Double feed
12AUG03

Defined as two live rounds trying to feed into the chamber at the same time. 99.9% of the time caused by a faulty magazine. The other .1% is overfunction resulting in the bolt striking the inside of the LRE hard enough to jar rounds from the magazine. Often seen on rifle with too large of a gas port and too weak of a buffer spring or too light of a buffer.

Short stroke
21JUL03
20JUL03
03AUG03
02NOV03
10.5 Upper question. #%*!&@ thing won't run!

The short stroke check is outlined in the Troubleshooting Checklist Part 1 Part 2. The gas tubes (the end that fits into the carrier key) and the gas rings are designed to wear out. They should be the first things you check if your rifle starts shortstroking assuming that your ammo is good. The next thing to look at is your bolt carrier key screws. Make sure they are tight using a wrench and make sure they are staked. Make sure the gas tube is properly installed (not upside down) and the gas tube roll pin is present. Staggering your bolt rings does nothing to improve the gas seal, having them aligned will not cause shortstrokes. ARs shouldn't malf due to lack of cleaning with less than 1,000 rounds through them. If your rifle only works "when clean,” the real problem is that it doesn't work "when hot.”

FSB removal
FSB removal - just call me the master!
Swapping out front sight bases? In over my head!

These instructions cover the first removal of an FSB. The first removal is usually the most difficult. All directions given (left, right, top, and bottom) are from the perspective of the firer with the rifle held normally. If you wish to remove the FSB completely, you will also have to remove any muzzle device installed on the barrel. A sturdy work surface is necessary for this procedure. If you lack a proper bench then work on an adequately covered concrete surface.

Pinned on FSBs are NOT interchangeable by the average user. Taper pin location and depth varies with each barrel.  This is normal; the prime end user of the M series considers the barrel to be an “assembly”. For their purposes, the FSB is a permanent part of the barrel.

To remove the front sight base from your AR barrel you’ll need the proper tools.

A medium size (8 oz or so) hammer. For me, a ball peen hammer works best.

1/8” drift, or pin, punch to remove the taper pins. Mine is a Craftsman.

A 1/16” pin punch to remove the gas tube roll pin. I have never used my set of roll pin punches. My small punches are mostly Starett’s.

A much larger punch, in the area of ¼” in diameter to start the taper pins. Mine is home made from a length of tool steel.

An armorer’s block, preferably plastic, to support the barrel. Mine is home made with some custom drilled holes to allow for the taper pins in their extended position. The block must be tall enough to keep the hand guard cap from touching your work surface but not so high as to cause difficulty in striking the taper pins.

Some grease. Thicker is better. I use RIG. It’s in the shop.

Some folks let the FSB sit overnight in penetrating oil. While I have never had to do this, it cannot hurt if you have the time. Kroil seems to be a favorite.

Taper pins are exactly that, tapered. One end is smaller. They only come out from one direction. The small end, the end you must hammer on to remove them, is usually on the left side of the FSB. Properly installed taper pins should protrude equally from both sides of the FSB or the large end should be flush with right side of the FSB. Remember where your taper pins sit in relation to the FSB. You will reinstall them to the same depth.

Remove the hand guards and the gas tube. The hand guards will cause the upper to rock and force the rear of the upper to sit too high. Either situation will make firm hits on the taper pins difficult. Later, you will have to rotate the FSB on the barrel and the gas tube will prevent this.

Apply grease to the barrel forward of the hand guard cap. Apply it liberally; it will prevent scratches in the finish of the barrel that may occur during removal of the FSB.

Set the barrel on the armorer’s block. Ensure that the hand guard cap is not touching your work surface (bench) and that the barrel does not rock or rotate when seated. Sometimes it is easier to remove the sling swivel than to fight with it touching your bench.

Place the large starter punch squarely over the small head of the taper pin and strike the starter punch as if you are trying to drive a large nail into a block of wood. Hold the punch firm and vertical. Do not allow the punch to slip. Per the warning on my hammer, safety glasses are a good idea. Some people mask the area of the FSB around the pins with tape or cardboard to prevent any scratches from an errant punch. If you have the time, it cannot hurt.

Check the head of the pin to make sure it is not mushrooming. Taper pins are supposed to be hardened. They should not deform in normal use. If they do deform they are probably soft and you will want to stop here. You can check the hardness of the pins by lightly passing a file over them. If the file grabs, or “bites”, the pins are soft.

If you did everything right, the head of the pin should seat flush with the surface of the FSB with one or two strikes. If this does not happen, make sure your set up is solid and try again. Keep an eye out for any deformation on the head of the pin. A small white dot in the surface finish there is normal. Once the heads of the pins are flush with the surface of the FSB, continue to the next step.

