Clamp on A2 front post differences / question

[HRnightmare]

I recently decided I wanted to build a standard GI style AR with an A2 fixed butt stock and carry handle, A2 front post. I have no need but only an ADHD desire so I ordered a clamp on carry handle, aBarska Optics AW11746 Standard Carry Handle.

I neglected to remember that the barrel is not going to come with the cutouts to install and pin on the front sight. So I am now considering a clamp on A2 or having a gunsmith install the A2 post to the barrel.

The Barska mentions NOTHING about being F height but many of the clamp on's do. I know the difference is minimal but can I assume that the barska is NOT F height?

Thanks.

 

[M1key]

Barska carry handle should be correct height. Armalite makes a clamp-on front sight that is the right height for the rear.

http://www.riflegear.com/p-927-armalite-a2-front-sight-clamp-on-w-screws.aspx




M

 

[HRnightmare]

Thanks. So the Barska is or is not F height?

They said its 1.5"

 

[rbernie]

There is no such thing as an F height carry handle. The carry handle optics mimic the sights of the A1/A2, period.

The F marked front sight base (FSB) compensates for the fact that when Colt cut the M16 barrel down from 20" to 14.5" to make the M4, shortening the barrel made the original front sight base too low. So Colt made a taller FSB, and marked it with an F.

So - 20" ARs get a regular FSB and 16" ARs get an F marked FSB. Both use the same height rear sight.

 

[dogmush]

More correctly:

Carbine length gas systems get "F" marked FSB

Rifle length gas systems get regular FSB

Mid-length gas systems get.......uh, put optics on that thing.

 

[sawcut]

The clamp on front sight base will work fine on a 16" or 20" barrel. It is not "F-marked". F-marked which means the sight (the flat deck, actually) is slightly (around .040) taller than a standard A2 front sight base. Unfortunately, there are no clamp on F front sight bases, but the small difference in height can be made up by raising the front post a turn or two. On the Armalite, the adjacent "ears" are also correspondingly shorter as well.

I have just this set up on both a 16" and 20" AR and it works fine. When the front sight post is raised 2 turns on the Armalite clamp-on sight, to make up for the lack of F height, the top of the post is just slightly (around 1/32") higher than the adjacent protective ears. I don't find this to be an issue. The front sight deck on the Armalite

Instead of turning the sight post out, you can install a taller front post also, accomplishing the same thing.

Some of the information posted above needs clarification. The F front sight should be used on any AR with a detachable handle. For what ever reason, the rear sight aperture on the detachable handle is .040 higher than a fixed carry handle AR, so it needs a correspondingly taller front sight, hence the F sight.

Sorry for the long reply, I looked into the same issue some time ago, and what am I writing is based on obtaining the sights myself and measuring/installing them. The clamp on sight from Armalite is still the best option for putting fixed irons on a home build, in my view, though it would be better if it came as an F height.

 

[rbernie]

Mid-length gas systems get.......uh, put optics on that thing.

Every middie that I've bought with a pinned FSB was F marked, whether it needed it or not.

For what ever reason, the rear sight aperture on the detachable handle is .040 higher than a fixed carry handle AR, so it needs a correspondingly taller front sight, hence the F sight.

I did not know that, and I'm not sure that to be a universal thing but I'm willing to accept it. I don't recall my Colt carry handle having a different aperture from my A2, but it's certainly possible that I missed that fact.

 

[sawcut]

rbernie,

On the rear sight, it is not that the components between the fixed carry handle (A2) and detachable carry handle (M4/A4) are different, it is that when they made the carry handle and rear sight removable, the new sight plane was .040 higher than it was on the A2, so the expedient solution was to bump the height of the front sight post a corresponding amount.

Why this occurred, I don't know, and it only becomes apparent when you start to swap old barrels with A2 front sights onto new flat top uppers. Sight adjustment increments are further complicated with the different gas system lengths and cartridges that can be loaded. But that does not matter much if you just want to zero a rifle once at, say, 100 yards, and just leave the irons at that.

I only got into this myself because I liked the option of having iron sights on the carry handle for some days, and then taking them off and putting on a scope or red dot for a change of pace.

 

[justin22885]

just press on a pin on front sight to where it needs to go, make sure its aligned properly and straight with the rear sight, then drill the pin holes yourself using the front sight block as your drill guide