Has anyone expended the effort to modify a free float handguard (ie, Centurion or ALG are my go-to) by cutting back the front or cutting out a space from the top for a FSB? Additionally, would there be concerns about the structural integrity of the handguard afterward?
I thought I’d seen this done by someone before. I understand it is not necessary. However, I really like FSB’s and would like to utilize them with longer slim, free float MLOK/Keymod handguards.
Years ago I had a buddy notch out a cheap YHM FF tube for a 16" carbine with the FSB.
It was a range toy so I never abused it or used it for anything tough so I can’t comment or durability, the biggest problem that I completely overlooked before starting was how much of a PITA it would be to reinstall the FSB pins. Holes had to be cut in the rail for punch access and I would likely not do it again. Sorry I couldn’t answer your durability question but figured it was worth mentioning the FSB pins in-case, like me, you overlooked it.
I want to say someone here did it to a Fortis handguard and I vaguely remember an ALG but that might’ve been on another site.
The only thing I can think of on cutting it behind the fsb is if the cut ends up in the middle of a slot it would screw up the forward most mount slot and might be something of a snagging issue.
i actually did this for a friend with a yhm rail 
i’m notching out the rail on my leonidas to accommodate a switchblock at the moment. i now know why noveske went with a split rail on their switchblock rifles. making the switchblock work on a one piece free float rail was a bit of a challenge.
Beautiful. What did you use to cut it out? I
I have cut off an Aero hand guard and one Geissele, but not for use with a FSB. I just wanted a length in between what is manufactured. I’ve had no problems.
ALG EMR V1 MLOK
BCM 12.5” Kino
I’m not a machinist… But it looks like it would be simple enough to cut back the 10” rail to fit my upper.
Or, judging by what is shown on the YHM, it should be possible to cut out a section of of the 12” EMR V2:
V0 is dirt cheap right now and has the least amount of slots milled into it.
Maybe a good option to try?
The EMRs are small inside diameter though, might have to chop off the bayo lug and sling stud ears.
I’ve kept an thread on this exact topic bookmarked for quite some time:
https://www.m4carbine.net/showthread.php?128947-Custom-Noveske-14-5s-hacking-up-some-NSRs
I have personally modified 2 KAC URX4 MLOK rails, ill post pics later, I haven’t had any problems. I machined the MLOK groves longer on both to secure gas block and I cut a 13 rail down to 10.75".
Well, now I know it’s been done. Those look great. I come back to wondering about durability, cutting off the top rail that seems to provide much of the mass.