Iron sights, A2 upper with carbine FSB

[Matt-CZ]

There's an AR-15 I'm interested in buying. It's a bit unusual. It's an A2 upper (non-removable carry handle, 8/3 drum) with a 14.5" sight radius (M4 length gas system on 16" barrel)

Would the 8/3 drum clicks be the same elevation change in MOA on a carbine sight radius as on a rifle sight radius?

Apologies if this is a stupid question. My online searching doesn't seem to bring up many examples of this kind of configuration. Most rifles of this length have removable carry handles 6/3 drums.

 

[mac1911]

Sounds like a barrel swap?
If you do have a Carbine FSB it will be taller than a A2.
Im not sure how much different the 8/3-6/3 rear sight adjustments are although shorter sight radius you get more MOA shift per click.
If you zero it for 5.56 NATO you can see quickly how well the yardage indicators are dialed in by just testing down range.
Being a fixed A2 i would not be surprised at all that manufactures just installed 8/3 on all A2 receivers no matter what barrel configuration they stuffed on it.

 

[Matt-CZ]

Sounds like a barrel swap?
If you do have a Carbine FSB it will be taller than a A2.
Im not sure how much different the 8/3-6/3 rear sight adjustments are although shorter sight radius you get more MOA shift per click.
If you zero it for 5.56 NATO you can see quickly how well the yardage indicators are dialed in by just testing down range.
Being a fixed A2 i would not be surprised at all that manufactures just installed 8/3 on all A2 receivers no matter what barrel configuration they stuffed on it.

I think it's original. It's a pre-94 Eagle Arms rifle.

Not sure why a rifle would be built this way other than what you suggest, just the manufacturer slamming parts together. Probably going to pass on the rifle, it's a good price for a whole pre-ban rifle, but the non-standard irons are a big turn off.

 

[mac1911]

Short answer no.
Carbine front sight base for a detach carry handle is taller than A2 FSB
I dont know for sure but I think the rear sight 2/8 or 3/6 have the same thread pitch making the mechanical adjustmwnt the same but the sight radius changes the movement down range.

A Very Useful M16A2/A4 M4 Dope Chart - The New Rifleman

Looserounds.com shared this chart with me, increadibly useful for bullet drop and windage out of your AR15

www.thenewrifleman.com

This chart maybe helpful

 

[mac1911]

I think it's original. It's a pre-94 Eagle Arms rifle.

Not sure why a rifle would be built this way other than what you suggest, just the manufacturer slamming parts together. Probably going to pass on the rifle, it's a good price for a whole pre-ban rifle, but the non-standard irons are a big turn off.

i would not pass it off just because of the sights.
I would bet if you zeroed correctly your adjustments would deliver hits on target at range.

The "F" marked FSB is taller so you might need a bit more adjustment on the front sight to get zeroed vs a "A2" FSB.

 

[Matt-CZ]

i would not pass it off just because of the sights.
I would bet if you zeroed correctly your adjustments would deliver hits on target at range.

Thanks for the info, you've given me a bit more to think over.

 

[Matt-CZ]

Here's an image of another rifle that is configured similarly from Eagle Arms.

It's the top rifle.

https://www.rockislandauction.com/detail/51/1814/two-eagle-arms-semiautomatic-long-guns

 

[mac1911]

Here's an image of another rifle that is configured similarly from Eagle Arms.

It's the top rifle.

https://www.rockislandauction.com/detail/51/1814/two-eagle-arms-semiautomatic-long-guns

Look at the chart its about a 1/4 moa rough difference with A2 sights rifle vs carbine.

you can get real technical and measure the mechanical move ment of the sight.
Ex
a .005" mechanical change on a 2 0" sight radius is aprox 1" same sights with a 15" radius . 005" mechanical change will be aprox 1.38" down range.
Your error in your hold will be more.

 

[Matt-CZ]

Look at the chart its about a 1/4 moa difference with A2 sights rifle vs carbine

That's not bad at all. Thanks again for the info!

 

[mac1911]

When you get it and zero it its now "your" rifle
Get to know it make some notes and slip it into the butt stock trap.

 

[Matt-CZ]

When you get it and zero it its now "your" rifle
Get to know it make some notes and slip it into the butt stock trap.

I'm trying to replace my large pin colt with a standard milspec lower. I'd either prefer a 20" A2 rifle, or a flat top carbine. This one is not really either, with is a bit annoying. Still mulling over whether to buy it or not, but the info is much appreciated.

 

[mac1911]

I'm trying to replace my large pin colt with a standard milspec lower. I'd either prefer a 20" A2 rifle, or a flat top carbine. This one is not really either, with is a bit annoying. Still mulling over whether to buy it or not, but the info is much appreciated.

Only difference between flat top and the M16A2 carbine is the flat top.
Oh and you get more rear sight adjustment with the fixed A2 rear sight than a carry handle rear sight.

Although stick to what you want .