View Full Version : Installing Front sight gas block on a new barrel
I am wanting to place a front sight gas block on a 300 blackout barrel at the carbine length for a "Kino" setup. Barrel is setup with the standard pistol gas length as used by the 300.
My question is how install a "mock up" front sight gas block and taper pin it so you do not have a canted front sight? Is there a jig for this?
With the low profile gas block the jig goes off the gas port hole, and with this setup there would be no gas port hole to run a jig off of. The few low profile gas blocks I have installed, I have a jig for dimpling the barrels and once the gas block is on I have a jig to drill and install one tapered pin. Since the jig aligns off the gas port, it could technically be canted by a few degrees but with a low profile gas block it would not matter since it is covered by the rail.
So how does the gunsmiths align the front sight gas blocks?
Most gunsmiths don't do this because they don't have the tools. You will need an FSB alignment jig- http://www.brdengineering.com/. I think your best option is to send it to ADCO and have them do the FSB for you. Just slide your barrel nut and gas block into place before hand and then finish it once they send it back.
I am wanting to place a front sight gas block on a 300 blackout barrel at the carbine length for a "Kino" setup. Barrel is setup with the standard pistol gas length as used by the 300.
My question is how install a "mock up" front sight gas block and taper pin it so you do not have a canted front sight? Is there a jig for this?
With the low profile gas block the jig goes off the gas port hole, and with this setup there would be no gas port hole to run a jig off of. The few low profile gas blocks I have installed, I have a jig for dimpling the barrels and once the gas block is on I have a jig to drill and install one tapered pin. Since the jig aligns off the gas port, it could technically be canted by a few degrees but with a low profile gas block it would not matter since it is covered by the rail.
So how does the gunsmiths align the front sight gas blocks?
K.L. Davis
01-12-14, 14:57
Is this what you are trying to do? There are jigs out there... or you can fixture the barrel with the bore parallel to the mill table, then set the barrel index pin and a pin threaded in the front sight post hole at the same height as the bore CL - don't forget to account for half the width of the pins!
I also offer a complete barrel assembly, or I can drill and pin yours?
http://darkmountainresearch.com/designated_hitter/images/KINO300_2_WEB.JPG
Yes that is exactly what I am wanting. That jig is $150 and looks like a 6+ week wait for one so I am going to send it off to have done.
Adco will supply an fsb and pin it for $130, $90 if you send them your own fsb. +$15 for taper pins. I had them do an 11.5 barrel and built it up the same way.
Yes that is exactly what I am wanting. That jig is $150 and looks like a 6+ week wait for one so I am going to send it off to have done.
K.L. Davis,
With that rail on that upper, is there enough room on the end to thread a 51t AAC flash hider and run a SDN-6? Or does that rail hang over too far which would interfere with the can? I was wanting to put the DD 9.5 FPS rail on the Rainier Arms 10.5" barrel, but didnt know if there would be enough clearance for the can and mount.
Big question is what is the diameter of your barrel at the point to want to mount the FSB. A .750" FSB will be loose on .740" profiled barrel and my not take well to pinning. Maybe some milled flats and a set screws FSB would be better application.
Also, I would look into the clamp style FSB from Armalite. I had no problems with it mounted on a M4 barrel configured as a dissipator setup.
drarmament
01-16-14, 17:38
That is how I do it. Also when I was an instructor at apg that's how tough the students to do it
Reply for K.L Davis
The problem isn't mounting the fsb. It's getting it perfectly straight without any cant. I can mount it, drill the holes and install tapered pins. Just with out the jig, I can not get it perfectly straight. That's why I'm going to send it off.
I finally got around to getting all the parts together and was going to have member on here pin the FSB for me to guarentee it would not be canted.
I assembled it in a mock up configuration and discovered the DD lite II carbine cut out rail is about 1/2" too long for the Rainier arms 10.5" barrel I have and it will not allow my SDN-6 to tighten on the QD attachment.
So just let let everyone know the DD lite II rail carbine cutout will not work with a 10.5" barrel if you will be using a suppressor.
Looks like the only two rails that are short enough for the 10.5" barrel is the Centurion C4 cut out (9.5" length) and the REV Free float cutout (9.23" length). Hopefully that little info will save someone some heartache.
My next problem is where the "false" FSB will be attaching at carbine length on the barrel it is a .742" diameter.
I am worried about the FSB being loose even after it is pinned.
What are my options beside a clamp on FSB?
I hate to couture the barrel to a .625" and use the small FSB.
My next problem is where the "false" FSB will be attaching at carbine length on the barrel it is a .742" diameter.
If my math is correct, that's .008" too thin... and WAY too much smaller than the .750" that it should be.
In order to use standard parts, the barrel needs a specific profile to do this, namely .750 or .625 journals at both of the normal locations.
What are my options beside a clamp on FSB?
Scrap the build.......
Robb Jensen
12-10-14, 10:32
For a few customers of ours and some employees WAR Rifles in Manassas Park VA has done this. I don't know what they charge but they use and old Bridgeport mill which has digital readouts on it.
