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View Full Version : FSB tightness on a new barrel


ABNAK
08-31-13, 16:28
Bought a brand new M16A1 barrel (1:7 twist, chrome lined) that is undrilled for a FSB. I ordered a .625" FSB from BCM and got it today. Sending the whole thing off to Adco for taper pin drilling.

How tight is the FSB supposed to be when putting it on the barrel? The combo I have will turn freely; does not take a mallet to tap it into place. Miked them both and the barrel is ~ .624" and the FSB is .625". Is this going to create a gas seal problem?

Conversely, will a proper taper pin job "pull" the FSB down onto the barrel for a better seal? Is there any way to shim it? I'll assume Adco will know what to do (?).

ETA---by "turn freely" I mean the FSB will turn rather easily on the barrel by it's own weight. However, there is no discernable "wiggle" back and forth (i.e. front to rear).
86 slo-vo
08-31-13, 17:46
Sounds about perfect. Don't over think it.

With the pins in it should seal fine.
Iraqgunz
09-01-13, 00:01
ADCO knows how to do this. Send it off and just make sure that they are clear on your instructions.
Mall_Ninja
09-01-13, 01:24
Conversely, will a proper taper pin job "pull" the FSB down onto the barrel for a better seal?

Heck yeah...


Is there any way to shim it?

Not really, but there is an old school "fix". But dont bother...


I'll assume Adco will know what to do (?).

Heck yeah...
ABNAK
09-01-13, 06:56
Good to hear guys! I figured Adco could deal with it but there's a wealth of knowledge here so I thought I'd ask since nothing's moving until Tuesday anyway.
gman556
09-07-13, 10:24
Good to hear guys! I figured Adco could deal with it but there's a wealth of knowledge here so I thought I'd ask since nothing's moving until Tuesday anyway.

Getting ready to send one of mine into adco myself, because of all the positive reviews I have heard over the years.
ABNAK
09-07-13, 14:54
Getting ready to send one of mine into adco myself, because of all the positive reviews I have heard over the years.

Sent it last week, was supposed to get there this past Thursday. Hopefully I will have it back sometime next week.
Eric D.
09-07-13, 17:49
I had them do one early this year and it turned out great. The only thing I didn't care for were the taper pins they used - They were flush on both sides of the fsb, not long enough. I replaced them with Bravo Company pins without issue. I was even able to hand ream the holes to that perfect 'even on both sides' depth :D


Getting ready to send one of mine into adco myself, because of all the positive reviews I have heard over the years.