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How to Install an AR‑15 Gas Tube (Step-by-Step Guide)

When it comes to building or upgrading your AR‑15, the gas system is a critical part of the equation—and the gas tube plays a central role in cycling your rifle. Whether you're assembling your first AR or swapping tubes for a custom-length barrel, installing the gas tube isn't hard—but there is a right way to do it.

Here's how to choose the correct gas tube and install it like a pro.

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🔧 What Does the AR‑15 Gas Tube Do?

The gas tube channels hot gas from the barrel’s gas port back into the bolt carrier group, forcing it rearward to cycle the action. Without it, your AR‑15 would be a fancy single-shot rifle.

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🧰 Tools You’ll Need

• Bench vise with upper receiver block or reaction rod
• Roll pin punch set (especially 1/8")
• Small hammer or gunsmith mallet
• AR‑15 gas tube roll pin
• Needle-nose pliers (optional)
• Loctite (optional—low strength)

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✅ Step 1: Choose the Right Gas Tube Length

Match the gas system length to your barrel:

• Carbine-Length (approx. 7”) — for 10.5”–16” barrels
• Mid-Length (approx. 9”) — for 14.5”–18” barrels
• Rifle-Length (approx. 12”) — for 18”–20”+ barrels
• Pistol-Length (approx. 4”) — for short-barreled builds

Check your barrel for the gas port location and manufacturer specs. If in doubt, measure from the barrel extension to the gas port hole and match that with the correct tube length.

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✅ Step 2: Prep Your Upper Receiver

Secure your upper in a vise using a reaction rod or upper receiver block. This prevents stress on the receiver and gives you control.

Remove your handguard (M-LOK, KeyMod, or quad rail) if it’s already installed. You need full access to the gas block area.

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✅ Step 3: Insert the Gas Tube Into the Gas Block

Slide the gas tube into the rear opening of the gas block. Make sure the gas port hole on the tube faces down toward the barrel. The roll pin hole in the tube should line up with the corresponding hole in the gas block.

Tip: Use needle-nose pliers to help hold the tube steady if needed.

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✅ Step 4: Install the Roll Pin

Once the holes are aligned, use a small hammer and a 1/8" roll pin punch to tap the roll pin into place. This secures the gas tube to the gas block.

Be careful not to bend or crush the gas tube while doing this. Light taps work best—don’t go caveman here.

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✅ Step 5: Align the Gas Block

Slide the gas block (now with gas tube attached) onto the barrel. Align the gas port in the block directly over the gas port in the barrel. This is critical for proper cycling.

Secure the gas block using the included set screws or taper pins, depending on your system.

Some builders apply a dab of low-strength thread locker on the set screws for extra security.

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✅ Step 6: Check for Alignment

Before reinstalling your handguard:

• Look through the upper receiver’s gas tube hole and confirm the gas tube is centered

• The gas tube should slide smoothly into the upper’s gas key slot

• No kinks, no contact with the barrel nut, and no off-center tension

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🔫 Step 7: Function Check

Once everything’s assembled:

1. Reinstall the handguard

2. Run the charging handle—feel for smooth resistance

3. Dry fire, then cycle again

4. (Optional) Perform a gas test at the range using dummy rounds or live ammo

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🔁 Troubleshooting Tips

• Short stroking? Might be a gas leak—check alignment and seal

• Bolt not locking back? Could be a weak gas signal or too much buffer weight

• Carbon leaking around gas block? Normal, unless it’s excessive

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🧠 Final Thoughts

Installing an AR‑15 gas tube is one of those tasks that seems intimidating—until you do it once. Then it becomes just another step in the build process. As long as you match the tube to your barrel and take your time with alignment, you’ll be in great shape.

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🔗 Recommended Products from Mounts Plus

• AR‑15 Gas Tubes (Carbine, Mid, Rifle)
• Low-Profile Gas Blocks
• Roll Pin Punch Set – Gunsmith Kit
• AR-15 Upper Receiver Vise Block

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🙋 FAQ

Q: Can I reuse my old gas tube?

A: Technically yes—but if it’s carbon-caked or bent, replace it. They're cheap insurance.

Q: Should I use Loctite on gas block screws?

A: Yes, blue Loctite (low strength) is recommended for set screws. Not needed for taper pins.

Q: What if the gas tube rubs on the barrel nut?

A: You need to realign your gas block or choose a different handguard/barrel nut combo.