# M-16/AR-15 operating mechanism **URL:** \ **Category:** Factual Questions\ **Created:** [July 27, 2010, 1:48am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134 "2010-07-27T01:48:56Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [July 27, 2010, 1:48am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/1 "2010-07-27T01:48:56Z")
Is there any advantage to the M-16’s T-bar pulling system? Most assault rifles require the shooter to cycle the weapon by gripping a handle to the side and pulling, possibly pushing forward as well. Why did Stoner choose to use the T-bar, which then requires the use of a forward assist? Was anyone else trained to take the magazines out with the left hand, pull the T-bar with the left, push the forward assist with the right hand and then close the port cover with the left hand? Also, do you think the direct impingement was worth it over the piston system? ---
**Author:** ![Todderbob](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@Todderbob](https://boards.straightdope.com/u/Todderbob)\ **Post date:** [July 27, 2010, 2:00am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/2 "2010-07-27T02:00:59Z")
This seems like part GQ, part IMHO… so if there’s some opinion in my post, that’s why. The AR platform shits where it eats. It literally fires burnt carbon and particulate matter into the action in order to cycle the bolt, which I think is a massive disadvantage. This is negated by an extensive infrastructural support for cleaning and maintaining the sidearms, but it’s something that has to be factored in, either for a personal purchase or for a military one. I wasn’t trained to use the AR platform in combat, so my reload has always been Drop Mag (Right hand) while (left hand) puts empty away and grabs new mag, left hand goes back to position and on the way, flips the bolt release. I’ve never needed to use the forward assist mechanism, because I’ve always been meticulous with the ARs I’ve fired. On the other hand, a gun like the F2000 is either "Grab magazine with lefthand, put away, put in new magazine " or “Left, on the way back, locks bolt, grabs magazine, puts new magazine in, releases bolt on the way back to position” (you can see the charging handle, [here](http://en.wikipedia.org/wiki/High_Standard_Model_10), on the lefthand side, towards the front of the firearm). The F2000 also uses a piston system, like a lot of other evil black rifles, which doesn’t dump burnt material into the action of the firearm. It also has a “Fouled” or “low-charge” setting, where the gun will still feed if it’s heavily fouled or the rounds are undercharged. I’m using the FS2000 here, because I own one and I know the gun well enough to speak about it where I don’t know the AUG or H&K action designs, although my understanding is they’re similar. I also have a pretty good understanding of the SCAR-L/SCAR-H, which have superior actions to the AR (in that they’re piston systems). The real fact of the matter is that the AR is a good design, and the US military is heavily invested in it, so they’re not likely to switch (en masse) to any other firearm unless it offers significant, measurable advantages to the AR platform. Was direct impingement worth it? In itself, probably not. But, Stoner designed a good gun, and despite the drawback of DI, the gun itself was still worth it – massively more so at the time. Again, IMHO. ---
**Author:** ![cerberus](https://avatars.discourse-cdn.com/v4/letter/c/71e660/32.png) [@cerberus](https://boards.straightdope.com/u/cerberus)\ **Post date:** [July 27, 2010, 2:07am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/3 "2010-07-27T02:07:11Z")
My AR10 doesn’t require a forward assist…isn’t the AR10 just a big cousin of the AR15? ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [July 27, 2010, 2:12am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/4 "2010-07-27T02:12:27Z")
The bold carrier of the AR-15/M-16 slides all the way past the ejection port. (The bolt itself can be seen at the aft end of the ejection port when the bolt carrier is back.) In order to have the charging handle on the bolt carrier, there would have to be a slot behind the ejection port. ISTM that that would risk getting debris into a mechanism that doesn’t work well when there’s junk in it. As it is, the bolt carrier provides more-or-less adequate protection when it’s in battery and the port cover is open. Another Stoner design, the AR-18/AR-180 uses a piston as described in post #2. I have one, and it’s a bit ‘looser’ than an AR-15 (which I also have). The charging handle is attached to the bolt and reciprocates with it. There is, therefore, a slot for it in the receiver. There’s also a spring-loaded cover. Interestingly, we used to have posters here named **Eugene Stoner** and **Kalashnikov**. I always got a chuckle out of that. But they’ve both been banned. ---
