Can the small apature be taken out of the 40L just leaving the large one?

I suppose that you could dremmel it off if you wanted to.

I was thinking more of taking the thing apart and just putting it back with the large one.

You may not be able to do that cause I think only one of the aperatures is threaded.  The other just rides on the threads outside or inside the other.  It'll take someone that owns one to tell you this for a fact.  If there is no gap between the two where the connect on the threads, then youll just have to dremel one off.

Yes Yes Yes....you can remove the smaller aperature on the ARMS 40-L without resorting to cutting.

Here it goes:

Use a punch to remove the roll-pin that runs through the adjustment knob. Once this is done, remove knob (CAUTION: There are two detent ball bearings and springs under the knob, don't lose them) and use a flat-blade screwdriver to remove the "axle" that the sight moves on. Once removed, the small aperature can now be separated from the large one. Now, re-insert the "axle" and replace large aperature. Replace adjustment knob and re-install roll-pin.

This should take less than 20 minutes.