Shaved and Cut in Half FSB

AR/M4 AR Technical Discussion
1

I’ve been meaning to post about this for a long time, but only recently I recovered this pic from a dead hard drive:

I ordered the Centurion Arms 12in rail, and I’m planning to cut down the FSB whenever I get around to installing the rail. I’ve been thinking that if I don’t like the weight, I’ll have the barrel reprofiled. I then remembered I read about cutting the FSB in half for ultimate weight savings.

Since I’m going to be cutting up the FSB anyway, is there any reason NOT to cut it in half like in the pic? I figure that if I do end up having the barrel reprofiled, cutting it in half will allow a little bit more weight to be removed.

2

Wow. Interesting Idea. But I think I’d take the minimal extra weight and the extra taper pin strength.

Eh… but if it’s under the rail… I don’t know. Whatever was the least work I guess.

3

tagged for interest

4

Just from looking at the photo I can see that the upper part that mates with the gas tube has been converted to a moment arm, if I understand the concept correctly. I would be concerned that over time the gas pressure could potentially cause deformation and a subsequent loss of sealing at the gas port in the barrel should the remaining support arm deflect. Just a thought…
Marty

5

In easy to understand terms. Over time the stress of gases may push/bend the single leg and give you gas leakage.:smiley:

6

Yes, what donr said. Thank you for translating!
Marty

7

I did the cut in half FSB with Project Featherweight https://www.m4carbine.net/showthread.php?t=39599&highlight=Project+Featherweight with a RRA stainless barrel. No problems yet in over 3K rounds of Radway Green 62gr ammo. Study group / Sample of 1 but it is data.

8

How did they deal with the exposed cutout for the other taper pin?

9

The barrel was turned to .565" there and covered by the Troy 11" TRX rail. https://www.m4carbine.net/showthread.php?t=39599&highlight=Project+Featherweight

10

I think I first read about the halved FSB in your Project Featherweight thread and then sometime later I stumbled onto the pic in my post.

Would an A1 barrel profile be thin enough to remove the taper pin cutout?