Was looking at one of my ar15's last night and was noticing that the M4 handguards had some rotational play to them.  Now they have been this way for some time and I never gave it much thought since I have always had a little play with the same type of handguards on my other carbine.  Well last night I was paying a little more attention and noticed that the barrel nut was moving with the handguard as I rotated it back and forth.  Seeing that the barrel nut was moving, I put one hand on my upper and the other on the front sight base and tried to see if I would get any rotational play between the barrel and upper.  I think I detected a small amount of play, but it was so small I could have been imagining it, though.

My question is, if I don't tighten up the barrel nut before taking it out to shoot again will I have to worry about breaking a bolt or anything like that?  I don't have the tools right now to re-torque the nut, but I was planning on buying them anyway, so I can do it down the road.  But I may want to take this rifle out to shoot before I do get the tools and was wondering if it was wise.  

I realize that I may have some accuracy issues and this would probably explain the problem I was having in trying to sight in a new scope and seeming to have wandering zero issues.  However, since the bolt locks up in the barrel extension, I would imagine that there wouldn't be any way to damage my rifle if there was a minor amount of play between my upper and barrel.  I think that this condition has existed for some time and I haven't had any real accuracy issues shooting irons or a red dot sight, just issues when I was shooting with the scope and even then it was somewhat minor.

I guess the reason I am dragging my foot in wanting to re-torque the barrel nut is that I will probably have to re-zero all my sights for the rifle and it is getting cold out and would like to wait to do this until next spring.  I would prefer to sight in the rifle at a more median yearly temp so that the variation in bullet POI would be reduced during hot and cold spells.

Hi Jason,

I would not shoot the rifle until it is tightened, I am 99% sure your zeros will be relatively close. Even without the torque wrench I would be willing to bet one more tooth over is probably sufficiant (again, best case is with torque wrench but as you stated that is down the road) even if the barrel was to push far enough from the receiver I doubt you would have some headspace problems from the nature of the roatating bolt design...then again???(I do feel accuracy should suffer)When dealing with thousands of PSI of white hot gas I say safe than sorry.

Robert

 

Some hand guard play is normal. The delta ring is retained by only a spring, and is kept from rotating by the gas tube as it goes into the receiver.

 

The delta ring (outer sleeve) was rotating. The barrel nut is the star nut inside the delta ring, and chances are that it is still tight.  




If the barrel nut were loose, the barrel would slip in the upper receiver (both ways).  The barrel nut is held in place by torque of 35lbs, and the gas tube that goes threw the spine of the nut.

If you really want to check the barrel nut, pull the hand guards, and see if it spins (star nut inside the delta rings).

As for a wandering zero (POI), if you have been changing ammo (different lots or brands), this will cause the different points of impact, and is the reason that most of us buy ammo by the 1K lots.

 This problem is independent of the sights (front sight canting/rotating forth), chances are either you have been changing ammo, or the scope is not holding a zero.

I had this exact same thing happen to me on a factory Colt AR-15A2 model 6500.  After shooting a few thousand rounds through it in 3 or 4 years, the barrel nut got a little wiggly.  I have no idea how long it was like that before I fixed it, but it was probably loose for at least a few shooting sessions.





Don't worry about it - go ahead and shoot.  The upper receiver is not a stressed member, so there's no chance of blowing up.  It's not that big of a deal.  If the notch in your upper receiver is loose, you may notice your zero wander back and forth a few inches in windage, but that's all.



Forget the torque wrench and everything the Torque Nazis on this board tell you.  Read [url=http://www.ar15.com/forums/topic.html?b=3&f=4&t=173151]this thread on Build it Yourself[/url] for the tools and all the information you need under [b]The Famous Homo Erectus Barrel Mounting Method[/b] and you'll have no problems.  Buy an action block and combo wrench and you're all set.



I think you're going to find that your zero will be suprisingly stable, so don't woory about it shifting much, if at all, when you retighten the barrel nut.

When I finally got around to fixing my Colt, I merely removed the gas tube and cranked the barrel nut over to the next gas tube notch and it's been shooting fine for almost 2 decades now.

And I never used a torque wrench.  [:D]

Thanks for the replies guys.  Just to clarify, the barrel nut was actually moving, not just the delta ring.  I could see the notch in the barrel nut making contact with the gas tube as I twisted the handguard.  The fact that the barrel wasn't moving a whole lot may just be due to the index pin having a fairly tight fit in the upper, who knows.  I plan on doing some major overhauling on this rifle down the road such as installing a free float handguard, so maybe I will just do it now instead of putting it off.  In the meantime, I suppose this will give me a good reason to pull some of my other rifles out of the safe and shoot them instead, since they just sit in their collecting dust as of now.

