How to remove/swap/install an AR-15 barrel/gas tube/delta ring
Alternate thread title: How I built a beater AR for around $400.
I was one of the debatably lucky ones who got in on the Khalan Weaponry "five AR lowers for the price of four" deal a while back. They took forever to come in and the quality was kind of spotty but in the end they were all basically functional so I'm still happy. I had one last rifle lower that I wanted to turn into a beater carbine for equipment/ammo trials and for training.
Cost of receiver: $75
I bought a 10.25" A2 heavy barrel pistol upper from a member of another forum to go on a pistol lower purchased through the above deal. The upper was complete except for no bolt, bolt carrier, or charging handle although it did come with some First Samco railed handguards which I promptly transplanted to another AR. Since I had no other uppers to work with for this project and I wanted to upgrade my pistol to a flat-top, I decided to commandeer this upper for the beater rifle build. If I remember correctly, I paid $275 for this upper.
Total cost so far: $350
Minus say $100 for the pistol barrel which will be used on another upper and minus say $30 for the railed handguards which went to another gun: $220
I shopped around for lower parts and found that one of the best deals without buying used or waiting forever for backorders was to get them through Sportsman's Guide using my secret member discount. I got a no-name 4-position collapsible stock assembly for $25, and I got a DPMS lower parts kit for $40.
Total cost so far: $285
I still needed the bolt stuff. I had a bolt carrier with a non-staked carrier key sitting around that I think I paid $50 for, and I ordered a brand new CMT bolt from Rainier Arms when it was on sale for $50. A charging handle was $15.
Total so far: $400
I still needed a barrel that was legal for use on a rifle. I looked around for a while but every barrel I could find was over $100, even used ones… Until I stumbled across a machine gun rental shop in Las Vegas that was selling off used M4 barrels from their rental guns. They said the barrels were heavily used and no longer accurate. I didn't care that much - I was mainly looking for function since most of the time this would just be used for shooting blanks. Cost of barrel: $25.
Grand total for parts: $425.
Okay, now that I've patted myself on the back for building an AR with mostly questionable parts, let's get to the meat of the article: how to swap barrels out on an AR-15.
First, gather your parts on a beige carpet.
Then, assemble the necessary tools. You will need an AR barrel wrench, a thin punch, a small hammer (or a big one I guess), a set of snap ring pliers, and some vise grips. If you've got an actual vise and a set of AR-15 action and barrel vise blocks, that's great. I don't have any, so I improvised. Not pictured: A socket wrench to increase leverage on the barrel wrench.
Remove the bolt assembly and charging handle. Then pull the handguards off. You can do it. If you have trouble, keep trying. You'll only learn by doing it yourself, Popeye.
If you look up front at the front sight assembly, you'll see that the gas tube originates from it and goes on back into the upper receiver. In the center of the photo, you can see a small roll pin that goes through the front of the gas tube and holds it in place. You'll want to take your punch and hammer and tap the pin out. Don't lose the pin or else you'll be on the phone crying to your favorite AR parts dealer.
Once the gas tube pin is out, grab a hold of the gas tube and twist/wiggle it back out of the front sight block. Depending on how dirty it is, it may take a lot of effort. You may need to apply cleaning solvents or penetrating lubricants. Only as a last resort should you grab onto the gas tube with the vise grips to help you pull it out. Be extremely gentle if you use any tools on the gas tube itself, or else you'll be on the phone crying again.
There are a couple of ways remove the gas tube. Notice the slight bend in the gas tube - the hole in the front sight base is lower than the hole in the receiver. You can rotate the gas tube 90 degrees so that the front of it clears the front handguard cap, and then pull the gas tube out to the front. It may be easier, however, to just push the gas tube out backwards through the receiver. Again, be very careful not to bend the gas tube.
While I still had the old barrel on the receiver, I figured I'd get the flash suppressor off. My barrel wrench has three different-sized openings at one end to accommodate different flash suppressors. If your barrel was factory-assembled, the flash suppressor may be attached very firmly, in which case you’ll either have to go the barrel-block-and-vise route or just take it to a shop and beg them not to charge you $50 to simply unscrew a stuck piece of metal. I lucked out and was able to get the flash suppressor off the pistol barrel with moderate wrenching.
Now you get to use the other end of the barrel wrench. There is a large slot in one end of the wrench and there are three pins sticking out around the perimeter of the slot. These pins engage the barrel nut as follows.
