What 
Everything had/has(?) a shelf life. Even hard items like a weapon.
You and I may not agree with the assessment but that is the way it was, at least. May still be. But that was at the time of the Viet Nam fracas winding down or over and there were apparently excess stores of weapons and it was explained to me when I questioned it that everything has a shelf life. Plus storage was expensive, etc, etc.
Different time, different world.
Not much different from M14’s being chopped up.
I’ll admit this is a rather bizarre statement considering I have fired M16’s from Vietnam. Not to mention many weapons like M14’s were sent to depots, overhauled and then sold to foreign countries or mothballed.
Weapons are usually re-used until they fail gaging or some other dimensionally problems arise. I fixed weapons in Iraq that were damaged in combat and during IED attacks, they weren’t scrapped out.
I thought the whole thing was bizarre.
But it was a long time ago and was truly a different time.
Nobody needs to put much stock in it, but, going along with the thread it just says that at least at one time supposedly good weapons were destroyed on a ‘time in service’ basis.
Odd, too.
Especially when you think of WWII era BIG gun barrels still being used for other purposes.
Incidentally the destruction of perfectly good M14’s is well documented. Lee Emerson’s book is one documentation. 750,000 destroyed between Crane and Anniston. ( Page 97, second edition).
The NRA used to write about it also.
I’m not trying to be argumentative here, just relaying a weird thing I supposedly learned about and the well documented M14 info.
Armorer courses vary depending upon whose course it is and who is teaching it. When I and our staff teach armorers courses we see a vast array of weapons, which allows all students in the class to see the differences in the weapons as well from an internal perspective of how the weapon was made. In courses we do make suggestions as to the minimal lifespan of parts based on several decades of studying parts. We see variances in the life of the parts and assemblies depending upon how the rifle is handled in the field, maintained for cleanliness to greatly include lubrication (where/how/which lubricants), quality of the parts, how well they are machined, quality of the original assembly of the rifle, what materials the parts are made from and how they are machined (huge differences here sometimes), variances in semi-auto -vs- full auto fired weapons, and ammunition selection. In the armorers class and manuals we provide a lot of numbers of the minimal lifespan of parts which is based on an average. We show examples of rifles that were worn out to the point of being locked at 2500rds from brand new, due to improper maintenance though bad cleaning and lubricating with the not so AR15/M15 lubricants like wheel bearing grease. We do see rifles that go greatly longer than their minimal round count of which we attribute to maintenance and operation, example is that we have several rifles that are running on the original bolt assemblies at 95k rounds. My suggestion is to first make sure your rifle is properly assembled, maintain your rifle with regular and thorough cleaning using good tools/cleaners/lubricants, and inspect things to make sure they are not being worn (like a action spring that can show wear at about 12K, and if continued use will cause the action of the rifle to be more violent which can cause problems with wear and stress). Regular maintenance is a must with a good thorough cleaning and lubrication, heavy carbon deposits on guns that are run dry will show wear, as compared to a wet lubricated gun. I recommend doing a full inspection of the rifle on a regular basis and always do so if the rifle has been used hard or been exposed to harsh conditions to include being dropped in sand/dirt and something similar, you should include gaging, and if you have access to a bore scope then use it as well.