It is well known among precision shooters that any inconsistent external pressure on the barrel of a rifle will affect accuracy. The AR-15/M-16 is no exception. The standard A2-A3 configuration has a plastic handguard clamped to the barrel as well as a sling swivel. Attaching a sling or bipod to the barrel or handguard will have a detrimental effect on bullet impact, especially at long range.
This article will describe the process of free floating the barrel of the AR-15. It is written so a novice can understand the content. So if it sounds too simple or "over explained", gimme' a break. There are some of us that need a little more guidance.
DISCLAIMER: I am not a certified gunsmith nor even an expert. This article is intended to illustrate what I encountered during the conversion of my rifle. You should consult with, and have your rifle checked by, a qualified gunsmith before beginning any work on your rifle or attempting to fire it .
|The subject rifle
is a Rock River 16 inch flattop upper with standard front post sight and
a mid length handguard. Your configuration may vary, but the parts
and tools required are pretty much the same. Just be sure to verify what
length your handguard is when you order parts for your rifle. Although
not as common as the carbine and full-length handguards, the mid length
handguard configuration is becoming more popular.
If you bought a non floated barrel upper with the intention of doing this project to save yourself some money, stop here. By the time you purchase the necessary parts and tools to complete this project, It would have been cheaper to purchase an upper already configured to your specifications. However if, like me, you purchased one configuration and later decided you wanted something a little different, then by all means, proceed.
|Now before you
tear apart your perfectly good rifle, you might want to read this entire
article, including the troubleshooting section to see what you are getting
yourself into. They don't call it "troubleshooting" for nothing.
Of the major AR-15 parts and accessory distributors, I've found that Brownells is probably the best source. Therefore, I've already looked up and added the item number for some of the tools and parts you'll need. Below is a list of tools and parts for this project. Some are "required" and some are "recommended". I managed to get by with just the required tools. I included a hacksaw, but that was due to the configuration of my rifle and the configuration I wanted to end up with. Take a hard look at your project before you decide which tools you'll need.
One decision you need to make before you get started is whether you will be installing a new gas block, like one of the rail types described in this article, or the original gas block. The reason for this is the original gas block on this rifle configuration has a sight post on it. This will be removed from the gas block. (See details below.)
Tools - Required
Armorers Wrench - Brownells item # 231-000-007
Tools - Recommended
or plastic hammer
Parts - Required
Handguard of your choice, one or two piece
Parts - Recommended
Front sight taper
pins - two (Can use old pins if not damaged during removal)
prep, let's begin shall we?
Why it's necessary to mention removing the magazine and making a visual check of the chamber to make sure the rifle is unloaded was beyond me. Until I saw someone at the range standing in front of the muzzle and tinkering with it while it was "cocked and locked". When the range officer accosted him about it he said "Its okay, the safety is on..." Sounds like famous last words in my opinion.
So, far be it from me to break with a long established tradition and assume all human life on this planet is intelligent. Remove the magazine, lock the bolt in the open position and visually check the chamber to ensure the rifle is clear.
Place the rifle in a padded bench vise or cleaning cradle. If you purchased the recommended lower receiver vise block, slip it into the magazine well and clamp it in your bench vise. Stand back about five feet so you can get a clear view of the entire rifle. Now take a last look and make sure you want to do this. It isn't all that difficult but changing a factory configuration always makes me nervous.
the Upper Unit
Remove all non permanent items such as optics, mounts, rails, sights, accessories, as well as the bolt and charging handle from the upper unit. Otherwise, the upper will not fit in the action vise or damage may occur to these items due to the rough handling necessary in the next few steps. You can remove the "polymer" handguards but I left them in place until I removed the taper pins just in case I missed with my hammer and hit the barrel or gas tube.
Apply a good penetrating
oil or solvent to taper pins in the base of the front post (which is also
the gas block in case you didn't know). While you're at it, apply some
solvent to the junction of the gas block and gas tube, and the base of
the gas block and barrel to help loosen any carbon deposits that may hamper
its removal. Let the solvent soak in per manufacturers directions.
|Drive Out the
You can perform the next step in this procedure with the lower unit removed or still attached as I did. I felt it was easier to stabilize and support the entire rifle instead of just the upper unit.
It is imperative the rifle is supported in a manner that ensures there will be no stress caused between the upper and lower units when driving out the taper pins.
As you can see in the picture I used my garage floor but any flat, hard surface that won't flex or move will do fine. Lay the rifle (or upper) on its right side with the barrel and gas block supported by spacing blocks.