There is also a square hole in the middle of the barrel wrench that is used to add a socket wrench for more leverage. You will almost always need to do this.
Again, the barrel nut may be extremely tight depending on where it came from, who assembled it, and how dirty it is. Mine took a shitload of wrenching. I ended up getting a lever of equal length to the socket wrench I was using on the barrel wrench and hooking the second lever through the upper receiver (I guess the attached carry handle is good for something after all!). I knelt on one lever and pushed on the other. Nothing. Finally I grabbed a lever in each hand and pushed against the receiver in the middle with my foot. After some straining, grunting, and swearing, the barrel nut broke free. Unscrew the barrel nut all the way. The barrel itself should now come free from the front of the upper receiver, but again depending on how new or dirty it is it may take some effort.
Once the barrel is off, take a look at the rear of the barrel nut and delta ring assembly. You will see a snap ring on the back, holding the delta ring and delta ring spring in place. Notice also how the gap in the snap ring lines up with the gaps in the spring and the delta ring, and also lines up with one of the notches on the barrel nut. This is (duh) where the gas tube goes through into the receiver.
Next, take your snap ring pliers, spread apart the snap ring, and remove it. The delta ring spring and delta ring itself can now be removed. The barrel nut stays on the barrel unless you want to mess around with taking the front sight block off, which, at least with mil-spec units, can be another pain in the ass.
Reinstall the delta ring, spring, and snap ring on the new barrel. Install the barrel on your receiver. You can see that there is a post on the barrel extension that fits into a corresponding notch in the receiver.
Now use the barrel wrench to tighten the barrel nut. There are probably specific figures out there for torque and such, but I tighten it until two criteria are met: the barrel nut is tight, and one of the notches lines up with the gas tube hole in the receiver. After the barrel nut is tight, insert the tip of the snap-ring pliers or a similar implement into the gap in the snap ring and rotate it so the gap lines up with the gas tube hole in the receiver. Likewise, make sure the delta ring and spring are lined up. Now you can check the alignment and see if you need to do any more wrenching.
Fit your gas tube back in place. This is usually done by putting the back of the tube through the delta ring assembly and into the receiver (while holding the gas tube so that the bend is perpendicular to the floor if the receiver is sitting upright), then rotating the gas tube so that the lower front section lines up with the hole in the handguard cap and front sight base. You can also insert the gas tube from the back, so do whatever’s easiest. This is usually the point at which you realize that the barrel nut and delta ring assembly only LOOKED like they were lined up, and you need to do some fine-tuning with the barrel wrench. At any rate, do what you need to do without bending or denting the gas tube.
Fit the gas tube forward into the front sight base. You may need to clean the gas tube cavity in the front sight base out, depending again how dirty your barrel is. Make sure the gas tube pin hole is lined up. Find the gas tube pin that I told you a thousand times not to lose and gently tap it back into place. Note: there is a school of thought that says any time you remove a roll pin, you replace it with a new one. I generally believe in this theory, but in this case I was building a beater rifle whose purpose in life is to be tortured. If the pin breaks after a hundred rounds, well, then I order a new one and chalk it up to science.
Put the handguards back on. Insert the charging handle and bolt, checking for fit. An unusually tight fit toward the front part of the bolt’s travel may indicate that your gas tube is bent or misaligned. Go back and correct as necessary. Install the upper on the lower, and perform a parts check: make sure you don’t have any spare parts lying about (besides the barrel you just removed). Now perform a function check. Cycle the bolt a few times, making sure it seats fully when released. Lock the bolt open, then hit the bolt release. Dry fire. Cycle the bolt again. Put the safety on and pull the trigger (hopefully nothing happens). Put the weapon back on fire. Dry fire, but hold the trigger to the rear while cycling the action once more. Release the trigger and listen for the click of the hammer coming free from the disconnector. Pull the trigger again. If everything works to your satisfaction, give it a try with live ammo. If you have blanks and a blank adapter, you may want to try that first. That way you may even be able to get away with testing it in the comfort of your own home!
So anyway, here’s the final product. An A2 AR with an M4 barrel and a CAR stock. I’m mostly going to use it for training purposes either with blanks or empty for simple weapon handling drills, but I will take it to the range eventually to see just how shot out that $25 Las Vegas barrel is.
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Originally Posted by infrared35
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