use .223 Remington (Rem) in a 5.56 NATO barrel/upper receiver, but you should NEVER use 5.56 in a barrel designed only for .223!

5.56 is made to Military Specification(Hence the North Atlantic Treaty Org designation).

.223 REM is made to the SAAMI (Sporting Arms & Ammunition Manufacturing Institute) specification.

You may use .223 Remington (Rem) in a 5.56 NATO barrel/upper receiver, but you should NEVER use 5.56 in a barrel designed only for .223! The chamber on a .223 is slightly smaller than that of a 5.56, which means putting 5.56 ammo into a .223-only chamber can result in damage to your firearms and dangerous shooting conditions. It may cycle just fine, but this is a risk that we do not recommend taking. Sure, you could drive 90 mph on your spare tire that is only rated for 50mph, but that doesn’t make it a good idea.

Let’s say you have a rifle that is stamped “5.56” like most AR’s out there, you can shoot .223 or 5.56. Moving on to bullet weight!

Bullet weight, which is denoted by “grain” gives the bullet different characteristics as it travels down the barrel and therefore also at it moves down range. In the .223/5.56 world, weights range from 40-77 grain.

For the best accuracy, bullet weights are recommended by the “twist” on your rifle’s barrel. This the the ratio of turns in the lands and grooves or “rifling” inside. (This is where the term rifle comes from, as opposed to smooth-bore firearms like muzzleloaders and shotguns)

This information will generally also be stamped onto the barrel.

Helpful diagram for determining ideal bullet weight for barrel twist.

Case material/quality

“I run nothing but steel case Tulammo because it’s cheap and I like to shoot a LOT!”

We hear this a lot. Yes, you can buy steel case ammo for your AR for typically around $0.22/round; But steel is harder than brass, and has more friction. This translates into greater wear and tear on the internal components of your gun, and carries a higher risk of malfunctions. Our personal experience with steel-cased ammo is that it isn’t worth the modest cost-savings. Brass ammunition can be had for around 0.26/round; and it much less harmful to your firearm. Steel cases are coated in a lacquer to cut back on the friction, this lacquer will warm up in a hot gun. If you have a malfunction such as a  failure to eject, a steel case can become lodged in the barrel and when the lacquer cools it will set up like glue. It is the opinion of this writer that steel case should be avoided.

Specialty ammo

There are specialty ammunitions out there with specific purposes in mind.

The popular XM855 by Federal, known as “Green Tip” or “Lake City”, falls into this category. This is a 5.56 Mil-spec round with its tip famously painted bright green. These rounds are designed to penetrate materials that would typically cause expansion of other rounds, which causes them to slow down and stop. “Green Tips” will go thru thin steel, drywall, and human targets with ease, making them a poor fit for home defense and plinking on most steel targets. You don’t want to be “that guy” at the range that left the thin steel targets looking like Swiss cheese…

Contrary to what many of your range buddies might tell you, Green Tips are NOT classified as “armor-piercing”.

An XM855 “Green Tip” that has been dissected.

Specialty defense rounds like the Hornady Critical Defense .223 REM have a hollow tip like handgun caliber hollow points, which are designed to rapidly expand even when hitting softer targets such as drywall, car doors, and home invaders like Harry and Marv from Home Alone. 

There’s of course other exotic stuff out there like tracer rounds, (great for starting brush fires!) starburst rounds (even better at starting brush fires) and fragmenting defensive rounds, but that goes beyond the scope of what we are trying to accomplish in this article.

Have a question? Have something to add to the conversation? Leave a comment below.

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Written by Evan Hartman

Evan lives in the Midwest with his wife, son, and Siberian Husky. He is passionate about assisting others in exercising their Second Amendment rights. He has been active in shooting and collecting firearms for nearly a decade. When not working, shooting, or building, you might find him playing guitar or sipping bourbon.

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