My friend Chuck the vet's M&P 15 came with a fixed front sight. I put on a Diamondhead VRS handguard that I had that wasn't a free-float, so it was a direct replacement for his fore-end without rails. I also installed a low gas block that I had. The manufacturer said it would work in the place of a standard A2 front sight, including with the use of the fore-end cap. It didn't mate up exactly, apparently, because the gun didn't reliably cycle. The gas hole must've been just a bit off. It looked ok, but it used set screws instead of taper pins, and it had to be the reason for some failures to feed. If I had a free-floated handguard I would've used it, but I was trying to save him some money. A floated handguard would've given me the extra sliver of room I needed. As it was, I pushed the low-profile gas block tightly against the handguard cap like the manufacturer said, and it didn't work.
By the way, the most important tool to remove a factory tapered-pin sight is a baby sledge. And sometimes they are tight, and I mean beat the living crap out of it tight. This one certainly was. Make sure you have a solid, non-marring rest for the barrel and upper, and use good punches. Cheap ones will bend immediately. Use tape for scratch protection, and hold the punch with vice-grips until the pins start to move. Then they come right out.
Anyway, I decided to chop the top off his factory A2 sight and reinstall it with the taper pins I prefer. After a smashed finger and bird cage removal it slipped off again just fine. I put it on my band saw with the proper height rest for a straight cut, and the darn thing wouldn't cut worth a darn. And I didn't have another blade.
So, plan two. Whip out the old Dremel with reinforced cutting discs and a good vice. Those discs will cut anything. That disc just walked through that hard metal like nothing. I wanted to use the band saw for a straight cut and less sanding and grinding, but it only took a few extra minutes with power tools, and it turned out very good after a few light swipes with a file.
I sprayed it with some high heat paint and reinstalled it with his Nikon 1.5-6 illuminated M-223, my favorite scope of last year, and our 2014 product of the year. Really a superb product. It's resting nicely in a 30mm non-QD Burris PEPR mount. I boresighted it with our OPMOD boresight, then matched the green laser from his LaserMax Unimax to the red illuminated dot in his Nikon Scope. The Unimax is installed on a Diamondhead accessory rail on the right side of his fore-end. The left side rail holds an easily detachable Streamlight Game Spotter with remote, and the lower rail has on it a GG&G bipod adapter and is for his Champion Targets Pivot Bipod. This is my current favorite all-around bipod. It swivels and pans and rotates and locks easily. It's light enough, sturdy, and reasonably priced.
Chuck sighted in his gun and laser and it ran like a champ. It shoots very well helped a lot by his CMC trigger.