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MT, USA
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Posted: 7/12/2024 5:47:21 PM EDT
[Last Edit: CORDrew]
I decided to try chopping a rail for a FSB. I'm really pleased how it turned out and the process was not bad. It took a few hours of careful work. I went slow but it still isn't perfect. There are some small asymmetries on the chop, but pretty minor, and totally acceptable to me for the first try. This build started because I had an unused barrel with an FSB, and saw a guy on instagram (ultraviolentiamextrema) post a similar build.
I did the chop with a hack saw, dremel, and files. Went slow and measured several times. Painted the raw aluminium with "camo" flat black rattle can. Build details are: 16" mid BA pencil barrel 13" Troy Alpha rail Bushmaster Police Trade in lower with B5 coyote grip and 2 stage Schmid trigger swap Still deciding on optics.     |
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Posted: 7/12/2024 6:03:02 PM EDT
[#1]
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Posted: 7/12/2024 6:07:10 PM EDT
[#2]
Impressive work
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Posted: 7/12/2024 6:08:37 PM EDT
[#3]
I've always been curious about how ya get the frank above the beans? Do you unpin the fsb and slide it on with the rail
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MT, USA
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Posted: 7/12/2024 6:20:56 PM EDT
[Last Edit: CORDrew]
[#4]
Quote HistoryOriginally Posted By weapons_free: I've always been curious about how ya get the frank above the beans? Do you unpin the fsb and slide it on with the rail Yes, here's how I did it. Unpin the FSB from the barrel. Spin the FSB for about 10 minutes with lots of lube so it slides on and off easy. Cut the bayonet lug and sling point off of the FSB. Cut the rail. Lots of small adjustments (grinder and files) and test fitting here. Paint. Barrel nut on like usual. Gas tube in the upper and slid as far back as possible. Put the FSB in the rail, through the cut. Slide the rail and FSB on the barrel, as a unit. Mess around with the rail until you can drive in the FSB taper pins through the existing holes in the rail. Tighten the rail like usual. Slide the gas tube into the gas block and pin. Flash hider on. Done. I tested each step and made adjustments prior to final assembly. Not counting paint drying, it took about 4 hours all in. |
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MN, USA
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Posted: 7/12/2024 8:32:38 PM EDT
[#5]
Looks good. Personally, I would have squared off the cut to remove the crescent leftovers even if it made the pocket larger, but....
 Are you planning on using a fixed rear to take advantage of that barrel mounted fixed front? |
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MT, USA
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Posted: 7/12/2024 9:12:34 PM EDT
[#6]
Nice! I've chopped many rails for length, but I'm about to do my first FSB pocket on Mk16 with an A2 upper
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Posted: 7/12/2024 9:34:50 PM EDT
[#7]
Quote HistoryOriginally Posted By CORDrew: Yes, here's how I did it. Unpin the FSB from the barrel. Spin the FSB for about 10 minutes with lots of lube so it slides on and off easy. Cut the bayonet lug and sling point off of the FSB. Cut the rail. Lots of small adjustments (grinder and files) and test fitting here. Paint. Barrel nut on like usual. Gas tube in the upper and slid as far back as possible. Put the FSB in the rail, through the cut. Slide the rail and FSB on the barrel, as a unit. Mess around with the rail until you can drive in the FSB taper pins through the existing holes in the rail. Tighten the rail like usual. Slide the gas tube into the gas block and pin. Flash hider on. Done. I tested each step and made adjustments prior to final assembly. Not counting paint drying, it took about 4 hours all in. ty, kinda what I figured
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Posted: 7/12/2024 11:09:00 PM EDT
[#8]
Nicely done.
Imagine it wasn't easy to strike the head of the taper pins through the holes in the handguard. Did you leave the handguard loose or tighten it in it's final location before smacking the pins? I typically use the corner of a vise to press them in, but that wouldn't be possible in this situation. |
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MT, USA
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Posted: 7/13/2024 7:58:03 PM EDT
[#9]
Quote HistoryOriginally Posted By s4s4u: Looks good. Personally, I would have squared off the cut to remove the crescent leftovers even if it made the pocket larger, but.... https://i.giphy.com/media/v1.Y2lkPTc5MGI3NjExZTJxZXp3MXdwbWxycWhudjNycHplcnkydWpia2M1NGNjYWZ3ang5cCZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/JvviEn6B5FBgGR6QEv/giphy.gif Are you planning on using a fixed rear to take advantage of that barrel mounted fixed front? Thanks, yea I thought about squaring and cutting off the "nubs". I thought it might look better with a smaller pocket but would be equally functional either way. I'm probably going to do another one with one of the Geissele blems I just ordered and I'll try to make that one look smoother. Yes, I'm planning a fixed rear. Probably the Midwest fixed combat rear. Or maybe a Daniel Defense. I have a couple of the Midwest sights on other rifles and they're solid. It'll get a red dot too. |
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MT, USA
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Posted: 7/13/2024 8:00:58 PM EDT
[#10]
Quote HistoryOriginally Posted By Blowout: Nicely done. Imagine it wasn't easy to strike the head of the taper pins through the holes in the handguard. Did you leave the handguard loose or tighten it in it's final location before smacking the pins? I typically use the corner of a vise to press them in, but that wouldn't be possible in this situation. Not bad honestly. I left the rail loose and had to rotate it and slide it forward a bit to line up the holes with the FSB taper pins. Then I braced the barrel and the FSB on wood blocks, and put padding under the rail and upper receiver. Then pounded them in. |
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MT, USA
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Posted: 7/14/2024 1:22:48 AM EDT
[Last Edit: spyderboy03]
[#11]
Got mine mocked up tonight. Tapped the hole in the FSB for a set screw to hold it for now. Haven't had the FSB or barrel drilled for taper pins yet, and there will be no way that I see to install them, unless I remove the anti rotation tabs. May be able to get away with removing the top tabs and reducing the set screw tabs and still get those to line up the rail and be anti rotation. Otherwise, I guess drill and tap the front of the FSB for a set screw and dimple the barrel. Could also do a combo of remove tabs and make partial pin holes in the side of the rail...
