FSB Re-install help

deadman

deadman

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I had a surplus barrel sitting in the drawer and decided today I would install it for something to do.

Knocked out the taper pins and pulled the front sight block so I could install the barrel and gas tube. Went to re-install, and now that the barrel is installed I realized that the fsb has a cant to the right when sighting down the barrel. Any thoughts? I used all the same parts, went back together exactly as it came apart. Any thoughts?

This was a barrel/sight I got a while ago, it wasn't on a rifle when I got it. Its an old pencil barrel marked C MP Chrome Bore, it did show evidence of the taper pins being removed at one point before I had it (and the front pin wasn't set as deep as the others I've had/seen). This tells me maybe the fsb isn't the one originally drilled/installed on the barrel? Any suggestions for how to make it work, or do I call it a loss and go with a different barrel?

Any comments welcome.
 
The barrel extension should be firmly torqued onto the barrel.
Maybe there was misalignment from the very beginning.
 
Yes from the little I've read it seems unlikely the extension spun. I'm kinda leaning more toward my thought of the fsb not being the original and not matching up with the original drilling for the pins.

I'm no expert on this, have read that barrel and sight are drilled at time of install and variation can likely occur. As far as I can tell this makes the most sense for this particular situation.

Go to a clamp on gas block? Not sure what would be available for a .625 barrel.
 
That FSB could have been installed on the barrel and pinned on to be inline with the upper receiver of whatever rifle it used to be attached to.
Now that you've installed it on a different upper receiver, the indexing pin may be in the new upper receiver but the original pinning alignment of the FSB is now off in relation to the new receiver.

That's the only explanation and actually I've had the same experience once when I built my old M16A1 clone years back.
I confirmed it by mounting the barrel into another spare receiver I had and it was not canted off.
 
Travis Bickle said:
That FSB could have been installed on the barrel and pinned on to be inline with the upper receiver of whatever rifle it used to be attached to.
Now that you've installed it on a different upper receiver, the indexing pin may be in the new upper receiver but the original pinning alignment of the FSB is now off in relation to the new receiver.

That's the only explanation and actually I've had the same experience once when I built my old M16A1 clone years back.
I confirmed it by mounting the barrel into another spare receiver I had and it was not canted off.
Click to expand...

Quite possible, I guess this barrel isn't going to work for me. I pulled another barrel from the drawer and tried it, everything indexes well with this one, an old SAK marked unit. Thanks for all the input.
 
Once a barrel has been drilled and taper reamed with a particular FSB, there is very little chance it will work with a different FSB.

Even if they are from the same manufacturer.

I have successfully mounted a pre-drilled FSB on a virgin barrel. But doing mismatched pre-drilled parts is much tougher.
 
deadman said:
Yes from the little I've read it seems unlikely the extension spun. I'm kinda leaning more toward my thought of the fsb not being the original and not matching up with the original drilling for the pins.

I'm no expert on this, have read that barrel and sight are drilled at time of install and variation can likely occur. As far as I can tell this makes the most sense for this particular situation.

Go to a clamp on gas block? Not sure what would be available for a .625 barrel.
Click to expand...

Anyone that makes gas blocks will have one that fits a .625 journal. You're not limited in any way by that.
 
Blastattack said:
Anyone that makes gas blocks will have one that fits a .625 journal. You're not limited in any way by that.
Click to expand...

Well, he's a little limited, they're by no means as common as .750 - and a clamp on like he's asking about is less common again. I bought one from maple Ridge Armoury IIRC.
 
Well the barrel is back in the parts drawer now as I made another one work. As I dont have the proper fixtures/reamers its unlikely I'll do anything with it unless I come across an aftermarket style gas block. I do like the light profile barrels, maybe try and do something else with it eventually.
 
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