Thursday, March 27, 2014

A2 Front Sight Modification to a Low Profile Gas Block

As previously posted, I recently purchased and received a PSA 14.7" CHF CL mid-length upper with a pinned flash hider. The next step on this project was to install a Fortis 12" REV rail and that meant removing the handguard, the handguard cap, the A2 front sight, the delta ring, weld spring, and snap ring. However, I wanted to retain the gas block on the A2 Front sight, therefore, it would have to be cut down and heavily modified to create a low profile gas block. Furthermore, because the flash hider is pinned, I decided to do the project with the front sight still attached to the barrel.

Before you get started, remove your upper from the lower (if attached), drop the guts (BCG & charging handle) out, and place them outside your workspace. 

Compile all the tools you will need for this project. I used whatever I had available, which probably made the process twice as long, however, I also did this project over the course of 3-4 days, in between my fulltime job and taking care of our one year old. With the right tools you could probably git 'er done without issue in a full day's work or less, all depends on your motivation & schedule.

My tool list:

         - Dremel 1 1/2" cutting wheel
         - Dremel bits from a sanding/grinding kit 
         - 1/16" pin punch 
         - Gas tube roll pin (to replaced the removed roll pin)
         - Hacksaw
         - Mill file
         - Pliers
         - Needle nose pliers
         - Birchwood Casey Super Blue
         - Aervoe Matte Black spray paint
         - Krud Kutter / Brake Cleaner
         - Painter's tape 
         - Eye protection
         - Dust mask
         - Vacuum cleaner with an extension wand or a portable handheld vacuum 

Wish I had:

         - An angle grinder (per this excellent video)
         - Tin snips

Let's get started.

[1] Remove the handguard

Before I attempted to remove the handguard I placed a block of wood under the upper receiver (pictured below) so that I would not place any pressure on the forward assist and to give me a relatively solid platform to work from.

I did not use any specialized tools to accomplish this action, I simply grasped the delta ring firmly (gloves might help), pulled down on it with my right hand, then used my left hand to hold onto the handguard while pushing the lower handguard off with my thumb and fingertips. Once the bottom of the lower handguard popped out, it was easily rotated out of the handguard cap (located behind the A2 front sight) and removed. Repeat the process to remove the upper handguard.

[2] Remove the gas tube

With the handguard removed, I marked my gas tube on both ends with a Sharpie marker to indicate where I should mask it off with painter's tape for the paint job to be applied later on.  I then used a 1/16" pin punch to knock out the gas tube roll pin. The gas tube was then removed and set aside.

With the gas tube now removed, I masked off the gas block on the front sight and the flash hider to eliminate unnecessary dust & debris entering the barrel. In a lot of the following images you'll see painter's tape moving to different locations, basically anywhere I'm working to mitigate nicks and scratches to the barrel, etc.....

Though not ideal, I have reused gas tube roll pins in the past without issue, however, for this upper I already had some unused roll pins on hand and tossed the roll pin I had just removed into the trash. Plan ahead for your modification and purchase some roll pins or reuse your roll pin. Your decision.

[3] Remove the handguard cap

This was an absolute PITA to do and tin snips, which I did not have, would have helped a lot. I resorted to cutting diagonally into the cap with my Dremel (as indicated above), getting as close to the barrel as possible without marring it, then using wire cutters (ineffective) and pliers to pry that mother off.

I also removed the sling swivel at this stage with the Dremel by grinding off the rivet end.

[4] Modify A2 front sight

To begin the modification I took off the major components of the A2 front sight (sling swivel, sling swivel tabs, bayonet lug, and the front post) by using my Demel tool and a hacksaw. An angle grinder would be have been the tool of choice in this stage, so if you have one, use it!

Throughout this stage there was a lot of residue and debris, this is where a handy portable vacuum comes into play. Additionally, you should have a dust mask and eye pro on. Be smart, not blind or suffering from some respiratory disease.

Throughout the deconstruction of the front post I also employed the use of a mill file to refine and grind down edges.

