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6/17/2014 8:35:00 AM EDT
It is easiest to order a new A2 20" Govt profile barrel, but it seems they all have is an F marked FSB, unless you buy the more expensive kit with a bunch of stuff I already have. Is it a major headache to use the F FSB instead of the unmarked FSB, because of the .040 height difference? Seems I could shorten the sight post, or mill down the FSB to match an unmarked FSB. I want to use a A2 upper receiver, and not an A3/M4 upper.
6/17/2014 8:49:43 AM EDT
[#1]
You just might find that you are pretty much OK as is...on a 20" machine.   If I was going that route, I'd shorten the front element, but only if I had to.  Just too bad Colt can't get all their A4s properly marked, with the "F" FSB.  The opposite of your issue !
6/17/2014 9:03:43 AM EDT
[#2]
Seems I hear guys telling of having to screw the sight post down almost as far as it will go in order to zero the weapon. The logical fix would be shorten the post to raise the front of the barrel up.
6/17/2014 1:22:24 PM EDT
[#3]
Both flavors are out there... And on a 20" in most cases the adjustability of the weapon should be able to handle the difference.  Worst case you spend a few bucks and get one of the shortened special front sight posts from brownells. Either way, it shouldnt stop you from getting the barrel you want.
6/18/2014 3:32:46 AM EDT
[#4]
Further mitigate this issue by utilizing and improved battle-sight zero. What this does is elevated the rear sight a bit and allows it to adjust below the 8/3 marking.

With the rear sight elevated 3 clicks off bottoming out, your front sight post wont have to drop down as far into the FSB.

In addition, utilizing this method will give you 100 and 200 yard zeros while still being able to utilize all the markings on the 8/3 drum.

The New Rifleman IBZ Please note, the click values are different for a detachable carry handle and a A2 rifle. A2 drums should be set up to allow minus 3 clicks for 100 and 200 yard zero capability.

6/18/2014 5:08:52 AM EDT
[#5]
Quote History
Quoted:
Further mitigate this issue by utilizing and improved battle-sight zero. What this does is elevated the rear sight a bit and allows it to adjust below the 8/3 marking.

With the rear sight elevated 3 clicks off bottoming out, your front sight post wont have to drop down as far into the FSB.

In addition, utilizing this method will give you 100 and 200 yard zeros while still being able to utilize all the markings on the 8/3 drum.

The New Rifleman IBZ Please note, the click values are different for a detachable carry handle and a A2 rifle. A2 drums should be set up to allow minus 3 clicks for 100 and 200 yard zero capability.

View Quote

Thanks. I have a detachable handle as well, but plan to use the full A2 upper. I think the sight drum on the detachable handle is marked 6/3 and the full upper is 8/3. But- I will use your method. I also decided to order a full barrel kit, which gives me a choice of a plain or an F marked FSB.
6/19/2014 9:15:48 PM EDT
[#6]
I had a factory Colt 6601 with a F-FSB.. didnt have any issue zeroing it
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