Shaved FSB Question

AR/M4 AR Technical Discussion
1

So, I’m doing a shaved front sight base, which I’ve done once before. The one I did isn’t pretty, but it works great. The question I have is, is there any reason not to just cut the front half off and go with just one pinned ring? Obviously most pinned aftermarket gas blocks only use one pin and I get that I have to make sure to not expose the gas channel. This is going to be totally covered by a rail so it would be nice to basically be able to cut my grinding work in half and be able to just chop that front portion off. Thoughts?

Finally, if this isn’t a stupid idea, about how far do I have until I accidentally turn this into a useless hunk of steel?

2

But why would you do that or what advantage would you gain? Also keep in mind the gas tube extends well into the FSB up and over the front ring where its secured by pin.

3

The bore for the gas tube extends approximately half way into the base, so that portion will extend forward of the ring.

It seems like more work to remove the front ring than to just leave it, especially if you grind it with the FSB in place on the barrel.

4

I already removed it since I had to do that anyway and I find that to be pretty easy to do. In fact, I’ve already cut the sight triangle off. The main advantage is that it will basically cut the time I have to spend shaping the gas block to fit under the rail in half since I would only have one side to do. The last time I did this, the thing that took forever was shaping the area above the rings that go around the barrel. I could swear I saw pictures of it done like this one time but I’m having a hell of a time finding them now. As a secondary, and much more minor advantage in this case, it would also save some weight.

5

Now that you have it off why not put a low pro block and be done with it?? Seems like a lot to go through to save $35.

6
  1. No chance of misalignment.
  2. $35 is $35 plus the cost of shipping the barrel and labor to have it installed professionally or the cost of the jig to make damn sure I don’t misalign it.
  3. While the consensus is that a pinned gas block is not absolutely necessary for this application, there’s no disadvantage to having one.
  4. I personally find it a lot easier to tap out a taper pin or two then to mess with having to heat up and muscle out and risk stripping a set screw that has red loctite all over it.
7

You don’t use red loctite. My Geissele block specified blue, if any, for the set screws.

There are also blocks available that are easily user pinnable with a drill press like the Geissele block I mentioned a or the 87 Industries unit. ALG Defense carries a less expensive steel version of the stainless Geissele block.

http://87ind.com/products/pinblock

http://algdefense.com/accessories/low-profile-gas-blocks.html

8

I don’t have a drill press. I do have a Dremel, and a FSB and all the skills needed to turn it into an excellent low profile gas block. Oh, and a question about whether there is any down side to cutting off the front ring and just leaving a nub there. :cool:

In all seriousness though, that’s interesting about the Geissele gas block. Both Grant and IG have strongly advocated using red with gas blocks because of the heat. I love his products but I think Bill Geissele may have some type of issue with loctite. I have an MK2 rail and it says to use purple, if anything, on the screws for the rail pieces. I tried running one with none and sure enough the rail section holding my vertical foregrip shot loose. Used some blue and it was good to go. Decided I didn’t want it on there after all and it came off just fine.

9

Nothing wrong with shaving your FSB instead of replacing it with a low pro gas block.

Here’s the link to the thread about cutting an FSB to a minimum
https://www.m4carbine.net/showthread.php?74711-Shaved-and-Cut-in-Half-FSB

10

Put the Dremel down and back away slowly… :slight_smile:
This can be done with a Dremel, but it doesn’t come out very clean or even. If you don’t mind paying for the cost to mail it (and trusting me), I can shave it for you for free. I have a band saw and couple high end knife making belt grinders that make it a quick and clean job. I can shave it any way you want it. I’ve done a couple shave jobs, and cleaned up one that was done with a Dremel.

There is no issue with removing Red Loctited set screws as long as you have a bottle of un-cure on hand (costs about $6 delivered). Bill G may be leaning to the side of ease of removal in recommending Blue for set screws. I assume the reason he recommends purple is because although it is “low-strength,” it is designed for fine thread/small screw applications and will lessen the chances of a user damaging anything and returning a rail. Purple is stringer than people give credit for. Just for fun I loctited a smallish bolt and wing nut to see if I could break them apart by hand. Could not get them apart 24 hours later.

11

Thanks for the link Mistwolf. Elephantrider, I appreciate the offer, but I already cut most of it and I’ve already done one so I’m confident in my ability to do the job to my own satisfaction. Like I mentioned, it will be under a rail so it doesn’t need to be pretty, just has to work. Thanks again though.

12

I’d pay more than $35 to avoid having to grind down an FSB. And the intake on every Lo Pro I’ve seen is pretty big, and hard to misalign.

13

I’m not going to say I have a lot of money or time, but at the moment the bias is toward time. Get this, I actually have done most of the cutting with a hacksaw. :0 Truthfully, it seems to be coming out quite a bit nicer that way. Still haven’t decided if I’m going to chop the front off or not, but at the moment I’m leaning toward not. I’m thinking that second taper pin can’t hurt and that nub, even though it will be hidden, is super weird looking. I may change my mind once I start shaping that side knowing full well that I could probably get away with just cutting it off, but that’s where I’m at for the moment.