Originally Posted by ThunderCactus
If you're just practicing drill, you don't necessarily need the exact gun, just something that drills the same.
This. You'll want something that functions the same (eg safety, bolt catch/release, magazine release, charging handle), and is the same length. An M16A1 with some parts changes will fulfill the drilling duties of a C7 just fine.
However, the C7 is mostly ambidextrous, so you'll need to install that stuff.
If you've got a KJW, or have a KJW lined up, it'll work just fine as your base. I prefer KJW M4s over WETTIs.
Edit: Just an FYI, if you aren't aware of the difference between the M16 and the C7, take a look at this thread:
There's not much difference, and this thread will help you know what you need to modify to get to a C7. You can use your judgement on whether or not you need to make the actual modification in order to perform your drills.