What is the average "lifespan" of an m16 bolt and carrier? Because new parts like these are hard to come by here, so we use mostly surplus M16 parts salvaged from used rifles.

I would tend to think the lifespan of a carrier would be practically infinite.  All the points that come into contact with any other part are either hard chromed or the part they interact with is softer.  Maybe if you where shooting in a sandy/dusty environment, the added grit would cause excessive wear.  As long at they are kept relatively cleaned and lubed, I can't see how one would fail to function.  The upper receiver would go before the carrier would.

Bolts on the other hand would be much more likely to eventually wear out.  If the bolt was properly made, the lifespan of the bolt would be controlled by wear on the rear of the lugs.  Eventually the wear would get to the point that headspace would become excessive.  Once again proper lube would help lengthen the lifespan.

The life is LOOOONG!  I imagine they may break before wearing out sometimes.  If you get nervous, get a Colt's Field gauge for M16's and check the bolts that look really, really worn.  Don't worry about the carrier.

Beware of the ATF. This is from http://www-2.cs.cmu.edu/afs/cs/user/wbardwel/public/nfalist/law.html. They state that possesion of an AR-15 and M-16 fire control parts is de-facto possession of a machine gun.

I believe the M-16 bolt carrier is considered part of the fire control group as the rear of the carrier is used to trip the full auto sear.

Slowworm


                  DEPARTMENT OF THE TREASURY
            BUREAU OF ALCOHOL, TOBACCO AND FIREARMS
                     WASHINGTON, DC 20226

                        MAR 25 1999                   903050:CHB
                                                      3311


Dear Mr. :

This refers to your letter in which you asked about possession of
spare M-16 machinegun parts by a person who possesses a registered
M-16 and a semiautomatic AR-15 rifle.

Any weapon which shoots automatically more than one shot, without
manual reloading, by a single function of the trigger meets the
definition of a machinegun in section 5845(b) of the National
Firearms Act (NFA).  An AR-15 rifle, which is assembled with
certain M-16 machinegun fire control components, and which is
capable of shooting automatically is a machinegun as defined.

The definition of machinegun in section 5845(b) also includes any
combination of parts from which a machinegun can be assembled if
such parts are in the possession or under the control of a person.
Thus, an AR-15 rifle possessed with separate M-16 machinegun
components can meet the definition of a machinegun, if the rifle
shoots automatically when the components are installed.

The fact that a person lawfully possesses a registered NFA firearm
does not grant authorization to possess additional non-registered
firearms.  A person who possesses a registered M-16 machinegun and
a semiautomatic AR-15 rifle and a separate quantity of M-16
machinegun components could be in possession of two machineguns.

                             - 2 -

Mr.

We would advise any person who possesses an AR-15 rifle not to
possess M-16 fire control component.  If a person possessed only
the M-16 machinegun and spare M-16 fire control components for that
machinegun, the person would possess only one machinegun.

We trust that the foregoing has been responsive to your inquiry.
If you have further questions concerning this matter, please
contact us.

                       Sincerely yours,


                      Edward M. Owen, Jr.
               Chief, Firearms Technology Branch

Don't think they have to worry about ATF where they are.

Three of my ARs have GI surplus bolts that came off of Viet Nam era M16s, and have had countless thousands of rounds fired thru them. They all headspace just fine.  People don't really understand just how tough these parts are. My own estimate is that a Colt, FN or other government contract bolt is good for more rounds that you can shoot thru one rifle without having to replace a barrel at least twice. Bolt carrier? Essentially good forever.

Won't try to estimate lifespan of aftermarket stuff. I have no idea how well or poorly they're heat treated. Only know I personally don't like 'em; and that's precisely the reason why all my ARs, no matter what brand, have Colt bolt heads in 'em[:D]

Latest bulletin that I received said to consider swaping bolts at 6000 rounds but to deffinatly do it at 10,000 rounds.  This was in ref to bolts in M4 carbines of course.
Carriers were not addressed.  The only problem I have seen with carriers is that the key comes loose and you need to re-tighten and re-stake the key if you dont have a new carrier to swap.  

Edited to remove an extra zero

[banghead]  Not this again!  It is not illegal to use an M16 carrier in your AR-15.  Slowworm, read the letter you posted again.  It says it is illegal only if you have the parts to assemble a machinegun (unregistered) which means it has to be able to fire more than one round with one pull of the trigger.  Using an M16 carrier will not do that, you have not created an machinegun.

In the second letter you posted, it only [b]advises[/b] that you don't have any M16 parts, it does say it's illegal - this is their way of recommending that you don't have ANY so that you don't ACCIDENTALLY have enough to make an MG.

Many people use M16 carriers in their AR-15's, legally.  The only thing illegal is if you have all the parts necessary to convert or create a machinegun out of an AR-15, and having an AR-15 at the same time, or if you have possession of a device solely and exclusively designed to convert a weapon into an MG, such as an LL or RDIAS.

"Definition of a machinegun law

26 USC 5845(b) The term ''machinegun'' means any weapon which shoots, is designed to shoot, or can be readily restored to shoot, [b]automatically more than one shot[/b], without manual reloading, by a single function of the trigger. The term shall also include the frame or receiver of any such weapon, [b]any part designed and intended solely and exclusively[/b], or combination of parts [b]designed and intended, for use in converting[/b] a weapon into a machinegun, and any combination of parts from which a machinegun can be assembled if such parts are in the possession or under the control of a person."

Yep, [url=http://ar15.com/forums/topic.html?b=1&f=6&t=147440]this[/url] yet again.

At the Colt Amorer's class the instructor stated that the bolt is good for 25,000 rounds before failure.

sunga_sy,

Just keep an eye on the bolt for cracks. There are penetrating dye test kits out there that work with black lights. They're designed to show minute cracks in metal.

Tweak, did the instructor have any comment regarding failure of the carrier?  I've always believed that unless the carrier decides to fail at the cam pin cutout they're basically a 'forever' item, key not included... [:D]  I'm using Colt M16 carriers in all my AR's and don't see any sort of appreciable wear, but it's always good to go to the source... You know what assuming can do for you... [;)]

Sounds about right to me[:D]

It never came up. I have seen incorrect BCs batter themselves on the ends of the cam pin cut. This usually manifests itself as broken cam pins. Only times I've seen carriers [b]fail[/b] was with kBs when the bottom separates.

How did I miss that one?  [:D]

What planet are you on???  Where the hell is "PHL"???

AR & M16 parts are a dime a dozen around here (America).

Try the Republic of the Phillipenes.  Duh!!!!