I've got a 20" Bushmaster A3 which is totally stock.  I want a vertical grip but I do not want to invest in a rail forend.  Is there a way to mount a vertical grip to the stock forarm using the holes that are already there?  Is the forarm sturdy enough?  I do not use my AR for any heavy-duty use, just shooting at the range.

Try this Advanced Armament Rail.

Mike

The YHM version looks better, as it can use mount the Tango Down VFG:
www.bushmaster.com/shopping/bmas/yhm-hdg-rail-rif.asp

I've tried the Advance Armament rail and IMHO it's junk.  Several of my accessories wouldn't fit on it (yet they all fit on my DD 7.0 and my MRF-R just fine...).

How tight (rotationally) are your HGs?  Expect some (hopefully not much) lateral movement when mounting a rail and VFG to std. HGs. Probably not enough to bother you, but be aware there will probably be a little.  

I picked up a rail similar to the ones described above (not sure what the brand was).  It worked well enough to mount a VFG to, but it got to the point where the rotational motion of the handguards while holding the grip was too much for me to handle, and my anal-retentive engineer's heart couldn't stand the big crack that would appear between the handguard halves.  h.gif

I ended up buying a Surefire M73 later on, and it's rock solid.  I'm still keeping the old M-4 guards around though.  You never know when you'll need to put 'em on something in a hurry.