Nazis? Nice. Would you care to show where anyone of consequence on this board has beat the "torque wrench drum" H_E? The only reference I can think of is in the FAQ and that's a link to one of Doublefeed's posts.

jason_h,

Buy the receiver block (having a vise helps) and get an armorers wrench, any style is good enough for sporadic work, and tighten the nut. Remove the handguards, bolt carrier and the gas tube, block up the receiver and turn the nut until it's tight, continue turning it until the teeth are properly aligned. Sometimes you may have to loosen the retighten the nut to get the teeth to align. On a really bad day it may be easier to change out the barrel nut but, thankfully, those days are pretty rare.
Reinstall the gas tube, strip the bolt out of the bolt carrier assembly and use the BC to make sure that the gas tube is properly aligned. Adjust the gas tube if it's not aligned. Reassemble the bolt carrier and perform the drop shut test. Reassemble the upper and function check. You should be good to go.

If you don't have the tools it may be wise to remove the handguards and gas tube and check to see how loose the barrel nut is. You may be able to "tighten" it enough by hand to get you through the winter.

Your wandering zero may be related to your scope and/or mount. I've seen more than a few loose barrels and very few showed that symptom. That may be more because of the skills of the shooter or their style of shooting tho. [;D]

Yes, a tight fit between the alignment pin and its notch will keep the barrel aligned. A friend of mine brought his PWA 20" A1 out to the house a few months ago. He zeroed it at 25 metres and checked the POI at 170 metres. He came back out (having shot the rifle several times in the intervening months) and he shot it at 300 metres. All POI and groups were good to go. On the way back to the house he asked about his loose (rotationally) handguards. Post shooting inspection showed that the barrel nut was loose, not even hand tight.[shock]

It's just a term - like Headspace Weenie. I wasn't referring to anyone in particular, so don't protest [i]too[/i] much.  [:D]  



[url=http://www.ar15.com/forums/topic.html?b=3&f=4&t=171456]Here's one.[/url]  Hey, that's you, Tweak! [url=http://www.ar15.com/forums/topic.html?b=3&f=118&t=175041]Here's another[/url] where a member is extolling the virtues of torque wrenches.

I don't think a week goes by where I don't see someone post about how you have to smear magic grease on the threads, tighten and loosen three times, and use a torque wrench on the barrel nut for an absolute minimum of 35 ft-lbs.  Granted, most people who do aren't what you would call "anyone of consequence," but noobs who wander onto ARF.com looking for advice on their first build don't know any better and are prone to listen to the "Torque Nazis" who repeatedly parrot passages out of the TM.

As you're painfully aware of [:)], I usually hang out on "Build it Yourself," but since you started to show up over there recently I decided to see what "Troubleshooting" was like.   I'd search for more examples, but my search capabilities are limited (and I absolutely refuse to contribute money until a little matter with Stryker is resolved), so you'll just have to wait until this subject crops up again so I can say "See, here's another one."  [:D]

One of the reasons I speak out against the TNs is I've seen too many new builders have problems, skin knuckles, and sometimes ruin parts crankng down on barrel nuts trying to obtain some magical torque value.  I'd rather try to educate them on exactly how an AR operates and the tiny amount of stress that an upper actually is subjected too, rather than have them follow a TM that was written for troops who literally are taught to walk, tie their shoes, and use the latrine by military pubs.

It's just one single nut, and it's not under any firing stress, so I don't see why tightening it should be such a big deal.  I'm glad to see we agree.  [:D]

[Edited to ficks speling misteaks.]

Welcome to the trouble-shooting forum.  

What you find out around here is that we spend 99% of the time trouble-shooting Non-Colt rifle.  Which means that all kinds of parts on the troubled rifles maybe out of spec.  Granted that your "NO torque wrench idea" may work on a Colt rifle were the parts are checked no less than three times before they leaving the factory, but on rifles that are built out of unknown origin parts, not using a torque wrench on the barrel nut may cause some serious problems.  

The biggest problem is the upper barrel socket/threads start to stretch at around 100Lbs, and the threads will strip/crack a just less than 140Lbs.  As tweak has pointed out, some barrel nuts are just junk, and require replacement.  Other problems are when the upper barrel socket face/barrel extension lip is out of spec, which the upper barrel socket face needs to be relieved/faced in order to get to the next spine space without destroying the receiver (over torque).

Point blank, the TM gives torque values ranges for each nut/screw on the rifle, and the purpose is to prevent the destruction of parts, due to over torque.    