To get the hacksaw started on the correct path, I used the Dremel to cut in some guides.

With the major components now removed and the A2 front sight stripped down, I utilized the mill file to roughly grind down the edges and assessed the amount of additional material that needed to be removed in order to correctly fit the Fortis rail over the barrel.

The bottom of the gas block looks good, the top is going to need a lot of work.

Again, used the Dremel to cut guides and took off large chunks with the hacksaw. In between that, I used the mill file.

I finally reached a point where it looked decent and the fit was within tolerance, not a work of art, but functional. Edges were refined with the Dremel tool sanding bits.

With the major work completed on the gas block, I applied the Birchwood Casey Super Blue with a Q-Tip and then wiped away the excess with a damp towel. For those of you who do not plan to paint the completed gas block after the Birchwood Casey application, it does not have a black finish, more like a parkerized gray (as pictured below).

[5] Remove the Delta Ring +

Again, I employed the use of both the Dremel and hacksaw for the removal of the delta ring. I also wrapped the upper receiver with an old towel and taped it down to protect it before I got started on this section.

For the first cut I located the hole for the gas tube and rotated the delta ring from the top of the receiver to the side for a clear work space. Additionally, I also lined up the cut with a drop/indent on the barrel nut. The first cut was made with the Dremel for a guide and then straight to the hacksaw. The delta ring is a lot easier to cut than the front sight and it doesn't take much to power through it.

The delta ring requires two cuts on opposite sides and then it falls off.

To remove the weld spring and snap ring I used needle nose pliers. With a solid hold on the pliers, firmly grabbed an end point with the needle nose pliers, and rotated them off with force. Once you start, don't stop.

Slight marring on the barrel nut, but nothing significant.

At this point you may want to double check that the barrel nut is torqued correctly. If you have an AR combo armorer's wrench, Tapco makes a good one, make sure you create a 90º angle with the AR combo wrench and the torque wrench to get an accurate reading. If you loosen the barrel nut, do not use your torque wrench, only use a torque wrench to tighten the barrel nut into place. The barrel nut should be torqued into place no less than 30 ft-lbs to no more than 80 ft-lbs (30-80 ft-lbs).

[6] Paint & Reassemble

The next step before reassembly on my project was to paint everything with Aervoe Matte Black spray paint. This is purely for aesthetics. I degreased the areas I wanted to hit with Krud Kutter (available at big box home improvement stores or you could use Brake Cleaner ), then boiling water, dried everything off, and then masked with painter's tape. When the weather was decent, I took everything outside and applied two coats of Aervoe Matte Black to the parts.

I painted the gas tube separate from the upper, however, you can also reinstall the gas tube prior to painting and do it all at the same time. Either way works.

The gas tube was then reinstalled with a new roll pin.

After everything was fully dried, I gave it ~48 hrs, I then wrapped the barrel in a plastic bag to avoid any unnecessary marring, especially after a nice paint job, and sent it up through the rail.

The Fortis rail is relatively easy to install. I plan on doing a small post on how to do it correctly in the next couple of days, because I did have some initial issues with it and will cover that in the post. However, I'll just state that I tightened it into place (after removing the plastic bag) with a torque wrench for now.

Looking good.

Below is the set up after two range trips and prior to adding Magpul MBUS Pro sights. This is the same lower from my staking post, but I switched out the ACS stock for a slim MOE carbine stock. I also really like the slim profile of the Fortis rail, however, as stated previously, I did have some problems when I initially installed it. No malfunctions and no issues so far.

Final notes. Of course having the right tools makes a world of difference, but I still got 'er done and it turned out well IMO. There are gunsmiths out there that do an excellent job converting A2 front sights in to low profile gas blocks at a very reasonable price. If you don't have the resources or time to do it yourself, google them up, check their references, and send it out. 

Time for a beer, this post took forever.


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  2. Great job but why destroy a nice barrel with front sight(I found it hard to find for a nice price)instead of just buying a new one?Great step by step instructional though!

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