clearance between free float rail and shaved FSB

**slimedog** · 04-07-19, 16:34

A pinned, shaved down FSB is a pretty much the most robust gas block you can get, and I wouldn't replace it. Having cut down several FSBs myself (in exactly the way shown in the youtube video below), I suggest using a dremel or small grinding wheel (I think the dremel is a better option since you don't need to remove much and it'll be easier to control) to remove material until you have enough clearance. Then cold blue the parts you made shiny. Here are some links:

https://www.youtube.com/watch?v=5sBqDpi-Cb4
https://www.brownells.com/gunsmith-t...nt=167-008-200

Finally, I don't think it's necessary to remove it from the barrel (taper pins can be a bear to get out). Just take the rail off and go to town on the high parts of the gas block. Getting it a warm won't hurt - gas block get pretty hot during use. Just be careful not to hit the gas tube or the barrel with the dremel...

Good luck!

**GH41** · 04-07-19, 17:28

Originally Posted by slimedog

A pinned, shaved down FSB is a pretty much the most robust gas block you can get, and I wouldn't replace it. Having cut down several FSBs myself (in exactly the way shown in the youtube video below), I suggest using a dremel or small grinding wheel (I think the dremel is a better option since you don't need to remove much and it'll be easier to control) to remove material until you have enough clearance. Then cold blue the parts you made shiny. Here are some links:

https://www.youtube.com/watch?v=5sBqDpi-Cb4
https://www.brownells.com/gunsmith-t...nt=167-008-200

Finally, I don't think it's necessary to remove it from the barrel (taper pins can be a bear to get out). Just take the rail off and go to town on the high parts of the gas block. Getting it a warm won't hurt - gas block get pretty hot during use. Just be careful not to hit the gas tube or the barrel with the dremel...

Good luck!

I love the guy but that video was painful to watch! Holding it with the rag is asking for a painful manicure. The kind that requires an ER visit to fix.

**Iraqgunz** · 04-07-19, 17:34

Not enough room based on what?

Originally Posted by 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.

**Iraqgunz** · 04-07-19, 17:37

That picture doesn't do much for me. Removing the rail would have been better so we can see the Full Monty. On another point I get why people are obsessed with pinned gas blocks (especially when it was an FSB), but sometimes it's more prudent to replace the barrel or replace the FSB with a properly installed low profile gas block.

Originally Posted by Androctonus

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.Attachment 56755

**Androctonus** · 04-07-19, 18:12

Thanks guys. I took the upper to another gunsmith who shaved away the remainder of the A frame and cold blued it again. It's got about as much clearance as is possible now. I would've posted a picture with the handguard off, but I don't really have the tools and know how to do it. I thought about replacing the barrel with a Daniel Defense with a pinned low pro gas block, but I got a good deal on a whole DD upper instead. I've got a spare lower, so I'll have three ARs now. I should be pretty well equipped.

**AndyLate** · 04-07-19, 21:36

Is there a suggested amount of clearance between a rail (and rail mounted accessories) and the gas block?

I only have 2 free float rails, both are ALG. One is 13.5" and pretty rigid, the other is 15" and has enough deflection that I could get the screws for a MLOK bipod mount to contact the gas block. I just moved the mount enough that I couldn't force contact with reasonable pressure and drove on.

**Androctonus** · 04-07-19, 23:43

Originally Posted by AndyLate

Is there a suggested amount of clearance between a rail (and rail mounted accessories) and the gas block?

I only have 2 free float rails, both are ALG. One is 13.5" and pretty rigid, the other is 15" and has enough deflection that I could get the screws for a MLOK bipod mount to contact the gas block. I just moved the mount enough that I couldn't force contact with reasonable pressure and drove on.

Good call moving the bipod mount. I've read 1/16th of an inch clearance between the gas block and handguard is the accepted standard if there is one. But, I've read the minimum varies depending on barrel profile. I know my PWS upper has much less than 1/16th clearance all around the gas block, but it has a medium weight barrel profile.