Go here to launch A-5 builder and get an approximate idea on how this handguard will fit over the barrel - OPSGEAR® A5 Builder

In the options, pick Lapco 12" and 9" SR Handguard, they are made by Metadyne for Ops Gear so they are the same item. It looks like you will have just barely enough space to put the APEX tip on it, but I am not sure.

I don't think Ops Gear stocks APEX ready Lapco bigshot though.