What a huge tick off the bucket list. Firing an RPG, Grenade Launcher and throwing around some grenades is an amazing experience which I highly recommend to everyone!
You must contact Poh direct! I actually tried booking the same kind of experience through my hostel whilst in Phnom Penh and ended up in a very scary and disastrous situation which ended in nothing but wasting an entire day and not shooting anything. The next day I contacted this Cambodia firing range and received awesome customer service from Poh and an experience i'll never forget.. Very grateful for finally making a dream come true!
A couple of things to note is that the site to shoot the big weapons is quite far away so expect a big drive. Obviously you need cash. The targets cost extra (like it shows on the website) but you need a target to shoot at and explode otherwise what's the point! I did 3 oil drums filled with petrol and I highly recommend that! ....just don't miss!