So many would have us believe the M-16/M-4 rifle's longevity is based on the "Forest Gump" principle in simply being in the right place and the right time to make history. Such cannot be the case as evidenced by the facts.
YES the M-16 was rushed into production over the objections of Military traditionalists - who of course did all they could to sabotage the project. So BEFORE we place the first shred of "blame" on any failing of the weapon itself we must look at those who sought to prevent Gene Stoner's "upstart" plastic and aluminum rifle from ever being a success.
There is nothing wrong with the basic design - a FACT proved out by it's being around going on 60 years later. Sure companies like HK bought out an aftermarket gas piston system, slapped it on and called it "new" and "revolutionary" but they changed nothing about the heart of the system.
The fact is, the M-16 family is probably about as ergonomically perfect as any rifle devised by human thought. I carried one for my share of years assigned to the 2/504th PIR and I came to appreciate exactly what Stoner gave to the world.
Way back when during the XM177 project days when the rifle carried a 1:14 twist and 11.5" barrel "everybody knew" the ballistic potential of the .223 Remington was restricted and this exacerbated by cold weather. Of course the Army crafted a rifle test in Alaska of all places with the clear intent of "proving" how ineffective the small cartridge and it's plastic rifle would be. They despised McNamara for basically seeing through their bull$hiT and ordering the rifle into production and the sabotage continued - really unto this very day.
The 55 grain bullet from a 20" barrel creates dramatic and devastating wounds combined with incapacitation exceeding that from a non-expanding .308 round. The A1 sight system was designed from day one to work perfectly using a 250 meter battle sight zero...so the Army changed that...went up in weight, cobbled up an overly complex (but kind of nifty) "800 meter" rear sight DESPITE ALL EVIDENCE DATING FROM WW ONE that 300 meters is the maximum practical distance a troop in the field can expect to reliably engage point type targets using iron sights. Oh sure, they NEEDED to go heavier on the bullet to use a "heavy" steel core...seriously? Lead is heavier than steel everyday including Sunday...they could have stayed with 55 grains, gone steel core and had a slightly longer bullet - base heavy of course to induce tumbling on tissue...but they didn't want that, that was too much in favor of the round.
Then we invade the Middle East and the very first thing our military brass think to do is SHORTEN the barrels from 20" to 14.5" thus duplicating the same sabotage they pulled the first time around! THEN they make a big deal about how ineffective the WEAPON is because of course they know their audience is composed of non-weapons oriented persons and even many who've served but bought into the nonsense that the only "real" battle rifle must be made of steel and wood, and fire a cartridge 4x more powerful than the average user in the field can EVER utilize. Yeah, that's the ticket, let's saddle the infantryman with some made-over M-14 where he can only carry 1/3rd the ammo! It's not hard at all to carry 1000 rounds of 5.56 ammo....how many armchair never been in the infantry and actually humped this stuff "experts" can grab up 1000 rounds of 7.62 and run with it - for long? When I was climbing up and down the mountains of Panama carrying my 200 rounds of linked M-60 ammo in addition to my own 460 rounds of 5.56 in mags plus more in my rucksack I APPRECIATED every single nuance that went into the design of the M-16 and still do to this day!
As a civilian I've built my share of AK's from parts sets and home-brewed receivers, to AR-15's from parts sets and store-bought and 80% receivers and the "rationale" for choosing the AK was always about cost...cheaper parts sets and much cheaper receiver stock...despite the FACT that the AK is erognomically atrocious...muzzle heavy, Cr@p sights, poor trigger, thin barrels, flexi-flier stamped receivers that really destroy any hope of accuracy. The BEST thing about AK's is the front-to-back mag lock up...IF the user doesn't panic and fail to insert it correctly, and the looseness of tolerances that helps it to function under adverse conditions...oh, and that huge gas piston that could care less about precise metering or excessive bolt thrust. Don't get me wrong, I LIKE what Kalashnikov did and his work is still walking around in the field for the same reason the M-16 family is...it works.
On the other hand I chose to build AR's when I could AFFORD the parts...ergonomically superior in every respect to EVERY other military rifle out there - WAY superior to the G3's ungainly, nose-heavy, 900 lb trigger...again there is a REASON the HK-91/93 went to dinosaurland and the M-16 is still alive and THRIVING! The ONLY rifle HK ever got right was the MP-5 carbine which is still ballistically inferior to even a short barrel M-16...and inferior in trigger an all other ergos. Oh wait, HK did get the "416" right...wait, that's an M-16! Only difference is the piston system and a few tweaks to try and pretend they didn't rip off the entire system...as they say, IMITATION is the sincerest form of flattery! I'd say a whole LOT of manufacturers are flattering the M-16 right about now...including the DIRECT GAS IMPINGEMENT system that works perfectly fine for hundreds upon hundreds of rounds as long as the ammo is using the powders the designer intended be used...yet ANOTHER point of sabotage in the M-16's history of development on the fly. The Air Force LOVED the gun, and of course the Army hated it...and have done all they can to bash it.
