AR-15 Weakness

The AR-15 is an accurate, ergonomically well-designed rifle, and it has proven to be a reliable design. However, when subjected to extreme conditions of dust, dirt and sand, it has proven to be somewhat more prone to failures to feed than, for example, the AK series of rifles. Most people attribute this to the direct-impingement gas system, as compared to the piston/operating rod system of the AK. The real culprit is the cam pin, which can drag on the side wall of the slot it rides in, especially when the bolt face contacts the top cartridge in the magazine in order to strip it from the magazine and feed it into the chamber. This drag slows the forward movement of the bolt/carrier assembly. Add dirt to increase the friction, and this can slow the assembly enough to cause a failure to feed.
At least one company now sells a cam pin with a sealed bearing on the end instead of the fixed rectangular head of the standard pin. This allows the pin to roll, rather than slide, along the slot it rides in.
Another option would be to spring-load the bolt to prevent the pin from contacting the wall of the slot. The buffer spring rate would need to be increased, so as to overcome the bolt spring and allow the bolt to go fully into battery.