I used a section of 2X6 and placed a 1/8 inch hard plastic shim between the wooden block and the gas block. The plastic keeps the soft wooden block from compressing and absorbing your hammer blows and yet protects the gas block from damage. The barrel and rifle should be supported equally along it's length to ensure the barrel can not flex in the receiver while you are pounding on the taper pins with your whacking great hammer. You'll have to figure out the best way to do this depending on the configuration of your rifle. At this point I insist you don a pair of leather work gloves and safety goggles.
Removing the Taper Pins from the front post pins can be the most difficult and frustrating part of this conversion, closely followed by gas tube removal and replacement. If you "booger up" the pins, you'll have to drill them out or have them pressed out, neither of which is any fun at all. The pins, as the name implies are tapered. They can ONLY be removed by driving them out of the gas block from the LEFT to RIGHT.
TAke a close look at the ends of the taper pins. As you can see, the ends are rounded rather than flat as you might expect with most drift pins.
Use the Taper Pin Starter punch from Brownells to drive out the pins. This punch is specifically designed with a cupped tip to fit over the rounded ends of the taper pins, thereby minimizing the chance of mushrooming the taper pins and ruining your whole day.
Place the punch squarely over the pin and hold it perfectly vertical. Using the heavy hammer, strike the punch squarely and firmly to start the pin to moving. Don't beat repeatedly on the pin. Just give it one good smack and then assess the results. Once the pin begins to move, reduce the force of your hammer strikes. When the pins have been removed, examine them for damage. It's probably best to discard them and use new ones but... that's up to you.
Gas Block/Front Sight Post
It's finally time to install that new handguard. First, coat the threads of the new handguard and the receiver with a good lubricant. I used the same W.W.II issue weapons grease that I applied to the barrel earlier. If you don't lube the threads there's a good chance they will gall and you won't be able to properly tighten the handguard. The criticality of tightness will be come apparent shortly. The type of handguard you purchased may be a one, or two piece unit. Either way, installation is pretty much the same except with a two piece unit you'll install the base first, and then attach the tube.
Your new handguard is probably coated with some protective finish such as Parkerizing. This material may be on the threads and may cause a tight fit or binding. This is another reason we lubed the threads. Carefully start the unit on the threads, making sure it is not cross threaded, and begin turning it in. Slowly work the handguard back and forth on the threads while gradually screwing it in to help clear out the coating residue and sharp edges on the threads. Gradually screw it all the way in until the unit stops, but don't tighten it up just yet.
If you planned to 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 make sure you have the upper unit properly installed in the action block and it is locked down in the bench vise. DO NOT try to tighten the handguard while 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 surrounding
the threads. One of the holes in the back of the handguard must line up
perfectly 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 of
the 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 have
to really bear down on that handguard to get it tight as well as line up
If you have a one piece unit, this is where your strap wrench comes in. If you have a two piece unit, you can use the Armorer's wrench to tighten the base and then install the tube.
Now comes another potentially frustrating point in the project, removing the gas tube from the 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. The first and by far the easiest is to re-use the old gas block with the gas tube still installed. I know, it still has the post sight on it and getting rid of that was one of the main reasons for doing this project in the first place.
rectify this little problem we are going to use recommended tool number
9, the hacksaw. We are going to cut the tower off the gas block. Before
you get all upset, take a look at the unit I modified and the configuration
installed by Bushmaster Firearms on an original factory 20 inch V-Match
rifle. Bushmaster does the same thing we are about to do, remove the sight
post from the gas block. If you are fortunate enough to own, or have access
to, a milling machine you may choose to use that instead. But I don't,
Carefully clamp the 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 block fits over the barrel as it will probably deform the rings then you won't be able to get it back on the barrel. Cut the legs off the tower off the base about 1/8th-inch of above the base itself. This will leave some metal to be ground off with a bench grinder, and then smoothed with a file.
Be careful not to take too much metal off and grind into the base. Round off the edges and use a fine file to give it a smooth finish. I touched up the shiny areas of metal with Birchwood Casey's "Alumablack" resulting in a finish that nicely matched the Parkerizing.
If you are using your original gas block and not installing a new gas tube as we just discussed you can skip the next section, "Gas Tub Installation" and proceed to "Gas Block Installation".
|Gas Tube Installation
If you opted to replace your gas block with a new one, such as a clamp-on or rail-type as shown here, you will need to install the gas tube first. You can re-use your old tube but I'd recommend a new one. The old one will likely have carbon deposits on it that may cause it bind before it's seated properly in the gas block. This could cause you to use levels of force or profanity that may damage the tube, the gas block, your marriage, your relationship with your dog, neighbors, children and so on.