ETA: this is a .625 barrel/FSB  |
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MN, USA
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Posted: 7/14/2024 10:42:01 AM EDT
[#12]
Quote HistoryOriginally Posted By spyderboy03: Got mine mocked up tonight. Tapped the hole in the FSB for a set screw to hold it for now. Haven't had the FSB or barrel drilled for taper pins yet, and there will be no way that I see to install them, unless I remove the anti rotation tabs. May be able to get away with removing the top tabs and reducing the set screw tabs and still get those to line up the rail and be anti rotation. Otherwise, I guess drill and tap the front of the FSB for a set screw and dimple the barrel. Could also do a combo of remove tabs and make partial pin holes in the side of the rail... https://i.imgur.com/EObtyU3.jpg Can you get an Allen wrench in there? I typically use setscrews instead of taper pins when I install a FSB on a new barrel. |
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MT, USA
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Posted: 7/14/2024 11:09:45 AM EDT
[#13]
Quote HistoryOriginally Posted By s4s4u: Can you get an Allen wrench in there? I typically use setscrews instead of taper pins when I install a FSB on a new barrel. |
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Posted: 7/14/2024 12:26:51 PM EDT
[#14]
Quote HistoryOriginally Posted By spyderboy03: Got mine mocked up tonight. Tapped the hole in the FSB for a set screw to hold it for now. Haven't had the FSB or barrel drilled for taper pins yet, and there will be no way that I see to install them, unless I remove the anti rotation tabs. May be able to get away with removing the top tabs and reducing the set screw tabs and still get those to line up the rail and be anti rotation. Otherwise, I guess drill and tap the front of the FSB for a set screw and dimple the barrel. Could also do a combo of remove tabs and make partial pin holes in the side of the rail... ETA: this is a .625 barrel/FSB https://i.imgur.com/EObtyU3.jpg Nice work. I did the same thing when I put together my first chopped rail. 6-32x0.75 set screws were used.    
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MT, USA
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Posted: 7/14/2024 12:48:21 PM EDT
[#15]
Quote HistoryOriginally Posted By spyderboy03: Got mine mocked up tonight. Tapped the hole in the FSB for a set screw to hold it for now. Haven't had the FSB or barrel drilled for taper pins yet, and there will be no way that I see to install them, unless I remove the anti rotation tabs. May be able to get away with removing the top tabs and reducing the set screw tabs and still get those to line up the rail and be anti rotation. Otherwise, I guess drill and tap the front of the FSB for a set screw and dimple the barrel. Could also do a combo of remove tabs and make partial pin holes in the side of the rail... ETA: this is a .625 barrel/FSB https://i.imgur.com/EObtyU3.jpg Looks awesome! Personally, I'd drill some holes in the handguard and run taper pins. I like the bombproof FSB/taper pin combo. But I'm sure that set screws would work well 99.9% of the time. |
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MT, USA
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Posted: 7/14/2024 2:57:47 PM EDT
[Last Edit: spyderboy03]
[#16]
Quote HistoryOriginally Posted By CORDrew: Looks awesome! Personally, I'd drill some holes in the handguard and run taper pins. I like the bombproof FSB/taper pin combo. But I'm sure that set screws would work well 99.9% of the time. ETA: thanks! |
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MT, USA
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Posted: 7/14/2024 3:02:25 PM EDT
[#17]
Quote HistoryOriginally Posted By M4ger: Nice work. I did the same thing when I put together my first chopped rail. 6-32x0.75 set screws were used. https://live.staticflickr.com/7283/16747485971_0b963a8125_h.jpg https://live.staticflickr.com/8697/16641386673_cfaac8c116_h.jpg https://live.staticflickr.com/8785/16641385633_2325e26316_h.jpg https://live.staticflickr.com/1638/24831572075_5bcdcdae57_h.jpg |
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MN, USA
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Posted: 7/14/2024 9:24:03 PM EDT
[#18]
Quote HistoryOriginally Posted By CORDrew: Looks awesome! Personally, I'd drill some holes in the handguard and run taper pins. I like the bombproof FSB/taper pin combo. But I'm sure that set screws would work well 99.9% of the time. You are not wrong. But, I have beaten the crap out of setscrewed FSB's and not lost POI. Set screws are a lot easier to lock in the front sight indexing as well, and as a bonus you will have a drift adjustable FSB if you mess that up. A mini-maglight and a plumb line make that easy-peasy tho 
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MT, USA
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Posted: 7/14/2024 10:04:21 PM EDT
[#19]