Carefully align the 1/8” punch on the head of the pin and drive out the pin. Again, hold the punch firmly and vertically and tap the pins out of the FSB. Do not drive them as you did with the starter punch.

With the pins removed, spin the FSB on the barrel. Do this several times to break off any burrs and release any blasting media, or Parkerizing salt, left there during manufacture.

Gently pull the FSB from its seat. This is the part most people rush so go slow. Be careful that the front edge of the FSB does not drag on the top of the barrel during removal. Contact between the FSB and barrel will cause intermittent semi-circular scuffs in the finish of the barrel. If you see a barrel with these scuffs, you can be certain that the assembler was a clod. Remove the FSB as far as necessary to affect the required repair or modification.

Remove the hand guard cap if necessary. If removal is not necessary then secure the hand guard cap. The hand guard cap can rattle around and scar the finish or become damaged.

Things to check after removing the FSB:

Size of the gas port. Most gas ports are very small. Using a caliper to check the diameter is often not feasible. If you lack pin gages a set of appropriately sized drill bits will suffice. With the proper drill bit installed in the gas port sight through the bore and ensure that the gage is centered and vertical.

Location of gas port. The center of the gas port should be 0.295” +/- 0.005” from the shoulder of the barrel on which the hand guard cap seats. Some companies do measure from the front face of the barrel extension to the center of the gas port so there is often a variance in the 0.295” dimension. The 0.295” dimension relates mostly to the fit of the hand guard cap to the barrel. More important than the 0.295” dimension is the location of the FSB relative to the gas port. A quick check of the gas port location is the ring of Parkerizing around the gas port. During Parkerizing, the corresponding port in the underside of the FSB creates this ring. Several manufacturers finish their barrels after assembly. This leaves the areas under the FSB unfinished. On properly finished barrels one can often seen a ring of carbon, instead of Parkerizing, around the gas port.

Depth of taper pin cuts. The “tunnels” for the taper pins should not be deeper than one-half the diameter of the pins. Damage to the bore could result if the cuts are deeper. Taper pins installed too deep into the barrels are often very difficult to remove.

Internal geometry of FSB. If you remove the FSB from the barrel, there is a chance to the check the “guts” of the FSB. To check them properly you will have to remove the sling swivel. With the swivel removed, you will be able to see a hole in the FSB between the “legs” of the swivel mount. This hole ties to the gas tube bracket of the FSB. Ensure that all holes are free of burrs and debris. Install the gas tube and secure it in place with a 1/16” punch though the gas tube roll pin hole. Ensure that the gas port in the FSB lines up with the gas port hole in the gas tube. As a check, you can insert a drill bit of the proper size through the FSB and into the gas tube. You should be able to spin the drill bit by hand if the holes line up.

Rust on the hand guard cap. Improperly finished barrels often have rust on the front and rear of the hand guard cap around the larger hole. On the front, the rust usually follows the shape of the FSB. The rust is less obvious on the rear and usually follows the shape of barrel shoulder. Check for rust on the FSB too. Clean and repair as appropriate.

Tips for reinstalling the FSB:

Clean the inside of the FSB. Remove any rust, burrs, or fouling.

Grease the inside of the FSB. Check that the grease on the barrel is intact.

Clean the FSB seat. Remove any rust, burrs, or fouling. Grease never hurt.

Install the hand guard cap first. It too can scuff the barrel so be careful. Make sure the hand guard cap is in its proper (gas tube hole up, flat surface forward) orientation. On some barrels, you cannot rotate the hand guard cap with the FSB installed.

Install the FSB carefully. Don’t rush the job or you will scar the finish. Make sure to keep the sling swivel from tangling with the hand guard cap. It sometimes helps to twist the FSB onto to the last few millimeters of its seat.

Wiggle the pins into place. Once the FSB is fully seated sight through the taper pin holes and make sure that, they align with the grooves in the barrel. Start a taper pin by hand and wiggle it with your thumb while minutely changing the orientation (along the barrel and around the barrel) of the FSB. The taper pin should seat nearly half its length. Repeat with the other pin.

Put them in as you took them out. Use the armorer’s block and starter punch again. Drive the pins into their original orientation but don’t get too crazy; tight is tight.

A little cold blue never hurt. Remember that white spot on the head of the taper pins? Cold blue or a paint pen work wonders.

Flash Suppressors
Flash hider messed up!help
Flash hider/flash suppressor torque: How much?
How do I take this off?
Three Prong flash hiders
Crush or peel washer?
Crush Washer, Which side is toward the front?

Vortex History and Questions
Original Vortex flash hider
Vortex FH: Mushrooming

to prevent