Ok so this is a centurion c4 10" rail going on a LMT 10.5 upper I want to shave the bayo lug and mill the rail to leave the FSB intact. I wanted to just make sure their isnt something Im missing that will come back and bite me later. I could shave the FSB and leave the rail as is but would prefer a full FSB . Let me know what you think.
Why don’t you just use the C4 Carbine Cutout rail?
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If you screw up your modification, which is more costly to replace?
Cut the FSB first. If you don’t like it, get a new FSB and modify the rail. Provided you have a rail mounted front iron on hand to test with.
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Because I have this one already from something else.
You can’t just get a new FSB.
Thanks. Now I feel like a boob. Off to read up on FSBs.
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if you were doing it on the cheap your better off shaving the FSB, if not just buy a gas block. DD makes a nice fixed front sight if that’s what you are going for.
If I wanted to keep the FSB, I’d go ahead and cut a slot in the handguard. Of course, I’m used to cutting metal and hand fitting parts, so to me it’s no big deal
If you shave the FSB then you’d spend another 60ish bucks on a front sight. Cut the rail! FSB cut outs are awesome. You cant beat the durability of a taper pined fsb. I’m about to cut-out a NSR rail (inspired by 2nd.amendment).
If you absolutely must keep that rail then your best option is going to be getting a low profile gas block. Then you can use a front sight mounted to the rail. If you mill the rail for the FSB you’ll still have a f’d up front sight base and f’d up rail. You’re going to have to refinish the milled areas of both and it will look wonky.
I’d just sell that rail on the EE and order one with the FSB cutout from the factory.
I think he means because you can’t pin the new one using the existing hole on the barrel. The FSB is installed and then pinned so each FSB/barrel combo are basically mated to eachother.
I have shaved, altered many rails in my time and have done the exact thing you want to do more times then I can count, since long before cutout rails were produced. Not difficult to accomplish.
Thanks for the plug. However, I have both shaved and non shaved FSP. I just happen to have extra. It is really up to you and if you want to run fixed front sight like the DD or run the Troy flips up all the time if you want the option later down the road.
nice work there mattexass
How will he have a jacked up FSB? The only thing he’ll be cutting there is the lug and sling loop. A little touch up of cold blue will take care of that. If he cuts the handguard, he can touch it up with a little alumablack and make it fit the FSB the way he wants it to
FSB shave is easy to do. I highly recommend it.
There’s your answer. 
I understand the hesitation of cutting an expensive rail, but cost aside, rails are replaceable. No turning back once you shave your FSB.
I second this course of action. While expensive, you can fix a mess up on a rail.
https://www.m4carbine.net/showthread.php?t=135657
And sell yours to him
Win win win!