20" AR and A2 sights just won't work for me

JelloStorm

Gunny Sergeant
Full Member
Minuteman
Feb 23, 2010
1,409
2
42
Northeast Pennsylvania
So I took out an old (2009 ish) Stag Arms 20" A3 with 6/3 removable carry handle today with XM855 and I just couldn't get a zero at 50 yards to translate to that 3-4" the 556 is known for. *Now me being a complete fucking idiot about these sights is not out of the question*

I'm trying to zero the irons at 50 yards. My range only has stationary 25,50,100 and 200 yard targets really. I've watched a few videos that say you take the A3 carry handle 6/3 dial and unscrew it and rotate it 4 positions so it bottoms out -4 from 6/3. Some articles I read say 8 positions, what the fuck.. Almost bottoming out the A2 rear sight, regardless of what the dial says, should be set for shorter range zero. Now my front sight post is up pretty high, almost level with the guards on the sides.

I was able to zero at 50 yards with the small peep where bullet impacts just on top of the front iron. But then moving out to 100 yards, I'm 8" high. Figuring the 0-200 peep is what, 2 moa lower than the smaller peep?, I switch to that and now I'm hitting a few inches lower than center of target. Is my carry handle just fucked or something??

It is worth noting, this is an older Stag Arms rifle and when they originally sent it to me, they neglected to put an F-spaced FSB on it so I could never get the shots low enough. They fixed it and sent it back but it's just sat in the safe forever so I decided to dust it off..

If you bottom out the rear sight and zero @ 50yards with the front sight post, it shouldn't matter what the dial position is, you should still be able to zero it or am I completely missing something? I understand that you would raise the rear sight for the military zero but then I'd be pushing my front sight post out past the wings that protect it...

So if you're pushing Winchester XM855 through a 20" what should I try for best say 0-200 zero?
 
Last edited:
Have you tried setting everything back to zero and checking POI at 25m?

It sounds like you need a taller front sight post. IIRC there was an issue for a while with needing a .040 taller post to get a proper zero
 
  • Like
Reactions: simonp
F-marked FSBs aren’t for 20” rifles. The F-marked FSB is for M4 Carbines because of the shorter sight radius.

With the Colt 723 and 727 Carbines, the FSB was a bit low, so when they tweaked the sights for the M4, they made a taller FSB so you didn’t have to back the front sight post out to get it zeroed.

Standard FSB is lower than an F-marked.

iu
 
  • Like
Reactions: simonp