Originally Posted by CharlieDeltaJuliet
That is why I precisely would not defend the Ruger as said earlier, I have no experience with them. The Hk is a considerable difference in temperature.
If that is in fact true (I haven't seen any data on it, so I would not know), I doubt the operating system is a major contributor to the difference. For example, the POF piston system runs much cooler than the DI; but it also uses a giant finned barrel nut that provides much of the cooling.
I believe the piston system will last longer due to les heat transfer and fouling. The wear is less. The standard usage life of an M4 before re barreling and bolt etc.. from the government is 8-10k rounds. The 416 is almost 4x that.
I guess I am missing how the operating system causes one rifle to have to be rebarrelled faster than a different rifle with a different operating system? Could you elaborate on that?
As to the bolt, the AR15 bolt is designed to be used in a 20" rifle under certain operating parameters. It was designed using 1960s metallurgy. We know that we can greatly enhance the life of the bolt simply by radiusing the lugs where they meet the bolt or by using higher quality metals like 9310 (or both). However, changing the bolt design means changing the barrel extension and tracking that part in existing inventories, so it won't happen. Changing the metal is an easier solution; but you have to overcome institutional inertia. The Knight's E3 bolt has run 20,000 rounds.
Frankly, I'll be interested to see how the HK416 survives in the military small arms maintenance system (which is the root of many of the current AR15 problems) and if it turns out to be as durable as the M16 once it gets treated like one on a consistent basis for 20 years. For that matter I'll bet you could shoot 4 M16s to death before you ever got one 416 back from H&K's service department. However, the HK416 isn't limited by the design of its bolt, barrel extension or metallurgy. The engineers were free to use what they could without having to worry about compatibility with the 20" M16 (except for magazines - and even that is arguable).
None of that has anything to do with the operating system though.
Also not buying the "But the SEALs and Delta use it!" argument. I know a SEAL who carried an M14 for years. He didn't like it better than the M16 or think it was a better rifle; he carried it because he did a lot of over-the-beach stuff and in that specific environment, the M14 was a better choice. And contrary to popular perception, he didn't have a Matrix-style arms room to choose from.