So, help me get this straight...

There are three versions of the ARMS #40 BUIS:

ARMS #40 - 250-300m large aperature, 500-600m small aperature with a horizon line, and scalloped/knurled windage knob. Fold down height: 0.950"

ARMS #40A2 - with the standard A2 aperatures and standard A2 windage knob.  Fold down height:  1.050"

ARMS #40L - 0-200m large aperature, 300m small aperature.  Fold down height:  0.600"

Bushmaster sells the first one and recommends using a front sight that is 0.040" higher for proper elevation.

Do the other two require the higher front sight post also???

Your milage may vary.

Try the stock Bushy F.Sight before you run out and buy the taller FS. I did'nt need a taller FS for my ARMS #40 and M4 Bushy. If their is excessive elvevation on the FS post then grab another.

Bushmaster use a rifle (low ht.) front sight housing, so it is too low for carbine length barrels. The Colt and some others use the correct mil spec ht, front sight housing that is higher than rifles due to the trigonometry of short barrel vs. long barrels. Hence they sell a front sight post to make up for not meeting the mil spec on their front sight housing. Colt mark theirs for the military armorers to keep seperate, but I forget what the marks are at this moment.
Jack

For a folder the PRI seems to be the favoite and best for SOP MOD NEEDS>
Good shootin, Jack

Stamped letter "F".  But I like the one that says "PRI" better!