I lucked into a great deal on a Bushmaster A2S, but due to eyesight problems, I'm unable to effectively use the iron sights.

I've tried to search and read as much as possible, but it seems like the A2 carry handle models take a third seat (that's further than a backseat) to flat tops.

My purpose is personal/property perimeter defense out to 100yds.

Would you invest the money to swap a perfectly good A2 upper to a flat top upper for more optics options, or just attach something to the A2?

I'm open to informed opinions before I haul off and waste time and money fixing something that, perhaps, isn't broken.

Well my dad has a Colt with carry handle. I zeroed in a 4x Colt scope on top of the handle at 50 yds. It's a bit high at 100 yds and a bit low less than 50 yds.

Yes the flat top is MUCH more versatile, but I suppose it just depends on what you think you'll do with your weapon in the future and whether you think it's worth a new upper receiver.

If you can mount an optic lower to the barrel then there will be less discrepancy when firing at closer or farther ranges than what it is zeroed to. It's not a big deal if you are firing at human size silhouettes … you’ll nail it. You just can’t expect to pick small birds out of trees without compensating.

An A3 upper is pretty inexpensive, but an A2 with a scope on top of the carry handle is still very capable. I'm not a big fan of the goose neck mounts although they do work well, you lose a lot of your field of vision (between the iron sights and the optic body there's a lot of downrange missing from your view).

Great little shooter with the mini ACOG:



A couple of 20 inchers with carry handle ACOGs:

I'm sure optics were an afterthought when building the 1st M-16s but it does work ... not ideal, but they work just fine.

My Colt AR with carry handle Acog is very effective.
My local security team uses Colt 6520's with carry handle Aimpoints.
You will be good with an Acog or Aimpoint mounted on your carry handle.
Mike