top-quark.blog
AR-15 Bolt Takedown & Discussion
Wed, 12/31/2003, 19:54I had a bit much time today, and decided to make a guide to the AR-15/M16's bolt/carrier assembly... This way I can at least pretend that this blog is useful.
The AR-15 bolt/carrier assembly is in many ways the most critical portion of the AR-15 weapons system. It is involved in the duties of feeding, firing, and extracting ammunition in the rifle. Though much maligned for its direct gas impingement mechanism, which tends to result in a dirtier action, the design does incorporate some self-cleaning attributes to maintain reliability. These mechanisms alone, though effective, are designed more for stressful field conditions when regular maintainance might not be possible. Under the conditions most civilian shooters see, it's wiser to maintain a procedure for cleaning, rather than risk lessening the lifetimes of these expensive arms..
A consideration to make when cleaning firearms is that there's no need to be overzealous about grime; there's no drill sergeant barking over you. In fact, the better part of firearms wear is due to overcleaning. Ex-military types are especially prone to this; one has to keep in mind that firearms maintainance skills acquired in basic training are in large part a method to instill discipline.
Disassembly
We start with the bolt/carrier assembly, taken from the upper receiver. It's usually covered in all sorts of soot and dirtied oil, so a rag or paper towel is used to wipe off the most offensive areas.
We flip the bolt so that the left side faces us ("left" being relative to its position when viewed from the weapon firer's perspective). Using a fingernail or some other implement (screwdriver, in this case), we remove the firing pin retention pin and set it aside.
Now that the firing pin is no longer captured, it can be removed from the assembly
The cam pin is then removed; this involves first pushing the bolt into the carrier assembly, as illustrated, then rotating the cam pin from its "horizontal" orientation to it more "vertical" orientation. You can't lift it out if you've got it wrong, though, so experiment if you have to. It helps to use the firing pin to rotate the cam pin if you've got gloves on, or are less dextrous (fat fingered!)..
Once the cam pin is removed, the bolt can be pulled forward of the carrier.
At this point we've disassembled the bolt assembly as far as is normally required for regular maintainance... but if we want to go farther, disassembling the bolt isn't too hard...
Using the firing pin, we push out the pin retaining the extractor. This can be done from either side.
The bolt is now disassembled as far as you should ever need to. Any farther, and you'll need more tools. Re-assembly of the bolt and carrier assembly is exactly the reverse. Make sure to pull the bolt forward before you insert the assembly in your upper, though, otherwise the cam pin will interfere.
Analysis
Within the bolt, it's interesting to note a point of failure in the AR-15 system. The extractor springs in most AR15 bolt assemblies are fairly weak, and this can lead to various extraction-related failures. One of the few high points about Colt assemblies is their usage of higher strength extractor springs. You can tell the difference by looking at the inner plastic insert. "Normal" springs feature a blue plastic insert, Colt strong springs have a black insert.
Owners of low power extractors need not despair, though.. salvation can be found in purchasing higher power assemblies from Colt suppliers, or Wolff Gunsprings. If you're a poor college kid like me, though, you've probably seen the blue rubber "D-fender" (example link) and wondered just what's so special about that "polymer" of theirs. Well, "nothing".. Just go to a hardware store with your extractor and pick out an o-ring that fits over the spring. I forget exactly what size it is, but it's a good fit, and improved extracting in my previously ailing carbine..
The o-ring installed on the weak spring, alongside the Colt extractor..
Last thing to consider.. Even with the best of precautions, failure can always occcur! A spare carrier assembly could salvage a bad range day, or maybe even save your life. Most military types like carrying at least a spare bolt. At very least, tape a spare extractor to the inside of your pistol grip; it'll stay out of the way, and still be there if you need it.
Comments about "AR-15 Bolt Takedown & Discussion" :
Not a bad article for somebody who loads bullets backwards...
-left by Da_Bunny ( )
Dear Nal, thanks alot for the informative web page! You definetely know your stuff. Your hands are kinda cute too. Anyhow, when I get my AR15 tool kit Im gonna try to put this good information to work. Toodle-loo Your pal, johnnymceldoo
-left by johnnymceldoo ( )
Not a bad article for somebody who loads bullets backwards...
-left by Da_Bunny ( )
Thank you for the detailed information. I was unaware that the extractor spring was a problem area. The M16A2s that I carried and fired while serving in my beloved Marine Corps never failed in any way. I will be sure to watch for this in the future. Take care and I wish you good fortune.
-left by Maddogkiller ( )
J_Smith at AR15.com
Good article - thanks for the detailed info. - as always a good read and very helpful
-left by Jon Smith ( )
Good Article. You may want to add that when putting the cam-pin back in, make sure the bolt isnt backwards. Some bolts can allow the cam pin to insert even if the bolt is backwards (extractor on left instead of right).
-left by spc-ops ( )
Very nice ,neat well labelled article it was a great help to me
-left by Mike Moser ( mjgm@comcast.net)
Is there a trick tor re-installing the firing pin retaining cotter key? I have managed to ruin the original by not being able to reinsert it without damaging it. Have installed a hardware store cotter pin cut to the right length as it's only function is to hold the firing pin in place. Have purchased a new factory pin but don't want to ruin it. Jim
-left by Jimbo ( N/A mail jdm50@earthlink.net)
There's not really a trick; you just need a pin in good condition. Sometimes, you can rotate it as it goes in. If the pin's starting to spread, you can sometimes squeeze it back together. Also, you can work on the beveling on the end of the pin, given that the "receiving" end in the bolt carrier isn't chamfered. Ultimately, though, the cotter pin is a disposable item; if you get them from some of the more popular online vendors, they're about a buck each. Seeing as they last thousands of rounds, I think it's a decent investment.
-left by admin ( http://top-quark.com/)
Great article - What is your opine re solid retaining pins vs cotter pins? $12.95/2 Is this a good way to go? Thanks, GT(USAF RET)
-left by GLENN THOMAS ( )
Thanks. Happy accident---stumbling into your pictures while in the midst of my first takedown....or whatever it is called, in the world of "Tacticals".
-left by Hemmetoid ( )
Helps me been a long time since I had drill sergant barking at me. Thank you for the information.
-left by ANDY ANDERSON ( )
Thanks! Really help full and great article.
-left by Will ( )
The D-Fender and Crane extractor O-Rings are special in the sense that they are made of Viton, which is heat- and chemical-resistant and will last longer in your weapon.
-left by Gunmetal ( )
Btw, here is a thread with a lot of good information regarding the O-rings. http://m4carbine.net/showthread.php?t=435
-left by Gunmetal ( )