I just bought a 24"upper wich said its fully headspaceg and gauged. Can I swap out the bolt carrier assemblie from my bushmaster m-4?

Yes, you can.

should be no problem, but for safty sake, check the headspace on the one you're installing it in.

I agree with 71DL. Call Brownells, get their field guage, and make sure your headspace is okay. I've only seen a very few bolt and barrel combinations that weren't, but for $10 or so I'd want to know my eyes were safe.

You do realize, of course, that while swapping bolts works okay 99.9% of the time, the wear on your bolt and barrel extensions may--I say may--be increased because the lock-up is probably just a little different from one upper to another. Kind of like taking internal parts from one car engine and putting them into another--they'll work, but may wear a little faster because they fit a little differently.

If you shoot a lot, I'd recommend you have a dedicated bolt for each upper, and if you want to save a few bucks you can use one bolt carrier for both with no problem.

Good shootin'.

I recall reading on my bushmaster manual that swamping bolt carriers between rifles make cause explosion.
I'd say buy a new bolt carrier....it's cheaper than a new AR if you should screw up you old one, and swamping carriers is definatly not worth your life.

BS, and if it is in the manual, they should know better.

BS BS BS BS

His Bushy M4 is of recent mfg, not some parts from who knows where, worn out.  Even if the headspace is not perfect, it is not going to blow up.  

The preoccupation with headspace and military rifles comes from gunsmiths working on old worn out WWII bolt actions, sometimes fitting new barrels, and trying to get the headspace correct.

If this guy's bolt is safe in his M4, it is safe in the new upper, too.

BTW, the bolt carrier has nothing to do with headspace, only the bolt and barrel assy.

EXACT excerpt from Page 25 of Bushmaster XM15 Type Rilfes Manual:



"[B]CAUTION[/B] Bushmaster does not recommend the practice of swapping bolts between different rifles. Doing so could result in damage, personal injury or death."



and yes, "A_Free_Man" I [b]DO[/b] think bushmaster knows more about this matter than you do.

I'll bet the Bushy manual, like my Oly manual is more about the manufacturer doing typical CYA than practical advice. Can't really blame them though...I'd hate to pay their product liability premium! I've swapped bolts with no problems and won't hesitate to do it again if the parts in question aren't "high mileage". If you're uncertain then by all means check headspace...be sure you know how though...supposed to do it without the extractor and ejector. While I've nrver pulled and reinstalled those, it looks kind of tricky. Bottom line is it's nice to have dedicated bolt and carrier assemblies for each upper but not always absolutely necessary. Lokedon's "EXACT" excerpt didn't mention the carrier because as A_FREE_MAN pointed out there's no relationship between the carrier and headspace. Seems like headspace is kinda like barrel torque...always plenty of opinions!    

I've swapped bolt/carrier assembly from one upper to another from time to time without any problem.  You'd more likely to run into a KB situation from overpressure ammo than improper headspace.

Just for the record, about 1 1/2 years ago I bought 4 well used GI bolt assys from a parts house in Arkansas.  Three were Colt and one Vietnam era govt contractor. Tried each of them out in all four of my ARs (two Colt barrels, one Bushie barrel, one Rock River barrel)

All four closed on the GO guage. Three of the four did not close on the NO GO guage, and the one that did close on NO GO did not close on the FIELD guage. It was also the oldest and most well used looking on the bunch.  So old, in fact, that it still had the original white extractor spring insert; and they changed over to the stiffer blue ones about 1968.  Put in stiffer extractor springs, and am using two of them in my rifles, w/two spares for future projects.

As noted by earlier writers, carriers are totally interchangable, and my own experience is that bolt heads probably are also, IF you're using GI spec parts. Re commercial pieces, Colt and Bushie bolts are certainly made to Govt. specs.  Other brands? Probably the well known brands, but who knows for sure??

Lockedon, hate to say this but you proved yourself wrong with you're own quotation from the manual. A_free_man was talking about swapping bolt carriers between weapons being o.k. You quoted a statement from the manual that was referencing the bolt and not the bolt carrier.

Personally I would spend another $120 and buy a new bolt and carrier assembly from bushmaster instead swapping the part between two rifles.

Hmmm....



I stand corrected...

If the bolts are good quality (and his is from a Bushy M4, which is a relatively recent model), and not worn out, it will work just fine in both barrels.

Kabooms do not happen from excessive headspace.

While we are quoting manuals and such, I refer you to Armalite Tech Note #11:

"There are a number of popular misconceptions concerning headspace, notably that the tighter the headspace, the better, that loose headspace is dangerous, and that one particular dimension is best.  None of these common beliefs is totally true."

"Insufficient or excessively tight headspace tends to cause malfunctions such as failure to lock.  It often makes extraction difficult and can cause dangerous stresses on the mechanism that shorten its life expectancy or lead to failure.  Excessive headspace may lead to gas leakage around the case or head separation and the sudden release of high-pressure gas.   Most shooters fear excessive headspace, but it is actually insufficient headspace that is more dangerous.  A good firearm design can actually tolerate a great deal of excess headspace."

"While the SAAMI example above demonstrates that a fairly wide range of dimensions work, manufacturers narrow their tolerances to conservative ranges that allow a reasonable combination of safety, reliable function, accuracy, and useful life."

For SW99 to have a kaboom from swapping bolts would be less likely than winning the Powerball.  If a kaboom occurs, it will usually be from a high primer, or other ammo related problem, not from the rifle.

The best deteminant of proper headspace is to examine fired brass for shiny rings just above the case head.  Those rings are signs of the case stretching.

I have about 30 years experience with handloading, and about 40 years experience shooting firearms of all types.  As a child, we had to clean the reloading gear off the kitchen table to eat dinner at night.  There were haybales in the front yard (about an acre) where Mom shot archery, and we shot clays every afternoon out back, and shot at the skeet club on Sundays.

I have enough years of experience with the AR15, shooting and building them, that I make the statement with full confidence, yes, he can even swap bolts.