Short answer: polymer magazines are tough, light and often have windows to see rounds. Aluminum magazines are slim and proven. Both work when the follower, spring and feed lips are good.
Polymer
Resist dents and corrosion, and many have a window or ribbed body. They can be a bit thicker, which matters in tight magwells.
Aluminum
Thin and light, and they fit nearly every magwell. Dents can hurt feeding, so check the body and lips.
What to check
Follower type, spring, and whether the magazine is made for 5.56 and .223. For other calibers see the AR magazine compatibility guide.
Buy several
Test every magazine with your rifle. If one fails, replace it rather than blaming the rifle.
How an AR-15 magazine works
An AR-15 magazine holds rounds in a staggered column. A spring pushes a follower up, the follower pushes the top round against the feed lips, and the bolt strips that round forward into the chamber. The feed lips set the angle the round enters at, so bent or worn lips are one of the most common causes of feeding trouble.
Capacity and calibers
The common sizes are 20 and 30 rounds, with 10-round magazines also sold. Magazines holding 40 or 60 rounds exist, but very long magazines put more load on the spring, so reliability depends heavily on the maker. Most 5.56 NATO and .223 Remington magazines are interchangeable. Other chamberings, such as 300 Blackout or 6.5 Grendel, may need their own magazines or a specific magazine marking, so check the product page.
Choosing by how you shoot
- Range and training: buy several of the same model so every magazine behaves the same and you can swap freely.
- Hunting: a low-capacity or lightweight magazine is easier to carry and often a better fit for the rifle’s balance.
- Competition: look at how fast a magazine drops free, how it seats, and whether the base plate helps you grab it.
Troubleshooting feeding problems
If a rifle fails to feed or the bolt does not lock back on an empty magazine, test the same magazine in a second rifle. If the problem follows the magazine, check the follower for tilt or cracks, the spring for weakness, and the feed lips for damage. If it follows the rifle, the cause is more likely the gas system, buffer or lubrication. Marking your magazines with a number or a paint pen makes it easy to find the one that causes trouble.
Care and storage
Wipe the inside of a magazine dry and clean when it is dirty. You do not need to oil the inside. Magazine springs wear mostly from repeated compression cycles and heat, not from sitting loaded, but rotating your stock is still a good habit. Store spare magazines in a dry place away from heat and moisture.
Keep building
Browse AR-15 parts, read the custom AR-15 build guide, or let our Palmetto, FL shop help with gunsmithing and custom AR builds.
Shop AR-15 parts at BMTC USA, a gun shop and gunsmith in Palmetto, FL.