clearance between free float rail and shaved FSB

[Androctonus]

Hello everyone. I got the FSB on my Colt 6920 shaved down and put a free float rail over the gas block. The gunsmith didn't shave the FSB down as far as he could. At the least, I can barely stick a 0.030" feeler gauge between the side of the gas block and the rail. There's more clearance on the other sides, as well as top and bottom. Is that going to be enough free float clearance when the M4 profile barrel whips under fire? The gunsmith refuses to shave the gas block any further.

[mark5pt56]

It will hit the rail. I don't know what rail you have, options are another rail, shave down the fsb down yourself or a lower block. Common issue with some rails that are a wee bit narrow. Did he have the rail available when shaving?

Know for a fact that the clearance on the Centurion rifle is more than that and it will pop their brand of panels off, I had to move them. I've also had to shorten a Magpul screw on another brand.

[Iraqgunz]

Utilizing that now famous method from the French inventor Joseph Nicéphore Niépce and posting it here would greatly assist us in giving you an answer. It would also help to know which rail, as mark5pt56 mentioned.

Hello everyone. I got the FSB on my Colt 6920 shaved down and put a free float rail over the gas block. The gunsmith didn't shave the FSB down as far as he could. At the least, I can barely stick a 0.030" feeler gauge between the side of the gas block and the rail. There's more clearance on the other sides, as well as top and bottom. Is that going to be enough free float clearance when the M4 profile barrel whips under fire? The gunsmith refuses to shave the gas block any further.

[GH41]

I don't think knowing what rail he has matters. He either needs less gas block or more room. 30 thou isn't near enough room IMO.

[Androctonus]

It’s a narrow BCM MCMR handguard. The gunsmith had it when shaving the gas block. I’d consider getting another rail if I didn’t like the MCMR so much. I’ve searched the forums and have seen 1/16th of an inch minimum clearance said several times. But, someone said 1/32 per side for 1/16th total, so I thought I’d ask. 0.030” is almost 1/32 (0.031”).

[grizzman]

If you like the BCM handguard, then the best solution is to shave the FSB further. I wouldn't use that gunsmith again.

[Androctonus]

Utilizing that now famous method from the French inventor Joseph Nicéphore Niépce and posting it here would greatly assist us in giving you an answer. It would also help to know which rail, as mark5pt56 mentioned.

Here's the best I could do, Iraqgunz. It's the top right of the gas block under the handguard's pic rail. The photo makes it look a little worse than it is.FSB.jpg

[justin_247]

Deleted.

[Androctonus]

Deleted

[mark5pt56]

By the looks of it, you need your money back on that hack job, is it even refinished? Take the rail off and if you have files or a Dremel to clean it up. I don't know what he charged, but this may be easier for you https://www.opticsplanet.com/midwest...r-lpg-750.html
It covers the "front sight base scar" if that's important. I do know it will go under the MI rail of course. I used that on a BCM that has a FSB, red loctite on the screws(3) and ran at least 6-7k on it hard without issue.