AR-15 front sight block removal

[NavyVet1959]

Around a year or two ago, I ordered off for an AR-15 10.5" barrel for a pistol that I was planned to build. Well, it's basically sat in the back of my gun safe all this time and I had forgotten about it, but I stumbled across it today while looking for something else and decided to see if I had enough parts on-hand to finish the project and if not, what I needed to order to complete it.

I figured that the first thing that I would do is install the barrel to the upper receiver and that is where I ran into a problem. The barrel came with a front sight block and if I install the gas tube, there there is no way to turn the barrel nut. I *think* I probably need to remove the front sight block, but it is pinned VERY WELL and all I ended up doing is bending my brass punch when I tried to knock the pins out of there. There is no seam underneath the front sight block, so I have to wonder if perhaps it was heated in order to expand it enough to install it on the barrel.

Any hints or suggestions would be appreciated.

[Cmm_3940]

The gas block pins are tapered. They come out from left to right, go in right to left. It can take a good deal of force to break the pins free; the factory finish is usually applied after the front sight housing is installed. Brownell's makes a bench block widget to make this job easier, but it really isn't needed, a piece of 2x4 scrap works just fine. It might take a few raps with a plastic hammer to knock the housing loose once the pins are removed.

[petroid]

the front sight base gas block is a slip fit over the barrel. It is held in place with a roll pin. You need to drive out the roll pin which will allow the sight base to slide off over the muzzle. It may be on pretty tight but shouldn't have required heating. a brass punch may not be strong enough. use a steel one just be careful not to let it slip off. use a hardwood or plastic mallet to drive the gas block off if it doesn't come off easy.

[country gent]

Those pins can be tight and some even used locktite on them for some unknown reason. Maybe getting it into a sloid vise and apply some heat to the area with the pins would help to loosen them. Use a punch with a close fitting nose and just long enough to get the pins out.

[montana_charlie]

I figured that the first thing that I would do is install the barrel to the upper receiver and that is where I ran into a problem. The barrel came with a front sight block and if I install the gas tube, there there is no way to turn the barrel nut.
If the barrel nut and everything is on the barrel, there is no need to remove the front sight base (or gas block, if that's what you have).
But you don't intall the gas tube until after the barrel is mounted.

There should be a pin that keeps the tube in the sight base / gas block, and that is all you need to mess with.
Remove the pin, remove the gas tube, and install the barrel.
Then, reinstall the gas tube and it's pin.

Do you have any condition that causes any of that to not compute?

Do you understand the torque specs for the barrel nut?

CM

[Grizzly Adams]

Use a steel starter punch(short taper,blunt end) to just break them loose, then a steel pin punch (straight shank), firm support for sight base, pins are tapered see above.

[Grizzly Adams]

YouTube is your friend 😍

[xacex]

YOu install the gas tube after you tighten the barrel nut on barrels that come pre fitted with the front sight, and barrel nut. Trust me, there is room to poke that tube into the receiver, and then wiggle it into the gas block. No need to take off the front sight unless you want to change it, or you want to do a free float. Some people just cut the sight where the gas tube goes in , and grind it down smooth. Add some paint, and you can put a free float tube over it. Thats the dirty way to make a low profile gas block. If you run into a problem I can walk you through it. Many of us on castboolits assemble these for fun. I wouldn't call it building until you start making your own receivers, and parts.

[freebullet]

use a nail set to start the pins coming out. they are tappered so they only come out one direction.

[NavyVet1959]

I'm using my phone with a 2G internet connection right now, so I cannot watch the YouTube videos. I finally get the gas tube in there, but it took some lube and quite a bit of wiggling. The upper I'm using is a flat top upper and as such, it might be questionable my use of a standard height front sight block, but that's what the barrel came with and I'm going to work with what I've got as much as possible before ordering off for more parts.

My .300 AAC pistol barrel came in today and it was what got me motivated to get off my *** and see if I had everything to finish the .223 / 5.56 pistol. I figured that I was going to need some parts, so the best way to determine what all I was going to need was to see how close I could get the .223 / 5.56 pistol to completion. One thing that I noticed though is the the gas port is a few inches further back on the .300 AAC barrel as compared to the .223 / 5.56 barrel. I suspect that the .223 / 5.56 barrel is using a carbine length gas tube. I'll probably just end up building a single lower and swapping it between the .223 /5.56 and .300 AAC uppers.

[NavyVet1959]

Turned out the wings on the front sight were just slightly too narrow for me to be able to screw down the front sight post after installing the detent and spring. Figured there were two solutions.