**Author:** ![Johnny\_L.A](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johnny_l.a/32/1084_2.png) [@Johnny\_L.A](https://boards.straightdope.com/u/Johnny_L.A)\ **Post date:** [July 27, 2010, 2:14am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/5 "2010-07-27T02:14:17Z")
> [@cerberus](#): > > My AR10 doesn’t require a forward assist…isn’t the AR10 just a big cousin of the AR15? The AR-10 was a precursor to the AR-15. The original AR-15/M-16 also did not have a forward assist. My 1979 SP-serial number Colt AR-15 does not have forward assist. ---
**Author:** ![Todderbob](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@Todderbob](https://boards.straightdope.com/u/Todderbob)\ **Post date:** [July 27, 2010, 2:41am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/6 "2010-07-27T02:41:08Z")
They added the forward assist, iirc, to help with combat jams, so you didn’t have to pull the bolt in order to close the action, only as a last resort. It wasn’t there originally, and was never intended to be used every time the gun was loaded. ---
**Author:** ![AmosMoses](https://avatars.discourse-cdn.com/v4/letter/a/57b2e6/32.png) [@AmosMoses](https://boards.straightdope.com/u/AmosMoses)\ **Post date:** [July 27, 2010, 2:45am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/7 "2010-07-27T02:45:24Z")
> [@Johnny\_L.A](#): > > > [@cerberus](#): > > > > My AR10 doesn’t require a forward assist…isn’t the AR10 just a big cousin of the AR15? > > The AR-10 was a precursor to the AR-15. The original AR-15/M-16 also did not have a forward assist. My 1979 SP-serial number Colt AR-15 does not have forward assist. Correct, of course, but the original, especially with the particular ammo the military originally picked for it, could have really used a forward assist!! Also, just an aside, here - there’s another possible reason that his “AR-10” may not have a forward assist…it may well be that he’s referring to a weapon like some of DPMS’s .308 NATO rifles, especially the SS bull barrel rifles. Now, he may not be, and I am obviously not disputing your answers in any way at all. I just know that many of these rifles rolled out in the last couple/few years, and although I don’t, I have heard many people refer to them as “AR-10s” simply due to the caliber. These, like DPMS’s “Sportical” line, simply do not have a forward assist, nor a dust cover. In fact, I have one myself, as well as a Sportical in 5.56. ---
**Author:** ![JerseyMarine2092](https://avatars.discourse-cdn.com/v4/letter/j/8491ac/32.png) [@JerseyMarine2092](https://boards.straightdope.com/u/JerseyMarine2092)\ **Post date:** [July 27, 2010, 2:55am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/8 "2010-07-27T02:55:36Z")
> [@MichaelEmouse](#): > > Was anyone else trained to take the magazines out with the left hand, pull the T-bar with the left, push the forward assist with the right hand and then close the port cover with the left hand? This isn’t gonna to make me look good. 😛 I can’t remember what I was _trained_ anymore, and this might just be a decade’s worth of bad habit. But I perform loading/reloading entirely with my left (ie non-shooting) hand. My grip with my left hand cups the rifle where the hand guard/barrel meets the magazine well. This puts the magazine release within easy release of my index finger. I bring my hand down as I hit the mag release (and keeping my weapon on target) catch the mag, put the fresh one in, and hit the bolt release with my left thumb. I also put the majority of my loaded magazines on my shooting side so I can easily reach them. Miming the actions right now, I could probably do it with my right hand too, but I’m going to spend a bit more time fumbling for my fresh magazine. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [July 27, 2010, 5:16am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/9 "2010-07-27T05:16:22Z")
Wait - is the forward assist that weird lever on the right of the weapon that no-one ever uses? I’ve never understood why it was there, and neither did any of my instructors. ---
**Author:** ![Todderbob](https://avatars.discourse-cdn.com/v4/letter/t/e47774/32.png) [@Todderbob](https://boards.straightdope.com/u/Todderbob)\ **Post date:** [July 27, 2010, 5:22am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/10 "2010-07-27T05:22:45Z")
> [@Alessan](#): > > Wait - is the forward assist that weird lever on the right of the weapon that no-one ever uses? I’ve never understood why it was there, and neither did any of my instructors. That’s the one, and now you know. ---