To suggest that someone who has never tighten a barrel on an AR-15 before, do so blindly without a torque wrench on what may be “out of spec parts”, is a disaster waiting to happen.  

Yep, and the initial poster asked what the torque [b]limit[/b] was. I answered that it is 80 ft/lbs, nothing more. Torque in excess of 90 ft lbs will usually shear teeth off of the barrel nut therefore knowing what the upper limit is can be useful.

Later on, in that thread, I said:





As with your previous example, the poster is not a noted member of the board and the thread is not on this (Troubleshooting) board.



And I see weekly references to tumbling bullets, shooting to wound, and other nonsense. I haven't made it my personal mission to eradicate those falsehoods. Those that want to climb the mountain will find their own path.



That is strange, those are the very same reasons given for putting torque limits on parts.



It's not a big deal, except when the nuts come loose from not being tightened enough or tightened improperly.  I have only used a torque wrench once or twice (both times at OAI) and then only to quantify "tight" for my own edification.

You don't have to convince me that the TMs are full of errors, so are the FMs, TBs, media of all kinds and, even, the www. One has only to look at the torque values for the carrier key screws to know something is wrong. Tight is tight. Explaining what "tight" is to a person with no experience is a little more difficult.

Funny thing is this is a Colt, at MT6400C to be exact.  It's one of the early production ones with "Colt's Manufacturing" stamped on the side of the receiver insteand of "Colt Defense."  It doesn't have the T-numbered, M4 stamped upper or a MPC marked bolt.  The bolt is kind of scary because it doesn't even have the stress relief indentations behind the bolt lugs.  The rails on the upper receiver are out of spec as well and it looks like someone got carried away with a dremel tool on it.  Everything else on it is spec, its just the upper receiver and bolt that is not.  It is pretty obvious that not much concern was put into building this rifle so you knows how tightening down the barrel nut will go.  This was my first Colt rifle so I was not aware of what all to look for, oh well, live and learn.

I can't complain too much, though, since it has been completely reliable.  As Tweak mentioned, the wandering zero issue may be something other than the barrel nut, like the scope, mount, or the fact that the rails are improperly machined (grrr).  Thinking of getting a SIR, so that I can have a good platform for attaching optics, just hope the rails are close enough to spec that the SIR will fit.

I realize that Colt does make good stuff, just not for us lowly civilians.  I don't know, maybe I should just replace the bolt and upper with spec parts and keep the old parts for spares.

I'd send that rifle back to Colt and ask for a new one, that just plain sucks!!! What happend to Colt QC That day. For what you paid for that rifle Colt should have no problem taking it off your hands and giving you a brand NEW M4. I haven't even heard of Bushmaster puting out anything that out of spec. I'm not bashing Colt everyone has there off days but, DAMMM!!!      

Edited to add, I think it's close enough to christmas for them to give you a new one as a present[:)]

You have heard of purple BFIs and their cockeyed barrels right 556Cliff? [;D]

jason_h,

Where did you get this rifle?

Yes I have heard of Bushmasters problems. Mine is ever so slightley canted and I can't stand it!!! so I'm going to buy the tools and fix it myself, and when if the ban ends I'm going to put a preban 20"A2 barrel on it.[;)]

It suprised me though that Colt put out something like that.  

TOOLS = Leather mallet.

METHOD = Hold the upper receiver with one hand, and then strike the front sight tower just above the barrel.  This will slip the entire barrel in the upper barrel socket, and fix your canted front sight.  If you’re real good, you can drift the barrel to the correct index for the rifle to be zeroed with the rear peep aperture center mark perfectly centered on the sight housing center mark.

I'm interested to hear the lineage of the piece. I've seen plenty (more than 20 in one day) of phony "Colt M4s". All were slapped together from available parts, some Colt, some clone, bolted to Colt (any model) lowers and sold as Colt factory guns.

Dano523, thanks for the info, how hard do I have to hit it?

Tweak, it does kind of sound like a bad dealer slaped it together.

Well jason, where did you get this thing?    

Eeeeek!!!!  [BD]



I run into canted sights all the time, but take a slightly more gentle approach to fix it:

What I do is spin off the barrel nut and check the fit of the barrel locating pin in the upper receiver notch.  To bring the front sight base up straight, take a jeweler's file and slowly open up the notch in the direction you want the front sight to move.  Work slowly, a few strokes will make a visible difference at the front sight.

Lining up the sights is easy.  Brownells used to sell a really neato rod that fits in your carry handle and points to the front sight post, but I'm [b]way[/b] to cheap to buy one of those.  I've tried stuff like tying a thread to the front sight post and running it back through the rear sight aperature.  But I've also gotten good results by just plain eyeballing it by sighting down the carry handle to see if the front looks straight.  This is usually good within 5 clicks of windage if you're careful.

