Direct Impingement firearms have a questionable existance in the military industry since the design is more than 60yrs old, but the Magpul P-Mags have possible extended the life of them since the reliability of the magazines has also increased the reliability of the firearm.   Magpul P-Mags can take a beating and still run strong.   Check out some of the tests people have done with them on youtube.com

Rifle and pistol magazazines  have evolved as much as firearms have evolved in the last 100yrs.   They basically look the same, but they are stronger, more reliable and better thought out.   One of the  biggest advancements in firearm evolution were Glock Firearms.   The biggest evolution in rifle magazines are Magpul P-Mags.    There have been other similiar rifle  magazines made out of plastic, but the Magpul P-Mags are King.