**Author:** ![opmike](https://avatars.discourse-cdn.com/v4/letter/o/9d8465/32.png) [@opmike](https://boards.straightdope.com/u/opmike)\ **Post date:** [July 27, 2010, 6:16am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/11 "2010-07-27T06:16:38Z")
One advantage to having it, is to confirm lock up after performing a press check or otherwise only partially moving the bolt carrier group rearward (such as “breaking the seal” to allow water to drain from your barrel after submersion). Sometimes, only partially pulling the charging handle to the rear, and releasing it doesn’t supply enough force to allow for the gun to return to battery. Giving the forward assist a few taps can ensure proper lockup. Some guys I know also have a habit of giving their forward assists a few taps before performing an entry into a building or imminent engagement to be absolutely sure that some piece of gear, clothing, etc. didn’t slightly bump the rifle out of battery, and that their rifles will be ready to go. And while forcing a stubborn round into the chamber is generally bad practice, sometimes you don’t really have a choice. I know of at least two incidents where such a thing was necessary, and potentially saved the user’s life. You’ll probably never need to use it, but you’ll be damned happy it’s there in the rare chance it does arise. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [July 27, 2010, 6:30am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/12 "2010-07-27T06:30:45Z")
> [@MichaelEmouse](#): > > Was anyone else trained to take the magazines out with the left hand, pull the T-bar with the left, push the forward assist with the right hand and then close the port cover with the left hand? No competent instructor anywhere on the planet would _ever_ teach this technique. It makes absolutely zero sense. Though you didn’t directly state that you were taught to reload in this manner, it was implied by this sentence. Either you misremembered something, or your instructors are baffoons. Think about it for a second. If you are reloading, your weapon will be in one of two states: 1. Round in the chamber (bolt forward) and a less than full magazine. or, 2. Empty magazine, no round chambered (bolt to locked to the rear) Neither one of those situations require you to pull back on the charging handle. So who in their right mind would teach you to pull back on the charging handle to reload? Either the bolt is forward, but since a round is chambered you don’t want to pull the handle or you will eject a good round. Or the bolt is already to the rear, in which case pulling back the charging handle does nothing at all! ---
**Author:** ![opmike](https://avatars.discourse-cdn.com/v4/letter/o/9d8465/32.png) [@opmike](https://boards.straightdope.com/u/opmike)\ **Post date:** [July 27, 2010, 6:39am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/13 "2010-07-27T06:39:34Z")
> [@](#): > > Or the bolt is already to the rear, in which case pulling back the charging handle does nothing at all! If the bolt is locked to the rear, and a full magazine has been inserted, pulling fully rearward on the charging handle and releasing it will disengage the bolt catch and chamber a round. Similar to how some people will, at slide lock for a pistol, pull and release the slide instead of using the slide catch/release. With handguns, I think this is a good idea for a number of reasons. On an AR, not so much. Pulling back on the charging handle runs the risk of you accidentally riding the charging handle forward, which could result in a round not fully seating in the chamber. It is also slower than simply depressing the bolt catch, and a little more awkward. ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [July 27, 2010, 7:00am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/14 "2010-07-27T07:00:54Z")
> [@opmike](#): > > If the bolt is locked to the rear, and a full magazine has been inserted, pulling fully rearward on the charging handle and releasing it will disengage the bolt catch and chamber a round. Yea, I guess you are right. And I hadn’t considered the fact that once you superfluously pull the charging handle back–99% of the motion will be under zero resistance and perform no function–that last 1% of travel will release the bolt. But that is why there is a bolt release which is designed to release the bolt. Pulling back the charging handle in this situation is idiotic. ---
**Author:** ![Nametag](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nametag/32/406_2.png) [@Nametag](https://boards.straightdope.com/u/Nametag)\ **Post date:** [July 27, 2010, 7:35am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/15 "2010-07-27T07:35:17Z")
> [@Bear\_Nenno](#): > > > [@MichaelEmouse](#): > > > > Was anyone else trained to take the magazines out with the left hand, pull the T-bar with the left, push the forward assist with the right hand and then close the port cover with the left hand? > > No competent instructor anywhere on the planet would _ever_ teach this technique. It makes absolutely zero sense. Though you didn’t directly state that you were taught to reload in this manner, it was implied by this sentence. Either you misremembered something, or your instructors are baffoons. Is a baffoon a cross between a baboon and a buffoon? ---