As for the cartridge, the only reasonable "replacement" floating around today is the 7.62x35 (.300 AAC) because it uses the same case head, smaller powder charges, more ballistically efficient projectile of heavier weight an the ability to launch super-heavy bullets subsonic for suppressed work. The .300 Blackout is also ideal for use from SHORT barrels, but when fired from LONG barrels the 5.56x45 has superior trajectory and therefore better hit probability.
Sure the DI gas system pumps more heat into the receiver...that's why it's made of 7075 Aluminum! That's also why Winchester developed a low-residue powder meant to be used. During the years I personally carried an M-16A1 into harm's way I NEVER had a malfunction of any kind. I have no idea how many rounds I fired at "one time" between cleanings, I just know MY M-16 never failed - not once, and there was no "rash" of rifle failures going on around me either...
Sure you can take an M-16 out and run mag after mag through it full auto until it fails...some dude on YouTube did it (it took a lot of rounds), but guess what, you can do the same with an AK...yes indeedy AK's CAN and DO suffer from parts breakage, stoppages due to chamber heat, failure to feed due to misaligned magazines and so forth...but then the AK has had 60 years of POSITIVE press from America, while the M-16 - which is actually only about 10 years "younger" in design, has actually managed to survive and THRIVE despite an establishment intend upon its demise.
The question is, what EXACTLY would anyone replace it with? Ergonomically it is already perfect. The cartridge's performance from rifle barrels is legend (by all but armchair experts), and the role of the personal weapon on the battlefield is pretty clearly defined. Until we advance to the next technology - phased plasma rifles, I don't see any radical redesign of what has clearly PROVEN itself...and as for being "cheap" the M-16 is by no means inexpensive to build. An all stamped steel rifle would be significantly cheaper to build...the AKM to be precise so the bunk about the M-16/M-14 still being around due to cost contraints is ridiculous...the AR-18 was indeed "cheaper" to build but lost out because it sucked...I was around when it was trying to become popular but never did....and for good reason.
The HK series were ungainly.
Beretta's AR80 was an ungainly abortion.
The M-14 is far more wonderful in memory than during it's almost non-existent service life...because it was nothing but a "stop gap" on the path to the M-16. It didn't take smart people who faced the AKM in Vietnam to realize the M-14 was last century's technology...too heavy, wood stock (rots away in about 10 days in a jungle), too large of a round for what the mission requires making the gun far larger and heavier than needed. POORLY designed gas system that promoted inaccuracy unless specially attended too by an expert tuner....full auto was a JOKE due to recoild and barrel whip. One FACT lost on those who don't understand the DI gas system is that it makes the M-16 HIGHLY accurate right out of the box...because there's no piston system creating a neutral/positive pressure cycle on the barrel...oh and let me not forget the M-16" barrel can be changed IN THE FIELD by anyone with a wrench...all precision headspacing is done in the factory UNLIKE the M-14 which of course is based on "old-timer's" technology where the headspacing must be set as the barrel is screwed into the receiver...a VERY clunky system that was completely swept away by the far more effcient M-16 system...LOT's of guys can build their own M-16 in their garage with nothing more exotic than a barrel wrench...can't do that with an M-14 that's for sure! While much is mad of the headspacing issue I've put together at least 50 M-16 style rifles over the years and not ONE has ever been out of spec from the factory...not one. I can pull the bolt from one of MY AR's right now and drop it into another and the odds I'll have a headspace problem is about as close to zero as statistically possible...can't say THAT for the M-14.
If I had to "bug out" tonight would I take my Browning .30'06 BAR? NOPE! Would I grab my 7.62 AK? NOPE! Would I grab my 5.45x39 AK74? Close, but NOPE! Would I grab for ANY bolt action in my safe? NOPE! I'd grab my AR-15 with scads of ammo because it embodies the very TIP of modern technology...lightweight, high capacity, reliable, precise and accurate, the ammo is light meaning I can carry more of it.
All hype and all BS aside the REASON the M-16/M-4 is still around is because despite efforts to sabotage it, it works too well...it gets the job done. Every other rifle built over the years to compete with it or replace it has gone extinct...because they were all technological dinosaurs at birth...Galil...anyone rememer that ***? A special Israli modified AK platform with better sights and a decent barrel?
Styer AUG...now THAT's a system that's ALL HYPE and little delivery...which is why it's basically ignored by everyone except Americans with enough cash to waste on a civilian version.
What the M-16 "needed" it got...proper ammo, proper understanding that it needs to be cleaned once in awhile, and thanks to the CIVILIAN market, proper magazines that are better built and fit better which overcomes the platform's only real weakness...the sloppy fit of original contract magazines that led to FTF and double-feeds.
For all the armchair commandos pontificating on why the M-16/M-4 should not have survived this long the bottom line is...it's BETTER than everything else out there!
To those "experts" who like to malign the cartridge I would draw attention to Miami 1985 and little confrontation between the entire Miami FBI office and two small-time bank robbers - one armed with a Mini-14. The round is plenty effective...anyone who disbelieves this is free to run in front of one to prove their own personal manliness!