Take a dremel tool to it and grind a hair off of the inner portion of both wings
Spread the wings a bit



Since it aluminum, I was hesitant to bend it, but since it needed such a small amount of clearance and I didn't want to have to refinish the front sight block after grinding on it, I decided to try bending it. I took a 3/8" drill bit (which was slightly larger than the distance between the front sight wings) and positioned the shank of it parallel with the barrel, laying it in the the trough created by the wings of the front sight. I then placed this in my arbor press and gave it a bit of pressure. Couldn't see where it moved, but the front sight post screwed in with no problems afterwards and no marks on the finish of the front sight wings.

Oh well... Ran out of parts... So much for working with what I had on hand... Time to order some more parts...

[freebullet]

To stay legal you should have a lower setup as a pistol before making short barreled uppers unless you have a registered sbr.

[xacex]

To stay legal you should have a lower setup as a pistol before making short barreled uppers unless you have a registered sbr.

A stripped lower is sufficient unless you have a extra lower in the rifle configuration I wouldn't worry. Not having a stripped lower, or a rifle configured lower without an upper, or no lower and a completed rifle could get you ten years.

[NavyVet1959]

I have a lower that I'm planning on using for these two. My previous lower started out as a long barreled pistol (i.e. no stock), but eventually I added a stock to it and now it is configured as a rifle. It is my understanding of the ATF ruling that this is allowed as long as it did not start out as a rifle.

[freebullet]

It is my understanding you can go back to pistol yes. I just wanted you to be aware of the possible legal issues. Dont want you or a family member to get in hot water over a simple/avoidable technicality, even though your intent of building a pistol is documented.

I would not have an assembled short barreled upper without one of the following-
1. a virgin lower (or one never tied to a manufactured rifle)
2. a pistol lower
3. a registered sbr on hand

[NavyVet1959]

It is my understanding you can go back to pistol yes. I just wanted you to be aware of the possible legal issues. Dont want you or a family member to get in hot water over a simple/avoidable technicality, even though your intent of building a pistol is documented.

I would not have an assembled short barreled upper without one of the following-
1. a virgin lower (or one never tied to a manufactured rifle)
2. a pistol lower
3. a registered sbr on hand

Then I'm covered on 2 counts. My existing AR started life as a pistol, thus even though it is currently configured as a rifle, it can go back to being a pistol as long as I first remove the stock. I also have a couple of virgin lowers, one of these will be configured as a pistol for the .223 / 5.56 and .300 AAC uppers.

I'm not particularly inclined to go the SBR route. I don't like the wait... I don't like having to as permission of the government to do something that the Founding Fathers intended to be constitutionally protected... I don't like giving the government any more money than absolutely necessary... I don't like having to ask the government if I can take my firearm across state lines... I'll follow the ATF's *unconstitutional* rules as long as it is convenient to do so, but that's about it.

[xacex]

Get a SIG brace. It will solve the problem of sticking the buffer tube into your shoulder, and you can take it across borders without permission. No need for a SBR stamp with a SIG brace on the pistol my opinion. Try one, you might like it. I put off doing a SBR after trying one.

[NavyVet1959]

Get a SIG brace. It will solve the problem of sticking the buffer tube into your shoulder, and you can take it across borders without permission. No need for a SBR stamp with a SIG brace on the pistol my opinion. Try one, you might like it. I put off doing a SBR after trying one.

I've seen it and I'm considering it, but I want to see what the .300 AAC is like without it first before ordering it. Just got through ordering the BCG and pistol lower parts kit from PSA. I'm looking on eBay right now at some of the free float handguards to put on the .300 AAC pistol. The .223 /5.56 pistol came with the standard plastic handguard. Even though the barrels are the same length, the handguard would not work on the .300 AAC barrrel due to the fact that the gas port is further from the end of the barrel. Looks like I'll need something like a 4" handguard vs what appeared to be a 7" handguard for the .223 / 5.56 pistol.

EDIT: PSA was backed up on their orders and would not be able to get the items to me within the next 2 weeks, so I canceled the order and ordered from a different place.

[gew98]

If the barrel nut and everything is on the barrel, there is no need to remove the front sight base (or gas block, if that's what you have).
But you don't intall the gas tube until after the barrel is mounted.

There should be a pin that keeps the tube in the sight base / gas block, and that is all you need to mess with.
Remove the pin, remove the gas tube, and install the barrel.
Then, reinstall the gas tube and it's pin.

Do you have any condition that causes any of that to not compute?

Do you understand the torque specs for the barrel nut?

CM
This is it. You pop roll pin out for the gas tube. Put tube in a padded vise and pop upper ahile holding barrel...gas tube comes out. If you will be using a set of barrel vise blocks to change the barrel you should not have sight alignment issues. If you use an upper receiver block set you almost always have sight alignment issues which would require a 'tiny' shim to be made and inserted in between locator pin and it's slot on the clockwise side of the slot ( looking from muzzle end ) .