Once the notch is opened up to bring the front sight up straight, you need to tighten up the "loose side" of the notch with a hammer and punch so the barrel won't move when you tighten the barrel nut.  With the barrel in place, very lightly (it doesn't take much!!) peen down the threaded area next to the barrel pin.  (The barrel extension acts like a little anvil.) You'll find that you barely have to tap it at all to tighten up the notch.

Now that the barrel is straight and can't shift, screw the barrel nut back on, install the gas tube and handguards and you're done!


[Edited to ficks speling misteaks.]

Thanks for the info, but it,s not the windage thats bothering me, it's onley off by about 5 clicks, it's that my gas tube is slightly canted. So instead of bending the gas tube I'm going to use a barrel wrench and move the barrel nut, the tube is hitting one side of the notch on the nut, I'm just going to move it enough until it's off. Then it should be lined up with the carrier key Right?        

I use a short (2"-3") section of an old gas tube as an alignment tool.  Stick the tube in the bolt carrier key, and the push the bolt carrier into the upper receiver while tightening the barrel nut.  The tube will stick out the hole and will keep the circlip, weld spring, and delta ring indexed, and will pop through the barrel nut when the notch lines up.  You can slide the bolt carrier back and forth to check the barrel nut alignment.

Homo_Erectus,  

When I install a barrel, I use a sight bar tool, so I know that the front sight is indexed with the carry handle.  But, just because the tower is indexed with the handle, doesn't mean that the front sight is looking where the barrel is putting the round down range.

Trust me, When I had a lot more time on my hands, I used to screw around with trying to get the front sight just right (Re-installs to have the rear sight dead center @ zero), but found that on a fixed front sight tower, a leather mallet makes the job a few seconds, verse hours of wasted time.

I've checked the Brownells site but can't find that site idnexing tool anywere. got a link. Since I'm new at this I want every tool to help me out.  
 
Also if your windage is off even just a little bit, like two three, five clicks, does that mean your indexing pin is bent, or is there a small amount of play in between the pin slot and the pin.

Thanks for answering my questions.[:)]        

Either/or on the barrel extension pin/upper barrel socket.

Brownells used to sell the bar, but haven't seen it listed in for few catalogs.

Give me a chance, and I will see if I can find you a source for the bar ($65).  

Also, like a muzzle laser, it only going to get you close to the correct front sight index, you will still need to fine tune the front sight under fire, which brings up back to the tweaking with a leather mallet, or stripping out the gas tube and re-installing the barrel to move it a fraction of a inch.  Unless you have a private firing range at the shop, the leather mallet makes short work out of fine-tuning away from the shop.

Thanks Dano523,

[WOW]65$ is alot of money!!!    

Rifle Front Sight Alignment Tool
EX0114 $58.00

[url]www.armalite.com[/url]

Go under catalog, then tools.  It's down about middle of page on the left.

Thanks Dano!

Hello Jason,
 Here originally from Pawnee.
 I also have the MT6400C. Have you had any problem with the Mikulek compensator loose or blowing off? Is it mounted on with roll or solid pins?
Thanks, Jason!
Randy

I removed the comp after I got it, since I didn't need it and it made the barrel longer than it needed to be.  Just have a bare muzzle now.  It was held on with the hollow roll pins.

Seems as though I remember a few accounts of rough looking MT6400C's when they first came out.  Read a post from one guy that said his had substandard parts in his as well, ended up selling the upper and keeping the lower.  Also heard of others that have the same rifle and there upper doesn't have the M4 markings either.

As far as the lineage of this rifle, a friend of mine that has an FFL, got it from a distributor, can't remember the distributor's name though (maybe Jerrys out of KC?).  It was the first one he ever got in, and supposedly the first one the distributor ever got in as well.  He showed me the invoice for it, and it came in the right box with all the papers and accesories.  The front sight, carrier, and barrel are all properly marked.  Serial number is in the 300 range with "Civilian M4 Carbine" marked on the side of the mag well.

I am certain this rifle came this way from the factory, and I am not surprised about its shortcomings.  Like I said, I have heard other accounts of the same type of problems with the early production MT6400C's.  It wouldn't surprise me if the whole reason Colt originally decided to put out this model, was that they had a bunch of slightly out-of-spec parts they couldn't in good conscience put on their Mil/LEO rifles, so they decided to pawn them off on their civilian customers instead.