If my math is correct, that's .008" too thin... and WAY too much smaller than the .750" that it should be.
Where the low profile gas block is (pistol length), the barrel is the correct .750" and is a tight fit. It's pinned there.
But where the "false" fsb (carbine length) is, the barrel has a step down to .742".
Ill known if its a hack job on my part if this ends up being posted in the Gunsmithing Hall of Shame thread. ;)
I finally finished this gun tonight.
I had to do I little fabricating to get what I wanted (pinned FBS, and not a clamp on).
First I cut off the sling mount and bayo lug with a band saw. I left about 1/16" on the FSB so not to chew it up with teh band saw. Then I used the 6x48" belt sander and smoothed it flush. I finished it off with a blue roloc buffing pad and gave it a slick finish.
http://i43.photobucket.com/albums/e400/rhino4x4/Guns/7FAD567C-34F2-49A1-820D-43B51F9BEBC0.jpg (http://s43.photobucket.com/user/rhino4x4/media/Guns/7FAD567C-34F2-49A1-820D-43B51F9BEBC0.jpg.html)
Now since the inside diameter was .750 on the FSB and the barrels outside diameter was .742 I was worried about the Front sight being canted so this is where I had to downside the ID of the FSB. Two MIG welds on the inside
http://i43.photobucket.com/albums/e400/rhino4x4/Guns/B88F6595-EBAE-4F04-9040-B01B2FAF7397.jpg (http://s43.photobucket.com/user/rhino4x4/media/Guns/B88F6595-EBAE-4F04-9040-B01B2FAF7397.jpg.html)
Then I used the hand file to smooth out the spot welds and to make it fit perfect.
http://i43.photobucket.com/albums/e400/rhino4x4/Guns/120B6FFA-75CD-41E5-82C3-142252E64A46.jpg (http://s43.photobucket.com/user/rhino4x4/media/Guns/120B6FFA-75CD-41E5-82C3-142252E64A46.jpg.html)
I painted the FSB with high temp engine paint and heat treated the FSB for a more durable finish. This FSB was a very tight fit on the barrel. Since I didn't have the FSB jig, I sent it to W.A.R. Rifles per Rob Jensen's post and they pinned the FSB perfectly.
http://i43.photobucket.com/albums/e400/rhino4x4/Guns/48CA2167-C1FD-45EC-A6D8-B749709C3642.jpg (http://s43.photobucket.com/user/rhino4x4/media/Guns/48CA2167-C1FD-45EC-A6D8-B749709C3642.jpg.html)
http://i43.photobucket.com/albums/e400/rhino4x4/Guns/575CAD35-8D29-46F5-A941-308A77AF9134.jpg (http://s43.photobucket.com/user/rhino4x4/media/Guns/575CAD35-8D29-46F5-A941-308A77AF9134.jpg.html)
http://i43.photobucket.com/albums/e400/rhino4x4/Guns/1E10938C-7BA1-49A8-BE77-51BAD99E5F42.jpg (http://s43.photobucket.com/user/rhino4x4/media/Guns/1E10938C-7BA1-49A8-BE77-51BAD99E5F42.jpg.html)
When I told Greg at WAR rifles about the spot welds to tighten up the ID he said he was first leery because of some work he has seen customers do before, but once he got the parts in he said everything fitted together perfectly. Thanks goes to the guys at WAR rifles for the great pin job.
Not paying attention never mind.
Lostinthewoods
01-29-15, 21:50
Why didn't you put the weld spots on the bottom of the fsb instead of on the top by the gas port?
You're probably going to have a huge gas leak from the gas port.
It probably would have worked fine if you'd have placed the spots on the bottom.
.46caliber
01-29-15, 21:56
Why didn't you put the weld spots on the bottom of the fsb instead of on the top by the gas port?
You're probably going to have a huge gas leak from the gas port.
It probably would have worked fine if you'd have placed the spots on the bottom.
Re-read thread. The FSB is not the functioning gas block. It is only being used as a sight.
Sent from my Nexus 4 using Tapatalk
The problem isn't mounting the fsb. It's getting it perfectly straight without any cant. I can mount it, drill the holes and install tapered pins. Just with out the jig, I can not get it perfectly straight. That's why I'm going to send it off.
I realize you finished it, but wanted to comment on one aspect of the project. I recently did one. Nobody close by had a jig. After removing the sling loop and rivet I drilled and tapped the hole between the sling mount ears to 10-32, and used a set screw. I got it as close by eyeball as I could, and used some red loc tite around the edges and in the pin holes to help hold it in place. I avoided the area near the gas port. I centered the rear sight, and shot it. It was off a little. I loosened the screw and moved it a bit (takes a little effort with the loc tite), finally getting it fairly well centered after two tries. I shot it at 300 yards plinking at rocks, it was a few clicks off from perfect center, but fairly close. Had a friend with a mill drill the pin holes and ream them, then install the pins. Removed the set screw, put the sling loop back on, and it shot good.
I dont know how it would work with a folding rear sight, mine was an A-2 carry handle upper.
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