AR-15 TECHNICAL INFORMATIONEXCHANGE
AR-15 TECHNICAL INFORMATIONEXCHANGE
|Now before youtear apart your perfectly good rifle, you might want to read this entirearticle, including the troubleshooting section to see what you are gettingyourself into. They don't call it "troubleshooting" for nothing.Of the major AR-15parts and accessory distributors, I've found thatBrownellsis probably the best source. Therefore, I've already looked up and addedthe item number for some of the tools and parts you'll need. Below is alist of tools and parts for this project. Some are "required" and someare "recommended". I managed to get by with just the required tools. Iincluded a hacksaw, but that was due to the configuration of my rifle andthe configuration I wanted to end up with. Take a hard look at your projectbefore you decide which tools you'll need.|
One decision youneed to make before you get started is whether you will be installing anew gas block, like one of the rail types described in this article, orthe original gas block. The reason for this is the original gas block onthis rifle configuration has a sight post on it. This will be removed fromthe gas block. (See details below.)
Armorers Wrench - Brownells item # 231-000-007
Taper Pin Starter- Brownells item # 827-530-320
Heavy Hammer(about 3 lbs)
Wood or plasticspacing blocks
Receiver ActionBlock - Brownells item # 702-003-015
Bench Vise -Medium to large
Precision calipersor straight edge
Tools - Recommended
Wooden malletor plastic hammer
Roll pin punch-Brownells item # 230-112-105
Strap wrench(For one-piece handguard installation) Â– Brownells item # 382-100-015
DPMS Armorer'sWrench Â– Brownells item # 231-000-007
Free float TubeWrench (For two piece handguard installation) Â– Brownells item # 231-015-023
Gas tube wrench- Brownells # 133-100-015
Handguard removaltool - Brownells item # 100-000-438
Lower receivervise block - Brownells item # 702-004-015
*Hacksaw - Dependenton configuration. - See text
*Fine to mediumfile
*Birchwood Casey"Alumablack" - Dependent on configuration. - See text
(* For front post sight modification only - see textbelow)
Parts - Required
Handguard of yourchoice, one or two piece
Parts - Recommended
Front sight taperpins - two (Can use old pins if not damaged during removal)
Gas block - Ofyour choice (if you are not re-using old block) (Checkbarrel diameter before ordering)
Gas tube - Incase the old one is damaged in the process
Gas tube retainingpin (in case the old one is damaged in the process)
Sling swivelstud (Will be attached to free float tube)
|Enoughprep, let's begin shall we?Why it's necessaryto mention removing the magazine and making a visual check of the chamberto make sure the rifle is unloaded was beyond me. Until I saw someoneat the range standing in front of the muzzle and tinkering with it whileit was "cocked and locked". When the range officer accosted him about ithe said "Its okay, the safety is on..." Sounds like famous last words inmy opinion.|
So, far be itfrom me to break with a long established tradition and assume all humanlife on this planet is intelligent. Remove the magazine, lock the boltin the open position and visually check the chamber to ensure the rifleis clear.
Place the riflein a padded bench vise or cleaning cradle. If you purchased the recommendedlower receiver vise block, slip it into the magazine well and clamp itin your bench vise. Stand back about five feet so you can get a clear viewof the entire rifle. Now take a last look and make sure you want to dothis. It isn't all that difficult but changing a factory configurationalways makes me nervous.
|New HandguardInstallationIt's finally timeto install that new handguard. First, coat the threads of the new handguardand the receiver with a good lubricant. I used the same W.W.II issue weaponsgrease that I applied to the barrel earlier. If you don't lube the threadsthere's a good chance they will gall and you won't be able to properlytighten the handguard. The criticality of tightness will be come apparentshortly. The type of handguard you purchased may be a one, or two pieceunit. Either way, installation is pretty much the same except with a twopiece unit you'll install the base first, and then attach the tube.|
Your new handguardis probably coated with some protective finish such as Parkerizing. Thismaterial may be on the threads and may cause a tight fit or binding. Thisis another reason we lubed the threads. Carefully start the unit on thethreads, making sure it is not cross threaded, and begin turning it in.Slowly work the handguard back and forth on the threads while graduallyscrewing it in to help clear out the coating residue and sharp edges onthe threads. Gradually screw it all the way in until the unit stops, butdon't tighten it up just yet.
If you plannedto install a sling swivel or bipod mount on your free floated handguard,wait until the tube is installed and the proper "indexed" position is reached(See below).