**Author:** ![Bear\_Nenno](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bear_nenno/32/3358_2.png) [@Bear\_Nenno](https://boards.straightdope.com/u/Bear_Nenno)\ **Post date:** [July 27, 2010, 9:12am UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/16 "2010-07-27T09:12:53Z")
> [@](#): > > Is a baffoon a cross between a baboon and a buffoon? I hate you. ---
**Author:** ![MichaelEmouse](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/michaelemouse/32/101_2.png) [@MichaelEmouse](https://boards.straightdope.com/u/MichaelEmouse)\ **Post date:** [July 27, 2010, 2:30pm UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/17 "2010-07-27T14:30:49Z")
> [@Bear\_Nenno](#): > > No competent instructor anywhere on the planet would _ever_ teach this technique. It makes absolutely zero sense. Though you didn’t directly state that you were taught to reload in this manner, it was implied by this sentence. Either you misremembered something, or your instructors are baffoons. Both are possible. Here’s how I remember being instructed to switch barrels on an M-249 and an M-240: Pull charging handle to the back. Open cover. Swipe rounds belt out of the weapon. Close cover. Pull trigger. Pull charging handle to the back. Engage safety. Press barrel release. Quarter turn of the barrel and pull it out. Insert new barrel and stop pressing on barrel release. Disengage safety. Grasp charging handle while pulling trigger to gently bring bolt group forward. Open cover. Put rounds belt inside weapon. Close cover. Bring charging handle to the back. Now ready to fire. It seems to me a few movements could be omitted without significantly affecting safety. Pulling the trigger after having swiped the rounds out seems to ignore the fact that the M-249 and M-240 are open bolt weapons and that therefore, if you swipe the belt out of the weapon, pulling the trigger will do nothing since there are no more rounds in it. Or perhaps there’s a good reason to do it and I just don’t know enough about MGs. ---
**Author:** ![cerberus](https://avatars.discourse-cdn.com/v4/letter/c/71e660/32.png) [@cerberus](https://boards.straightdope.com/u/cerberus)\ **Post date:** [July 27, 2010, 7:30pm UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/18 "2010-07-27T19:30:28Z")
My AR-10 is an A2 variant, an actual Armalite rifle. Oddly enough, the rear part of the upper assembly has a bulge where a FA would normally reside. ---
**Author:** ![JerseyMarine2092](https://avatars.discourse-cdn.com/v4/letter/j/8491ac/32.png) [@JerseyMarine2092](https://boards.straightdope.com/u/JerseyMarine2092)\ **Post date:** [July 27, 2010, 8:20pm UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/19 "2010-07-27T20:20:11Z")
> [@opmike](#): > > > [@](#): > > > > Or the bolt is already to the rear, in which case pulling back the charging handle does nothing at all! > > If the bolt is locked to the rear, and a full magazine has been inserted, pulling fully rearward on the charging handle and releasing it will disengage the bolt catch and chamber a round. Similar to how some people will, at slide lock for a pistol, pull and release the slide instead of using the slide catch/release. With handguns, I think this is a good idea for a number of reasons. On an AR, not so much. > > Pulling back on the charging handle runs the risk of you accidentally riding the charging handle forward, which could result in a round not fully seating in the chamber. It is also slower than simply depressing the bolt catch, and a little more awkward. It seems like a wasted motion when you can just hit the receiver hard enough to send the bolt home. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [July 27, 2010, 8:28pm UTC](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134/20 "2010-07-27T20:28:50Z")
> [@MichaelEmouse](#): > > Both are possible. Here’s how I remember being instructed to switch barrels on an M-249 and an M-240: > > Pull charging handle to the back. Open cover. Swipe rounds belt out of the weapon. Close cover. Pull trigger. Pull charging handle to the back. Engage safety. Press barrel release. Quarter turn of the barrel and pull it out. Insert new barrel and stop pressing on barrel release. Disengage safety. Grasp charging handle while pulling trigger to gently bring bolt group forward. Open cover. Put rounds belt inside weapon. Close cover. Bring charging handle to the back. > > Now ready to fire. Are you sure about that? Because that way, you have a situation in whcih a belt is in the weapon and the safety isn’t on. Sure, the bolt is forward, but still - you shouldn’t have a loaded weapon with the safety off unless you’re pointing at the target. The final stage should be: pull back charging handle. Engage safety. Open cover. Put rounds belt inside weapon. Close cover. Disengage safety. Aim. Fire. [Next page](https://boards.straightdope.com/t/m-16-ar-15-operating-mechanism/548134.md?page=2)