First rail chop - Page 1

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Posted: 7/12/2024 4:47:21 PM EST

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.

Posted: 7/12/2024 5:03:02 PM EST

[#1]

Posted: 7/12/2024 5:07:10 PM EST

[#2]

Impressive work

Posted: 7/12/2024 5:08:37 PM EST

[#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

Posted: 7/12/2024 5:20:56 PM EST

[#4]

Quote History

Quoted:
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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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.

Posted: 7/12/2024 7:32:38 PM EST

[#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?

Posted: 7/12/2024 8:12:34 PM EST

[#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

Posted: 7/12/2024 8:34:50 PM EST

[#7]

Quote History

Quoted:

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.

View Quote

ty, kinda what I figured

Posted: 7/12/2024 10:09:00 PM EST

[#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.

Posted: 7/13/2024 6:58:03 PM EST

[#9]

Quote History

Quoted:
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?

View Quote

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.

Posted: 7/13/2024 7:00:58 PM EST

[#10]

Quote History

Quoted:
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.

View Quote

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.

Posted: 7/14/2024 12:22:48 AM EST

[#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

Posted: 7/14/2024 9:42:01 AM EST

[#12]

Quote History

Quoted:
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

View Quote

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.

Posted: 7/14/2024 10:09:45 AM EST

[#13]

Quote History

Quoted:
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.

View Quote

In the pin location? I'll have to look. I could shorten an Allen wrench pretty easily to maybe tuck in there

Posted: 7/14/2024 11:26:51 AM EST

[#14]

Quote History

Quoted:
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

View Quote

Nice work.

I did the same thing when I put together my first chopped rail.

6-32x0.75 set screws were used.

Posted: 7/14/2024 11:48:21 AM EST

[#15]

Quote History

Quoted:
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

View Quote

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.

Posted: 7/14/2024 1:57:47 PM EST

[#16]

Quote History

Quoted:

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.

View Quote

I'm leaning towards this and hiding with rail covers.

ETA: thanks!

Posted: 7/14/2024 2:02:25 PM EST

[#17]

Quote History

Quoted:
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

View Quote

Thanks! That looks awesome!

Posted: 7/14/2024 8:24:03 PM EST

[#18]

Quote History

Quoted:

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.

View Quote

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

Posted: 7/14/2024 9:04:21 PM EST

[#19]

Quote History

Quoted:
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

View Quote

@M4ger and @s4s4u

Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws?

Posted: 7/14/2024 9:10:07 PM EST

[#20]

Quote History

Quoted:
@M4ger and @s4s4u

Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws?

View Quote

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...

Posted: 7/14/2024 9:10:15 PM EST

[#21]

Quote History

Quoted:

Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws?

View Quote

That's how many do it.

Milling flats into the barrel for the set screws to contact has worked best IME.

Posted: 7/14/2024 9:13:18 PM EST

[#22]

Quote History

Quoted:
@M4ger and @s4s4u

Are you guys just drilling straight through the FSB, tapping all the way through, then installing 4 set screws?

View Quote View All Quotes

View All Quotes

Quote History

Quoted:

Quoted:
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

@M4ger and @s4s4u

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.

Posted: 7/14/2024 9:18:15 PM EST

[#23]

Great info here by a fellow Arf member:

https://acatholicmechanic.blogspot.com/2016/02/diy-a2-front-sight-base-install.html?m=1

Posted: 7/25/2024 2:00:07 PM EST

[#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.

Posted: 7/25/2024 5:03:10 PM EST

[#25]

Quote History

Quoted:
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

View Quote

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.

Posted: 7/25/2024 5:28:36 PM EST

[#26]

Quote History

Quoted:

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.

View Quote

Thanks! I haven't on any of my chopped rails to date. The below cut is close to 3 years old, but it is clean and smooth so it doesn't bother me. However, I think I want to on this rail since there a multiple cuts, etc. I may try a model brush with some different greens and see what blends the best.