I’m wondering if anyone here has ever built a dedicated 22LR upper with a fixed fsb barrel and an A2 upper and if so how it zeroed with irons, any experience with the 6/3 or 8/3 sight is appreciated.

I have a CMMG M4 type barrel and an FN A2 rifle upper with 8/3 rifle rear sight, and am thinking of marrying the two.

If it won’t be usable, shots too low or high, then I’ll just throw it on a flattop probably.

Regards!

The F marked FSB is going to be just a smidge higher than a non-F marked.  You can buy a shorter front sight post, or just turn it in a couple more turns, IIRC.

You can always file down a sight post, so I'd expect you could get 'er on.  Would be a nice build I imagine.

With a 50 yard zero I’ve never had an issue zeroing a 22 LR with the fixed tower front sight or fold down front sights.   When I put a 22 conversion in my M-16 A-1 the 22 LR point of impact was not that far off from 0 to 100 yards.   I had to hold over at 100 yards (4”-6”) depending on the 22 LR  but I had to do that with a 50 yards zero with a 22 LR dedicated upper.

A Friend used a Ciener conversion in a Colt 20” 1:9 twist CMV 5.56 with 3-6 carry handle.   He remembered the clicks for different ranges and dialed the A-2 sight.    I don’t think you’ll have any trouble moving the front sight to zero your 22 LR.  I like the 50 yard zero with my AR-22’s.

didn't have a problem zeroing even a short ~10" .22 barrel ... cut down a CMMG 16" barrel and roll pinned a take off front sight base to make a rim fire irons division barrel for my SBR... not an A2 but carry handle... I used a cheap NCSTAR carry handle, so drop the drum sight all the way down, and adjust elevation with the front sight, and use the rear for windage...unfortunately I was not able to track the front sight tower well, and replaced with a railed fore end and added a Striplin flip up fiber optic, still with the carry handle rear

thank you all for the replies, I just got it together.
Now just need to find time to shoot and see how it does. I expect it will be fine now..

Regards