Re-check to makesure you have the upper unit properly installed in the action block andit is locked down in the bench vise. DO NOT try to tighten the handguardwhile the lower unit is attached to the upper or without an action block,as you will seriously damage the action and/or lower unit.
|If you recall,we noted the location of the gas tube opening in the face of the receiver.Many free float hand guards have holes in the back of the unit surroundingthe threads. One of the holes in the back of the handguard must line upperfectly with the gas tube opening in the receiver when the unit is tightened.This is known as "indexing" the handguard. If you are fortunate, one ofthe holes will line up with the gas tube opening when the unit is tight.However, for those of us destined to be Murphy's chew toy, you will haveto really bear down on that handguard to get it tight as well as line upthe holes.If you have aone piece unit, this is where your strap wrench comes in. If you have atwo piece unit, you can use the Armorer's wrench to tighten the base andthen install the tube.|
Now comes anotherpotentially frustrating point in the project, removing the gas tube fromthe old gas block. However, there are several ways to minimize the frustration.Once this is done, you may install the sling swivel or bipod mount. Thefirst and by far the easiest is to re-use the old gas block with the gastube still installed. I know, it still has the post sight on it and gettingrid of that was one of the main reasons for doing this project in the firstplace.
|Torectify this little problem we are going to use recommended tool number9, the hacksaw. We are going to cut the tower off the gas block. Beforeyou get all upset, take a look at the unit I modified and the configurationinstalled by Bushmaster Firearms on an original factory 20 inch V-Matchrifle. Bushmaster does the same thing we are about to do, remove the sightpost from the gas block. If you are fortunate enough to own, or have accessto, a milling machine you may choose to use that instead. But I don't,so...Carefully clampthe tower in your bench vise. Clamp it on the end you will be discarding,the upper part of the post. DO NOT clamp it at the base where the gas blockfits over the barrel as it will probably deform the rings then you won'tbe able to get it back on the barrel. Cut the legs off the tower off thebase about 1/8th-inch of above the base itself. This will leave some metalto be ground off with a bench grinder, and then smoothed with a file.|
Be careful notto take too much metal off and grind into the base. Round off the edgesand use a fine file to give it a smooth finish. I touched up the shinyareas of metal with Birchwood Casey's "Alumablack" resulting in a finishthat nicely matched the Parkerizing.
If you are usingyour original gas block and not installing a new gas tube as we just discussedyou can skip the next section, "Gas Tub Installation" and proceed to "GasBlock Installation".
|Gas Tube InstallationIf you opted toreplace your gas block with a new one, such as a clamp-on or rail-typeas shown here, you will need to install the gas tube first. You can re-useyour old tube but I'd recommend a new one. The old one will likely havecarbon deposits on it that may cause it bind before it's seated properlyin the gas block. This could cause you to use levels of force or profanitythat may damage the tube, the gas block, your marriage, your relationshipwith your dog, neighbors, children and so on.|
The difficultpart about installing the gas tube in the block is seating the tube deepenough in the block to insert the retaining pin while simultaneously aligningthe tube's gas port with that of the port in the gas block. However, thesealignments are critical and must be done correctly or the bolt will notcycle properly. Recommended tool number six, the Gas Tube Wrench, shouldcome in quite handy at this point. However, I didn't have one and so Iused a system of "southern engineering" consisting of wooden blocks, aclamp, and a standard hammer that I'd rather not discuss. Do it right,use the proper tool! I'll refer you to the manufacturer's directions onproper usage of the tool.
|Youshould note that the gas tube on an AR-15 is not perfectly straight. Ithas slight bends in it to better conform to the barrel shape. Make surethe tube is properly oriented when you attempt to install it. Do not attemptto alter the shape of the tube.As I mentioned,Murphy has it in for me and I immediately ran into trouble getting thetube to seat deeply enough in the new block to align the ports. Despiteall my efforts, only a small edge of the gas tube port was visible in theport of the gas block. After much head scratching and some research onthe net, I came up with a solution.|
I decided to sinkthe shaft in the block slightly deeper. I used a drill bit of the samediameter or slightly smaller than the diameter of the gas tube. First Iplaced the drill bit in the shaft and marked the bit with a red markerslightly above the opening of the block. This gave me a stopping pointso I didn't over extend the shaft. Keeping the drill vertical and beingcareful not to wallow out the shaft, I slowly deepened the shaft up tothe mark on the bit.
