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View Full Version : FSB removal and re-installation: FSB alignment...


websniper
03-18-17, 13:21
So, I removed my FSB from a factory med-length upper after making a few marks with a pencil to get everything lined back up after replacing the handguard cap with a round unit to accommodate a Magpul SL handguard.

After some handling and removing the FSB and trianglular cap, my marks are pretty much obliterated. My question is: Will reinstalling the taper pins pretty much automatically align the FSB to its original position due to the nature of the tapered pin arrangement or is that not necessarily the case?

I found a number of videos on YT about removing taper pins and even reinstalling them, but none really seemed to mention realigning the FSB/gas block...
officerX
03-18-17, 13:28
I'm not an expert by any means but I'm pretty sure the taper pins will get everything lined back up properly.
556BlackRifle
03-18-17, 14:18
I'm not an expert by any means but I'm pretty sure the taper pins will get everything lined back up properly.

I've done a bunch and that is exactly correct. Just align it and put the pins in the correct orientation, slip them both in gently aligning as you go, tap them firmly into place and your done.

ETA: I wipe the pins with a little light oil to help them slip into place.
GH41
03-18-17, 15:22
Like the guys said. I'll add... You couldn't get it wrong if you wanted to.
websniper
03-18-17, 15:29
Roger that. Deed is done. Liking the Magpul SL handguard so far though. Will try to get her out to the range this weekend to verify zero.
officerX
03-18-17, 15:40
Roger that. Deed is done. Liking the Magpul SL handguard so far though. Will try to get her out to the range this weekend to verify zero.

I had to do it for the same reason.
Junkie
03-18-17, 21:54
Roger that. Deed is done. Liking the Magpul SL handguard so far though. Will try to get her out to the range this weekend to verify zero.I just wish they had a rifle length option
websniper
03-19-17, 13:12
Zero has shifted about 2.5". Guess it didn't go back on exactly the same way.... Is this common? It's not a lot, so I'm thinking it's not worthwhile pulling it off again. Guess I should just re-zero...


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MistWolf
03-19-17, 14:08
Always verify zero after disassembly/reassembly
bamashooter
03-19-17, 15:29
Zero has shifted about 2.5". Guess it didn't go back on exactly the same way.... Is this common? It's not a lot, so I'm thinking it's not worthwhile pulling it off again. Guess I should just re-zero...


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Are you saying due to the fsb and not the replacement handguard?
websniper
03-19-17, 16:15
Are you saying due to the fsb and not the replacement handguard?

Well, yeah. The drop-in handguard wouldn't affect the front site base.

The gun functioned fine, so I just re-zeroed and carried on. I'm super anal retentive about these things so it still bothers be a bit, but unless someone has a valid reason, I was thinking 2.5" change in windage isn't enough reason to justify pulling the pins and adjusting the FSB. It doesn't appear visibly crooked or anything...
georgeib
03-19-17, 19:05
Well, yeah. The drop-in handguard wouldn't affect the front site base.

The gun functioned fine, so I just re-zeroed and carried on. I'm super anal retentive about these things so it still bothers be a bit, but unless someone has a valid reason, I was thinking 2.5" change in windage isn't enough reason to justify pulling the pins and adjusting the FSB. It doesn't appear visibly crooked or anything...

Not sure if you have considered this, but your POI shift may be due to the new handguards. They could be torquing the barrel by putting pressure on the new retainer, or conversely the old handguards could have been. Just a thought.
MegademiC
03-19-17, 21:41
Just shoot it. There are so many variables I can't imagine e how it WOULD retain zero. Sights are adjustable for a reason.
Iraqgunz
03-20-17, 05:28
Banging on pins, attached to an FSB and barrel with a punch and hammer have a way of doing this. As someone else mentioned, you should be conducting a new zero anyways.
websniper
03-20-17, 08:07
Not sure if you have considered this, but your POI shift may be due to the new handguards. They could be torquing the barrel by putting pressure on the new retainer, or conversely the old handguards could have been. Just a thought.

I had not considered this but suppose it is possible. Either way, re-zeroed and moved on. Thanks all.
RadScorpius
03-20-17, 17:24
Like the guys said. I'll add... You couldn't get it wrong if you wanted to.

