I posted this under 'Slings and Other Access' and didn't get any responses, so I'll try here.
I am putting together a 20" A4gery. Still waiting for some parts so I can't measure the length. While I'm waiting I want to get a soft case for it.
My question is, what size case do I need to get? 40? 42?
I realize that the inside measurement seems to be about 2" less than the outside measurement. I'm thinking I need a 42", but I want to be sure before I order.
Is this right?

C'mon, I know there are those who have 20 inchers and have bought a soft case.
What size did you get?

I went with a 42" case from Midway.  http://www.midwayusa.com/eproductpage.exe/showproduct?saleitemid=816638

I just put together a 20" AR15 with A2 stock and it fits very well into this case.

al - Thanks for the reply, I guess 42" it is then.