After cleaningall the metal shavings out of the shaft, I tried fitting the tube again.It was still slightly shy of my goal so I repeated the process, increasingthe depth very slightly. This resulted in the ports lining up perfectlyand I proceeded to install the gas tube retaining pin.
|Gas Block InstallationI originally installeda new rail-type gas block on my rifle. In attempting to keep this rifleas light as possible, I decided I would not use the rail-type gas blockto mount anything useful, so I modified and re-installed the original gasblock as discussed earlier. If I had it to do over again I would stillchoose to use the original gas block. In my opinion it is much easier.|
Re-installationof the gas block on the barrel is yet another tedious and critical step.Proper alignment of the gas ports in the block and barrel must be perfect.The gas block must not be too far forward or back on the barrel, and mustnot be tilted left or right. Otherwise we get that bolt cycling problemagain due to improper gas flow.
There are variousmethods and tricks to aligning the gas ports. I will describe the methodI found easiest. If someone has an easier, more precise method, I'd behappy to add it to this article. I wish I had pictures of this part foryou but unfortunately I didn't think to take any.
Using a precisionstraight edge, draw a line lengthwise on the barrel extending a coupleof inches on either side of and intersecting the gas port. Next, pick upthe gas block/tube assembly and slide the straight-edge inside the openingfor the barrel. Align the straight-edge so it intersects the center ofthe gas port and is perfectly parallel from front to back of the block.A set of precision calipers should work nicely for this. Now mark the frontand back of the gas block so the marks can be seen when you slide the gasblock back on the barrel.
Using your calipersor straight edge, measure the distance from the gas port in the block tothe rear of the gas block (The rear is towards the receiver of the riflewhen the block is mounted on the barrel).
Measure this samedistance from the gas port on the barrel towards the receiver and placea mark perpendicular (across) the line you marked along the barrel earlier.
There you haveit. The intersection of the line will show you how far to slide the gasblock onto the barrel. The marks on the front and rear of the gas blockalign with the line lengthwise on the barrel, so the block isn't tiltedon the barrel.
|Slide the gasblock/tube assembly onto the barrel and guide the gas tube into the openingin the face of the receiver. Work the gas block back onto the bulge inthe barrel and line up your alignment marks.If you are installingthe old gas block with the taper pins, it's easy to see how far back toslide the gas block. When the taper pins are installed the block will self-align.The tricky part is left and right tilt. If the block is even slightly tiltedyou'll have a hard time getting the taper pins to go in. But once theyget started, the gas block will align itself properly so you won't haveto worry about it.|
If you are installingone of the clamp type gas blocks, you need to be very careful to keep yourvertical and horizontal lines aligned as you tighten the clamp screws.Go slowly and keep re-checking the alignment as you tighten the screws.I used a thread locking agent ("Loc-tite") on the threads. But, use itAFTER proper gas flow is verified by test firing. I went back and tookout one clamp screw, applied the Loc-tite, re-installed and tightened thescrew and then moved on to the next screw. This ensures the gas block isn'tinadvertently moved.
|Reassembly andTest Fit|
Hopefully thehard part is all behind us now. But, don't slap a magazine in it and govarmint blasting just yet. Carefully and slowly insert the bolt and charginghandle in the upper. DO NOT slam the bolt closed. Slide the bolt forwardslowly, making sure it slides properly over the gas tube. Push it gentlyforward until it locks into battery position.
The bolt shouldslide easily over the tube and seat all the way forward in the locked position.If it binds or does not close all the way, you have either mis-alignedor bent the tube or perhaps installed the wrong length tube. I don't envywhat you'll have to do next which is figure out what is wrong and correctit. Once it all lines up correctly, pin the upper back on the lower unitand install your choice of sighting devices.
The smart thingto do at this point is to take your rifle down to a certified gunsmithand have him check your work. After that's done, we'll head out to therange and test fire this baby.
|Trouble Shooting(No pun intendedÂ… Okay, maybe it was intendedÂ…)|
You should beaware that the changes you made to your rifle will likely affect it's performancewith different types of ammo. . That means your lovingly developed handloads or favorite factory ammo may no longer be the most accurate. Youhave just changed the gas block, tube alignment, barrel harmonics and pressurepoints. I was lucky and my groups actually improved with my hand load recipe.Darn, you'll just have to spend more time at the range with your new toy.Ain't that a bummer...Bolt fails tocycle properly
That's about allthe help I can give you. If you are still having problems recommend consultinga qualified AR-15 gunsmith.
Good Luck, GoodShooting.