Rare, but it can happen.

http://i69.photobucket.com/albums/i59/hoevito/20151220_093604_zpsww0xmz72.jpg
556BlackRifle
03-20-17, 19:51
Rare, but it can happen.

http://i69.photobucket.com/albums/i59/hoevito/20151220_093604_zpsww0xmz72.jpg

Sorry but I have to ask; is that a PSA?
websniper
03-20-17, 20:20
I have a factory CMMG 9mm upper that is probably that crooked. I can just barely, and I mean barely get it zeroed with an MBUS rear. It's bad. I would send it to them, but it's it's getting yanked for a 5" TROS someday.... It also doesn't actually affect cycling either since it's a 9mm w/ no gas system and it's just nplinker anyway.


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MegademiC
03-20-17, 20:56
Drilling the wholes wrong or screwing up the install is not the same as what the op was doing. The holes will line it up if everything was in spec.


Rare, but it can happen.

http://i69.photobucket.com/albums/i59/hoevito/20151220_093604_zpsww0xmz72.jpg


Story on this?
556BlackRifle
03-20-17, 21:09
Drilling the wholes wrong or screwing up the install is not the same as what the op was doing. The holes will line it up if everything was in spec.




Story on this?

Yes and yes. Inquiring minds want to know.....
RadScorpius
03-20-17, 21:16
Sorry but I have to ask; is that a PSA?

Yep. It is a PSA.
Kain
03-20-17, 21:24
Yep. It is a PSA.

You know, it is things like this that stop me from buying one of their uppers, even if it is going on a beater/range only rifle with an abomination of a lower. I mean, the only one worse than that was an AK I had. Front sight so canted that with windage maxed it shot two feet to the right at 25 yards, no exaggeration. And, yes, it was a century.
556BlackRifle
03-20-17, 21:28
Yep. It is a PSA.

Thanks for the reply. Hopefully they made it right. They had a run of those a while back with several from that run canted like yours.
MistWolf
03-21-17, 00:16
http://i69.photobucket.com/albums/i59/hoevito/20151220_093604_zpsww0xmz72.jpg

A visit from Dr. Sawzall will fix that right up
sig1473
03-21-17, 00:21
Sorry but I have to ask; is that a PSA?

The pic was from this thread:https://www.m4carbine.net/showthread.php?179145-You-can-lead-a-horse-to-water-but-he-still-won-t-buy-a-6920&highlight=you+can+lead+a+horse+to+water
556BlackRifle
03-21-17, 01:18
The pic was from this thread:https://www.m4carbine.net/showthread.php?179145-You-can-lead-a-horse-to-water-but-he-still-won-t-buy-a-6920&highlight=you+can+lead+a+horse+to+water

Thanks!
RadScorpius
03-21-17, 01:28
Thanks for the reply. Hopefully they made it right. They had a run of those a while back with several from that run canted like yours.

Oh that's not mine, just something I found.
markm
03-21-17, 16:11
Wow! That's atrocious!
MegademiC
03-21-17, 19:56
Wow! That's atrocious!

You think someone is going to take a hit from that and say " pff, your fsb is canted.. brah!" I don't think so.



:rolleyes:
That's what just as good as looks like.
markm
03-21-17, 20:04
No one is hitting anything with that mess. :lol:
slimedog
03-22-17, 15:43
Related question - how consistent are the dimensions of FSBs? For example, if the original poster wanted to go back to a FSB, could he just install a new one with the same taper pins in the same holes and expect the gas port to still line up? I would expect that the answer is yes, at least with a spec FSB...
slimedog
03-22-17, 15:54
I just read that the taper pin holes are drilled in a jig with the FSB on the barrel. So, I imagine the answer is no unless you drill a new FSB in the same jig. Sorry for the noise.
tehpwnag3
03-22-17, 15:57
Yes, but it's not ideal. ADCO can do the work and maybe a few other places, but I think it's cost prohibitive to scrap the original and have a brand new one installed down the road.



Related question - how consistent are the dimensions of FSBs? For example, if the original poster wanted to go back to a FSB, could he just install a new one with the same taper pins in the same holes and expect the gas port to still line up? I would expect that the answer is yes, at least with a spec FSB...
tehpwnag3
03-22-17, 15:58
Yes, the FSB and barrel are drilled together as an assembly.


I just read that the taper pin holes are drilled in a jig with the FSB on the barrel. So, I imagine the answer is no unless you drill a new FSB in the same jig. Sorry for the noise.