The difficult part about installing the gas tube in the block is seating the tube deep enough in the block to insert the retaining pin while simultaneously aligning the tube's gas port with that of the port in the gas block. However, these alignments are critical and must be done correctly or the bolt will not cycle properly. Recommended tool number six, the Gas Tube Wrench, should come in quite handy at this point. However, I didn't have one and so I used a system of "southern engineering" consisting of wooden blocks, a clamp, 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 on proper usage of the tool.
should note that the gas tube on an AR-15 is not perfectly straight. It
has slight bends in it to better conform to the barrel shape. Make sure
the tube is properly oriented when you attempt to install it. Do not attempt
to alter the shape of the tube.
As I mentioned, Murphy has it in for me and I immediately ran into trouble getting the tube to seat deeply enough in the new block to align the ports. Despite all my efforts, only a small edge of the gas tube port was visible in the port of the gas block. After much head scratching and some research on the net, I came up with a solution.
I decided to sink the shaft in the block slightly deeper. I used a drill bit of the same diameter or slightly smaller than the diameter of the gas tube. First I placed the drill bit in the shaft and marked the bit with a red marker slightly above the opening of the block. This gave me a stopping point so I didn't over extend the shaft. Keeping the drill vertical and being careful not to wallow out the shaft, I slowly deepened the shaft up to the mark on the bit.
After cleaning all 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, increasing the depth very slightly. This resulted in the ports lining up perfectly and I proceeded to install the gas tube retaining pin.
|Gas Block Installation
I originally installed a new rail-type gas block on my rifle. In attempting to keep this rifle as light as possible, I decided I would not use the rail-type gas block to mount anything useful, so I modified and re-installed the original gas block as discussed earlier. If I had it to do over again I would still choose to use the original gas block. In my opinion it is much easier.
Re-installation of 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 must not be tilted left or right. Otherwise we get that bolt cycling problem again due to improper gas flow.
There are various methods and tricks to aligning the gas ports. I will describe the method I found easiest. If someone has an easier, more precise method, I'd be happy to add it to this article. I wish I had pictures of this part for you but unfortunately I didn't think to take any.
Using a precision straight edge, draw a line lengthwise on the barrel extending a couple of inches on either side of and intersecting the gas port. Next, pick up the gas block/tube assembly and slide the straight-edge inside the opening for the barrel. Align the straight-edge so it intersects the center of the 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 front and back of the gas block so the marks can be seen when you slide the gas block back on the barrel.
Using your calipers or straight edge, measure the distance from the gas port in the block to the rear of the gas block (The rear is towards the receiver of the rifle when the block is mounted on the barrel).
Measure this same distance from the gas port on the barrel towards the receiver and place a mark perpendicular (across) the line you marked along the barrel earlier.
There you have it. The intersection of the line will show you how far to slide the gas block onto the barrel. The marks on the front and rear of the gas block align with the line lengthwise on the barrel, so the block isn't tilted on the barrel.
|Slide the gas
block/tube assembly onto the barrel and guide the gas tube into the opening
in the face of the receiver. Work the gas block back onto the bulge in
the barrel and line up your alignment marks.
If you are installing the old gas block with the taper pins, it's easy to see how far back to slide 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 tilted you'll have a hard time getting the taper pins to go in. But once they get started, the gas block will align itself properly so you won't have to worry about it.
If you are installing one of the clamp type gas blocks, you need to be very careful to keep your vertical 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 it AFTER proper gas flow is verified by test firing. I went back and took out one clamp screw, applied the Loc-tite, re-installed and tightened the screw and then moved on to the next screw. This ensures the gas block isn't inadvertently moved.
Hopefully the hard part is all behind us now. But, don't slap a magazine in it and go varmint blasting just yet. Carefully and slowly insert the bolt and charging handle in the upper. DO NOT slam the bolt closed. Slide the bolt forward slowly, making sure it slides properly over the gas tube. Push it gently forward until it locks into battery position.
The bolt should slide 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-aligned or bent the tube or perhaps installed the wrong length tube. I don't envy what you'll have to do next which is figure out what is wrong and correct it. Once it all lines up correctly, pin the upper back on the lower unit and install your choice of sighting devices.
The smart thing to do at this point is to take your rifle down to a certified gunsmith and have him check your work. After that's done, we'll head out to the range and test fire this baby.
(No pun intended… Okay, maybe it was intended…)
You should be aware that the changes you made to your rifle will likely affect it's performance with different types of ammo. . That means your lovingly developed hand loads or favorite factory ammo may no longer be the most accurate. You have just changed the gas block, tube alignment, barrel harmonics and pressure points. 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 to
That's about all the help I can give you. If you are still having problems recommend consulting a qualified AR-15 gunsmith.
Good Luck, Good Shooting.