What excactly is the "same plane" aperature with the 40L BUIS (which is an option) and how is it different from the standard aperatue that comes on the ARMS 40L?

Either the small or  large  aperture can be selected without changing the point of impact.

On a non-SP the small aperture raises the POI by 6 inches @ 100  over the big aperture.

Alwaystryin,
Ok, a simple enough answer. But now I wonder what the logic is for buying the standard (non same plane) BUIS is.
I can understand having a standard sight that compensates an inch or two at 100 yards, but not understand why I'd want a sight that holds 6" higher!????

If I understand it right, most folks would desire the "same plane" sights.

When you use the irons at longer ranges the small aperture is used as a BDC.

In my opinion BDC is not so important on a BUIS, and could make you miss @ 100 yds if the wrong aperture is selected.

Yep....I figure it's a lot less complicated to just know where your "same plane" sight will fire and do your own compensating at longer ranges.

Thanks Alwaystrying for the esplainin it to me!

Seems like their ought to be some other folks thanking you too, as their was 130 hits on this thread with nobody offering any input. I'm assuming a lot of them just learned something too! (....unless they are just a lot of perverts that already knew but just enjoy peeping and watching in on a guy named "Alwaystryin" at work.   )  

This answered questions I've had about the ARMS 40L and 40L SP. What, however, is BDC? Thanks.