Free Float The Barrel Of Your AR-15 Rifle
Tap Into the Full potential of AR-15 Accuracy by Free Floating the Barrel.
By Joe Gorman
Out of the box my Colt Sporter Competition AR-15 Flattop throws sub-inch five shot groups at 100-yards but depending upon where I placed my sandbag supports--close to the receiver or out near the front sight assembly--my groups would center over an inch apart.
For instance, if I zeroed my rifle with sandbags under the forearm, near the receiver, subsequent groups fired with the sandbags pushed forward near the front sight assembly would print over an inch higher in many cases. Similarly, if I used the sling it pulled groups to the side. The A2 barrel modifications went along way to minimize sling induced shot spreading but because the sling acts directly on the barrel, it is still present. This will not do.
I do not compete with my AR-15. My AR is primarily a prairie dog/varmint rifle. I want to pull my rifle out of the safe, after I've sighted it in at the range, go out in the field and throw groups exactly where my cross hairs line-up on any given day of the year. I don't want to try and recall where my sandbags were when I sighted in last time. Basically I want an idiot-proof, accurate rifle.
The Colt Sporter Competition comes pretty close to my ideal varmint rifle. I like being able to detach the carrying handle and mount a 12X Leupold on MWG extra-high rings. I can get a better stock weld and find I can shoot better this way as opposed to a traditional scoped AR-15 set up. The best part about the Competition model though is the 1/9 twist chrome lined barrel. The 1/7 twist rate of the other A2 Colt AR barrels makes them more finicky about bullet weight. Dedicated target shooters will scoff at chrome-lined barrels because they are not as consistent as stainless match barrels. The stock, Colt, chrome-lined barrel has printed several sub-.80 center-to center, five-shot groups at 100 yards using 69 grain hollow-point boat tail match Federals or Winchesters. That is just awesome considering this AR has an eight-pound trigger.
My Competition has exhibited the change in group position phenomenon resulting from different sandbag support position. It is, therefore, a prime candidate for free floating the barrel. A local gun smith has seen many examples of an AR's average groups getting cut in half after free floating the barrel. He mentioned, he has yet to see a Colt Competition that won't throw five shot groups at 100 yards, using the Winchester or Federal matches, that can't be covered with a quarter after free floating the barrel! I'd say, free float it.
To free float the barrel you need the correct tools. don't try to cut corners here and rig something for the job. Spend the change and get the tools. Otherwise you may needlessly ruin your high dollar AR. Simply put, to free float the barrel you will need the following: a 1/2 inch drive socket wrench, a barrel vise block , a receiver vise block, an AR-15 combination wrench, a drift punch set, a rubber mallet, small sledge, a standard vise, a free float tube, two screw drivers, rosin, a nylon strap oil filter wrench, three hands and a little patience. I know that seems like a lot of tools, but you probably already have the punches, the vise , the small sledge and the rubber mallet. For the specialty tools and the free float tube, you can call one place--Brownell's in Montezuma, Iowa (515) 623-5401. They even have very skilled and capable hands on board if you should have any questions.
Once you have acquired the requisite tools the rest is simple. First ensure the AR-15 is unloaded. Separate the upper and lower receivers. Remove the Zytel handguards and pull out the bolt carrier assembly. Insert the barrel into the barrel vise block and lock securely. With the AR-15 combination wrench remove the flash suppressor. Remove the barrel vice block from vice and remove barrel from the vice block. Lay the barreled receiver, safety side up, on top of your work bench (if your work surface is not wood, you will need a thick leather or plastic pad or some other protective surface). Drift the two, front-sight retaining-pins toward the ejection port side as they are tapered and can only be driven in that direction. Strike the front sight housing with the rubber mallet, driving it toward the muzzle end. The gas tube will come out with the front sight and can be left on if the factory barrel is to be reused.
With the front sight and gas tube off of the receiver, insert Zytel bolt substitute (included with receiver block) and clamp receiver vice block around receiver. (Note: if you have a Flattop, you may have to rout a channel out of the receiver vice block to get it to fit. They are designed for standard AR-15s. See photo) Lock receiver block insert into vise and loosen barrel nut with AR-15 tool. With barrel nut loose, the C-style retaining ring can be removed. Here is where that third hand comes in. You could use an assistant right about now. With two screwdrivers, spread the lips of the C-ring and have your assistant push it back toward the receiver to release it. Now the barrel, barrel nut, spring and retaining rings can be pulled away from the receiver. Reinstall the barrel into the receiver.
Apply a light coat of grease (I prefer to use the high-tech Tetra grease) to the new forearm assembly's shoulder, where it rests on the inside of the receiver. I used the excellent DPMS aluminum tube, also available from Brownell's. Its long flutes aid in control of the rifle and it comes with a sling swivel stud--secured with a nut on the interior of the tube--already installed. Thread the tube on the receiver hand tight and you should notice the sling swivel stud is not quite aligned. You will need to use the strap wrench to turn it till it is properly aligned. Spread rosin around the middle of the tube and wrap the nylon oil filter wrench's strap over the rosin. The rosin will help the nylon strap grip the tube. Turn the tube until the sling swivel is straight up-and-down, the gas tube hole near the receiver should then be aligned and you will be done. don't fret about the specified 30-45 foot pounds of torque the armorers' manuals call for when installing the barrel nut (or in this case the forearm tube). By the time the sling swivel, and the gas tub hole is in position, the torque is right.
Slide the front sight assembly, with gas tube, back on the barrel, being careful to guide the gas tube into the receiver hole. Push the taper pins back into the front sight as far as you can get them with your thumb and remove the barreled action from the vise. Support the front sight assembly on the bench surface you used to remove these pins and drive the front sight pins back home. Thread the flash suppressor and the stainless washer back on the barrel and put the barrel vise block around the barrel. Lock it in the vise and, using the AR-15 combination tool, tighten the flash suppressor until it is aligned (slots are even).
And there you go. You have just made your AR-15 a lot more consistent. Now you can support your rifle on any section of the forearm and your groups will stay in the same spot. providing of course you do your part.
Now, about that trigger...