I could call Colt about it, but we all know what the response will be.  They may have me send it in, then I will wait 6 months, then I will get the same exact rifle back.  Afterall, the rifle does function, and the carry handle, aimpoint mount, and ARMS #35QD mount all do fit the rail, so I doubt they would say that my rifle would need warranty work.  The problem with the rail is that its edges are not machined evenly from front to back.  On the right side, the wedged shape part of the rail is wider at front than the rear, and on the left side its the same thing, only reversed so the wider part is at the rear.  Kind of hard to explain, wish I had a camera on hand.  Thing is, the rail is close enough to spec that it works on a basic level, just doesn't work as well as one would hope it would.

As for the bolt, will keep an eye on the barrel lugs and if I start to see any signs of them being overstressed, will just replace it.  It's not like all the lugs are going to fail at the same time, so I don't think there is any safety concerns.

Not really pissed off at Colt since I did have a chance to look the rifle over before I bought it, more pissed at myself for buying it.  Plus, this is nothing new from them, we have all heard the horror stories about M1911's, Pythons, stuff that comes out of their custom shop, etc.

Anyway, thanks for all the replies, this thread has sort of spun off in three different directions, but it's all good.

I'd still recommend you contact them or one of their contract service centers near to you. The rifle does have a warranty on it.

Yep I'd call Colt and bitch'em out! They can't let us feed off their out of spec garbage. Even though this is probably a rare thing that happend, someone should still let them know.  

Coincidentally, I'm experiencing the same exact issue with my upper / barrel. But the rotational 'play' is definitely noticeable on mine....I'd say at least 1 or 2 mm of movement.
Glad I caught this post. ARFcom to the rescue............................again!!

jason_h,

On conversation with a knowledgeable source I, again, recommend that you return the rifle to Colt. We (the source and I) both suspect that parts may be been removed from your rifle somewhere between the factory and you. This is not unheard of in the industry.

Final follow up to the preceeding discussion.  Unfortuantely warranty service is not an option since I started modifying the rifle about a year ago.  First I removed the brake, then later shortened the stock, and currently have broken down the upper into its individual parts so that a KAC FF RAS can be installed.  I doubt they would just let me send in the offending parts by themselves for replacement, well that and I have long since voided the warranty, heh.  

Anyway the two parts that were questionable were the upper receiver and the bolt.  First of all, I need to admit to being a dumbass for making some comments in error.  The bolt is not as bad as I orginally thought it was.  It does have the relief indentations behind the lugs.  I had just not noticed them in the past and when I checked the bolt last before posting it was covered in fouling and couldn't see them.  Yes I am an idiot, I should have looked closer.  That said, the marking on the bolt consists of a "C" sort of pinged into the side were the "MPC" would normally be.  The extractor also has a "C" marked on it on the underside and has the black insert and heavy extractor spring installed.  Not sure if I should be worried about the lack of the "MP" in front of the "C" since I would assume they magnaflux all the bolts together, no reason to only do some of them.  But then again, reason doesn't always seem to rule the day there in Hartford, CT.  The bolt hasn't broke yet, so I figure its good to go.  I have a spare "MPC" bolt on hand though, if it does decide to give me lip.

As for the upper, my original gripes still stand.  The finish is poor on the outside, lacks the T-numbering, and the machining on the rail looks sort of funky.  I also failed to mention that the extended ramps were ground into the receiver after it was anodized, so they are bare aluminum.  That is about it as far as issues with it.  On the bright side, the machining on the inside of the upper is good.  

I broke out the calipers to take some readings on the rail.  Long story short, some dimensions were non-uniform, but I am not certain those dimension really matter.  After all I have had no noticable problems in removing my red dot sight and irons and having the zero change.  Just problems with the scope and I still have some other variables to rule out there before I can be certain what is up.

As for whether the receiver is Colt or not, the upper does have "C" and "AF" forged into it on the right side so I am pretty sure this part is Colt.  Plus it would make no sense why someone would totally disassemble a upper, just to change out the receiver.

Maybe I should count the receiver problems as a blessing since now I won't be tempted to baby it.  This means I can run the carrier near dry, use the port door as it was intended, and sling shot the charging handle with ease of conscience.  If the upper wears out prematurely, all the more reason to replace it with a good one.  Maybe by then, LMT uppers will be a dime a dozen, and I can pick one of them up on the cheap.  Well one can dream anyway.

Oh and as to the orginial question that started off this thread, guess I will be tightening the barrel nut before it goes out again.  Kind of have too now. [:)]

Edited to add that the reason there was not much rotational play when the nut was loose was that the notch in the receiver is almost a near perfect fit for the index pin.  I guess that's one more reason to love my upper receiver. [;)]