Updated: Dec 17, 2021
Once the rear sight block has been pressed and pinned, I install the front handguard latch. It’s a bit too tight, so I carefully filed out the notch so the lever can be moved by hand with a snug fit. Throughout the installation of the barrel I used this as a reference point. To ensure the barrel was put into the receiver straight, I clamped it into the soft jaws of my bench vice. Using a bubble level first on the receiver, then the handguard lock, I made sure everything was level and made some reference marks before pressing the barrel in place.
Now it’s time to address the gas block. I’m going to use the gas tube to determine where on the barrel this will be placed. Earlier I had mentioned that I had disassembled the spindle for the gas cut off from the block. This way I can drill out the gas port itself using the gas block as a guide, once it’s cross drilled and pinned in place.
At this point, this pile of parts is beginning to resemble an actual firearm.
I‘ve paused at this point to do yet another mock up by putting on the dust cover, the upper and lower handguards, and fitting the rear of the gas tube to the front of the rear sight block, where the gas tube latch is located. I checked for alignment of the gas block to make sure it’s not canted to the left or the right. I put the bolt and bolt carrier into the receiver to see how smoothly it reciprocated inside the receiver, and make sure nothing is dragging against it. Right now is the time to do any tweaking necessary to prevent the piston or any part of the carrier against the rear sight block or inside of the gas tub. I don’t want anything touching that shouldn’t be, and causing the mechanism to slow down.
I kept the old stub portion of the barrel where I got the gas block from during the demilling process. This will give me an idea of how large the gas port should be. Looks like a funny oval shape, doesn’t it ?
Well, holding the barrel at an angle, you can see it’s nothing but a round hole ai can drill out. Like I said, using the gas block as a guide, I can drill the hole on a bias. It’s what makes the original gas port look like an eliptical oval.
So now I am in the home stretch. The last part to install on the barrel now will be the front sight block once the gas port is drilled. The final steps will be to install the internal fire control components, and to await the replacement rear stock to do the final part of this build.
Stay tuned for that in the next blog post.