DIY AR-15 Build: Front Sight Base Installation - ITS Tactical

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DIY AR-15 Build: Front Sight Base Installation

By The ITS Crew

4 of 8 in the series DIY AR-15 Build Upper

Continuing our DIY AR-15 Build, today we’ll be installing the Gas Tube and F-Marked Front Sight Base onto our Bravo Company 14.5″ Barrel and nearly completing our Upper Receiver.

Something to pay particular attention to at this point is that your gas tube properly fits through the port that’s left in the upper receiver after torquing your barrel nut down. We described this in our last article and it’s a pain to have to take a rail system apart when you find out the hole you thought was aligned, really wasn’t.

The tools and suggestions in this article will help you in the assembly of these components and hopefully save you from the mistakes that we’ve made in the past when working with the AR platform.

Let’s get into the next step in your AR-15 build!

F-Marked Front Sight Base

We highly recommend the F-Marked Front Sight Base from Bravo Company USA if you’re using a Mil-Spec Flat Top Upper Receiver, as it properly aligns the height of the FSB with the Mil-Spec Height of a Rear Iron Sight. The “F” simply means Flat top.

We’ve chosen to show the Front Sight Base install, rather than a Low-Profile Gas Block, as it’s fairly self explanatory to install and there are many different styles. A Low-Profile Gas Block takes the place of a FSB, allowing the Gas Tube to be installed and for the rail to ride “over” the gas block to give the rifle a slick look. A flip-up front sight like the Magpul MBUS will need to be used in conjunction with a Low-Profile Gas Block if a front sight is desired.

DIY AR-15 Build: Front Sight Base Installation

Taper Pins

If you’re starting from scratch with this build and are using a Barrel and Front Sight Base that aren’t cut for Taper Pins, you have the option of either using a Low-Profile Gas Block, or taking your barrel to a gunsmith to get these drilled. Please do not attempt this yourself unless you’re confident in what you’re doing. If the Taper Pin holes are mis-drilled/reamed in the barrel and FSB it can cause your FSB to shift and for the AR to lose its zero.

DIY AR-15 Build: Front Sight Base Installation

This is one of the main reasons we used a complete Upper Receiver Group from Bravo Company. Most everything is doable by yourself on this AR build with the exception of drilling/reaming the Taper Pin Holes and permanantely attaching/welding the Compensator if you’re using a 14.5″ Barrel as we are (described in the next article).

A 3/32 Taper Pin Starter Punch will not only make the installation of the Taper Pins easier, but will also help if you need to remove them as well. This can be done with standard punches as well, but the Taper Pin Starter Punch makes life easier. Another must is a Front Sight Bench Block, which  is conveniently marked with “Pins In” and “Pins Out” to avoid confusion on which side of the FSB to insert the tapered end from and which side to punch out.

Parts Needed

Tools Needed

Assembly Instructions

DIY AR-15 Build: Front Sight Base Installation

  • Ensure the bend in the Gas Tube is angled up to follow the contour of the barrel.
  • Insert the end of the gas tube that has the two holes into the Front Sight Base with the large hole facing down towards the gas port cut into the barrel.
  • Use the #2 roll pin punch to align the small hole in the gas tube (cut for the gas tube roll pin) with the front sight base.
  • Using the #2 roll pin holder, drive in the gas tube roll pin and finish with the #2 roll pin punch so that it’s flush with the FSB.
  • Take the complete FSB and slide it into the rail system, ensuring the gas tube is directed into the hole in the upper receiver.
  • Don’t manhandle this step, if the gas tube isn’t going in easily, there may be a problem with the barrel nut alignment.
  • Place the FSB into the Front Sight Bench Block with the “Pins In” side facing up.
  • The FSB may not fit into the bench block with your rail system, but it’s still important to have the block backing the Taper Pins you’ll drive in.
  • Align the FSB holes with the cuts in the barrel (the Taper Pin Starter Punch works well for this).
  • Drive the Taper Pins into the FSB, ensuring the smaller end or tapered side is inserted first.
  • Once installed, the Taper Pins will stick out slightly on the opposite side of the FSB.

Join us back here soon for our 5th installment in the DIY AR-15 Build (Upper Receiver) where we’ll be permanently attaching the BattleComp Compensator!

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  • Ken Stroede

    Great info, im realy glad you guys did this series. Ive been thinking about swapping out the FSB on my pre-assembled Del-Ton upper for a low pro gas block. I just havent done it because wasnt sure i could do it myself. Thanks for the class!!

  • kyle

    I was looking at not doing a set front sight as I like the magpul flip up sights what part would take the place of the front sight for my set up ?

  • Brian C.

    As you mention, Bravo Company sells the assembly which includes the upper, barrel, FSB, and gas tube. They can also add and pin the compensator of your choice to the barrel.

    Several questions: If you order without pinning/welding the compensator the site states NFA Rules Apply. If you have all of the parts and plan to assemble the gun and pin / weld the compensator, but have not done so, does this violate the “intent” portion of the NFA? Secondly, If i wanted to install a similar rail system, I would have to remove the barrel. If I order the compensator pinned to the barrel, is there enough wiggle room with the FSB to be able to remove the gas tube so the barrel can be removed?

    Thanks for the help in advance and thanks for the information in this series!!

  • Jack

    Don’t mean to nit pick here, but that is an example of the wrong way to use a torque wrench. If you find yourself in a situation, such as here, where you have to use another tool in conjunction with the torque wrench, then you should alighn the torque wrench up as to make a 90 degree angle with the tool being used. The reason for this is that adding another tool to it like that actually adds length to the workign fulcrom. You dial in say 15 ft lbs, but are actually applying more torque than that to the work at hand. Setting it up at a 90 degree angle adds no lenth to the working fulcrom. I’m an aircraft mechanic by trade and was taught this while earning my A&P license. We were taught this and had to demonstrate knowledge of this during a hands on evaluation by an FAA evaluator. Also, you only click the torque wrench once. Don’t click it twice just to “make sure”.

  • Guest

    @Brian C. I’m a newbie but familiar with BATFE rulings. I believe the excentricities with this “unfinished barrel would have to have those permanent issues complete before you complete a working rifle or complete upper.

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