If it were me, and money isn't a problem, I would buy a factory Colt M16/A1/A2 first. If you've got enough cash for two, buy an RDIAS next.

The lower receiver of an AR –– the expensive part –– is not a stressed part. If you use quality ammo and in-spec uppers and accessories, you just can't shoot enough to wear it out. There are Vietnam-era M16s still in use by .gov, now mostly for training (which means they have to put up with all a green recruit can do to 'em). They keep going and going.

There are a couple of range-rental M16s still running fine after documented 250,000 rounds down the tube. Not the original upper, of course, but the receivers are still fine.

There is always the chance of a kaBOOM, particularly if you use crappy ammo or worn/out-of-spec components. FWIW, though, I have never seen an M16 lower receiver damaged beyond repair by shooting –– uppers do get trashed, but the lowers usually remain intact. And remember, that tiny $12,000 piece of metal (RDIAS) attaches to the upper receiver lug: If the upper grenades, good luck finding the RDIAS, which could be thrown anywhere.

Factory M16s are also pretty much plug-and-play with any milspec or Colt upper. That's not true for RDIAS, which often require "shimming" or timing for each upper. And I hate finicky guns –– when there is a 100% reliable alternative, I'll take it.

FWIW, I bought the Colt M16A1 below in 1994. It was ANIB. Since then, I've prolly put more than 50,000 rounds through it in 5.56 and 9mm, with dozens of uppers, from the DOE 9mm shown to a Colt LMG. I change all the springs every 5k of 9mm or 10k of 5.56. The finish is original and after 50k rounds in 15 years, has probably dropped from 99% when I bought it to 96% now. I don't baby it, but I don't throw it around, either. For that matter, I don't throw around any gun.

As always, Your Mileage May Vary.

First, FYI, I moved this thread to the M16 Forum (which also covers RDIAS). You should check out the stickied threads at the top of the forum –– they should give you a better handle on things.

Some thoughts on shopping for a Colt M16:

–– Stay away from refinished or reanodized guns unless you know the gun and owner personally. First, the market value is less (Colt MGs are collectibles, after all) but second, and more important, it may be hiding repairs or rewelding work. Receivers can be repaired by a talented welder so you can't see a weld short of x-raying the receiver, but a weld in aluminum always introduces a weak point in the metal (compared to the original one-piece forging). Why risk it on something this expensive?

BTW: There are some moly finishes which look very, very much like the original factory finish. Sometimes, the only way to tell moly from original is by touch: Moly is a surface coating and has a very slight spongy "give" when you gently press a fingernail against it; the factory Colt anodizing has no such "give." (I didn't figure this one out until I had examples of both finishes side-by-side, and needed to find a reliable test for refinishing.)

And one more note: Colt shipped many guns with uppers/lowers that do not match exactly in color. So you can't judge originality by that, either.

–– If you check the serial-number thread in this forum, you'll see that Colt reserved certain serial-number ranges for different customers. The nine-million range was for law enforcement/export M16A1s, and the eight-million series for LE/export M16A2s. Guns in this range went direct to commercial U.S. distributors and often were sold instead to civilians. When you come across an NIB or low-round-count M16, it will probably be from one of these ranges.

M16s in other serial-number ranges may have seen military or .gov use –– nothing wrong with that, but again, it's much more difficult to find one that is truly low-mileage. And some of these were demilled by cutting, then welded up and registered as transferables. After decades and often multiple owners, sometimes even the sellers don't know it's a reweld.

–– A civilian-owned M16 can have a lot of rounds down the tube and still look near-new. (See mine above.) That's because many owners (me included) strip the gun down to the bare lower receiver as soon as they buy it, and carefully store away all the original parts. Then they build them up again with brand new parts, right down to the last spring. As noted, the lower receiver is a no-stress part, so unless it has been abused, it's difficult to tell the round count (and if the owner reinstalls all the other original parts before selling, it's even harder to tell).

–– Obviously, check around the front takedown pins for cracks; other potential crack locations are vertical ones in the front wall of the magwell, and in the receiver's rear "hoop" where the receiver extension (buffer tube) screws in. The takedown pins and/or magwell can crack if the upper receiver is pivoted open and then the gun is dropped. The rear receiver hoop can crack if the gun is lying on an uneven surface and someone drops something heavy on it, like a full ammo can.

–– The inside of the magwell is a good indicator of use –– you can't shoot without inserting mags. Then again, they could be using Orlites or other plastic mags, which don't scratch the insides. And an original-finish receiver with more wear inside the magwell than on the outside of the gun tells me it had a very careful owner. That's a good thing.

–– Last, but not least, check the holes in the receiver wall where the hammer and trigger pins sit. I do this with a magnifying glass. The holes should be perfectly round and the edges of the holes absolutely flush with the surrounding metal. If the gun has been run with 9mm or 7.62x39 uppers that were not properly set up, or run with weak hammer springs, the hammer can impact the disconnector and pass the impact along to these two pin holes. The result starts as a slight "wall" of metal building up on the outside edge of the hole; eventually, the round hole turns into an oval.

If the holes are damaged, they can be drilled out and bushings installed. That fixes the problem permanently, and is not expensive to have done ... but again, on a Colt where some of the value comes from collectibility, such repairs detract from resale value.

That's a quick rundown ... I'm sure others will chime in here.

Actually, I agree with you.

My concern is that some folks love RDIAS because you "can't blow them up," therefore you can abuse the host as much as you want, use out-of-spec parts and the cheapest battlefield-pickup ammo ... exactly the ingredients to create a kaBOOM ... and ignore the fact that if you can't find the RDIAS afterward, you can't use it.

OTOH, if you use quality parts and quality ammo, and take care of your gear .... you prolly won't wear out the RDIAS-host gun, either. That's the same approach I use with my RR.

FWIW, I know of two cases over the years where owners literally lost RDIAS –– one found his months later, hiding in a corner of his safe; the other apparently had a hole in his pocket; it hit the ground somewhere and was never found. In addition, I have seen several "replacement" RDIAS that obviously were not made by the 07/02 listed on the paperwork (in once case, this was verified by the 07/02 himself). I have no idea what happened to the original, but given ATF's stance on replacing transferable MGs with new-production clones, I wouldn't touch them. There also are RLLs out there that have mysteriously transformed into RDIAS –– the SNs are in RLL sequence, not RDIAS.

I grew up as a car guy as well as a gun guy, and got my license just as Carroll Shelby started making AC Cobras. Always wanted one, but never could afford one. Today, I could buy/build a repro which would outperform an original in every way. But I'm just not interested in clones –– I prefer the real thing. It's purely an emotional decision.

Which is why I'm happier with a Colt factory M16A1 than I would be with an RDIAS.

As always, Your Mileage May Vary.