Quote HistoryOriginally Posted By s4s4u: You are not wrong. But, I have beaten the crap out of setscrewed FSB's and not lost POI. Set screws are a lot easier to lock in the front sight indexing as well, and as a bonus you will have a drift adjustable FSB if you mess that up. A mini-maglight and a plumb line make that easy-peasy tho Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws? |
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MN, USA
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Posted: 7/14/2024 10:10:07 PM EDT
[#20]
Quote HistoryOriginally Posted By spyderboy03: @M4ger and @s4s4u Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws? What actually works best is take-off FSB's that have already been reamed. You just run a drill bit through the holes to conform them and then tap. With a new FSB you will get deflection when you drill it unless you use a filler rod that is the same diameter as the inside of the FSB. Don't ask me how I know... 
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Posted: 7/14/2024 10:10:15 PM EDT
[#21]
Quote HistoryOriginally Posted By spyderboy03: Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws? That's how many do it. Milling flats into the barrel for the set screws to contact has worked best IME. |
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Posted: 7/14/2024 10:13:18 PM EDT
[#22]
Quote HistoryOriginally Posted By spyderboy03: @M4ger and @s4s4u Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws? Quote HistoryOriginally Posted By spyderboy03: Originally Posted By s4s4u: You are not wrong. But, I have beaten the crap out of setscrewed FSB's and not lost POI. Set screws are a lot easier to lock in the front sight indexing as well, and as a bonus you will have a drift adjustable FSB if you mess that up. A mini-maglight and a plumb line make that easy-peasy tho Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws? So the 2 times I did this, the FSB was already taper pinned on. I removed the front pin, tapped it, installed the set screw to see if I needed to tap further, and repeated until I was happy with the placement. Then I'd remove the rear taper pin, closest to the gas port, and tap that one while the front was secure.  The gas tube was floating inside the handguard and would be pinned to the FSB before putting everything onto the barrel nut and barrel. The screws would only remove from the ejection port side. |
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Posted: 7/14/2024 10:18:15 PM EDT
[#23]
Great info here by a fellow Arf member:
https://acatholicmechanic.blogspot.com/2016/02/diy-a2-front-sight-base-install.html?m=1 |
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MT, USA
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Posted: 7/25/2024 3:00:07 PM EDT
[Last Edit: spyderboy03]
[#24]
Got the FSB taper pinned and installed. Definitely a pain and definitely a few things I might do differently if I did it again. The back pin cutout is the first one I did and I didn't realize how high up in to the meat of the rail the FSB was. I adjusted for the front hole and got it closer to where it needed to be. I'll likely pick up some rail covers and it will hide the holes.
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MT, USA
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Posted: 7/25/2024 6:03:10 PM EDT
[#25]
Quote HistoryOriginally Posted By spyderboy03: Got the FSB taper pinned and installed. Definitely a pain and definitely a few things I might do differently if I did it again. The back pin cutout is the first one I did and I didn't realize how high up in to the meat of the rail the FSB was. I adjusted for the front hole and got it closer to where it needed to be. I'll likely pick up some rail covers and it will hide the holes. https://i.imgur.com/M6PH7Xk.jpg https://i.imgur.com/17CN50U.jpg I think it looks awesome and will be a great rifle. Are you planning to do anything the color the raw aluminum at the cuts? I'm going to cut a DDC (brown) geissele rail but haven't decided how to deal with coating/coloring the raw cut. |
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MT, USA
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Posted: 7/25/2024 6:28:36 PM EDT
[#26]
Quote HistoryOriginally Posted By CORDrew: I think it looks awesome and will be a great rifle. Are you planning to do anything the color the raw aluminum at the cuts? I'm going to cut a DDC (brown) geissele rail but haven't decided how to deal with coating/coloring the raw cut.  |
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PA, USA
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Posted: 7/25/2024 8:19:54 PM EDT
[#27]
Nice job!
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Posted: 7/26/2024 11:08:33 PM EDT
[#28]
Looks good
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VA, USA
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Posted: 7/29/2024 2:12:39 PM EDT
[#29]
Nice. I cheated and chopped a Midwest 2 piece fsp cutout free float rail down for a 10.5 mk18ish build.
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