A great offering from MWG is their IK-520 40 round magazines. The mags are imported from Bulgaria and cost the same as a 40 round Magpul magazine. From MWG’s website:

• Designed by renowned development engineer Ivan Kolev, designer of the Bulgarian high capacity polymer AK Magazine.
• Increased Capacity
• Durable, Steel Reinforced Polymer Construction
• Ergonomic Waffle Design
• Stable, Level Follower
• Lightweight:  .4 Lbs
• Tested full and semi auto in M4, AR-15, M16A1, M16A2 Models
• .223 Caliber, 5.56mm

So how do they work? Well first off I wanted to see if they locked in and fit in my SCAR, a gun well known for being picky with magazines. Some mags have a tendency to raise the bolt catch just a tad that results in damage to the firearm. The IK-520 mags locked in without raising the bolt catch:

My friend Patrick and I took them to the range to see if they performed well and they worked great!

His M4 pattern rifle digested all 40 rounds with ease, regardless of how fast he pulled the trigger. The bolt locked open and they performed perfectly.

A few days later I did a few drop tests with no noticeable damage to the feed lips or expulsion of ammo from the body, so I suppose the steel reinforced lips helped in this regard.

Lastly, I decided to put my Wrangler against a mag:

As you can see the mag didn’t buckle or come out to bruised:

The mag still loaded all 40 rounds fine and there was no difference when locking the mag in.

So these are a great alternative to a PMAG and are priced the same, but for $18.95 most shooters will opt to buy the familiar Magpul brand mags.