You should not being using AutoCAD for this type of stuff. If you want to be doing design, you need to be using a real program. If you do not have access, Alibre is the best bang for the buck. None commercial is around $100 which is very cheap. I use Solidworks and CATIA V5 for design depending on what I am working on. Different programs are easier or better for certain things. If I were you, look into Alibre or Inventor since they are the cheaper alternative. I will list some with difficulty level of learning.
1. Alibre (easy to learn and can do a lot)
2. Inventor (easy to learn and decently powerful)
3. Solidworks (good user interface, powerful for most things except surfacing)
4. CATIA (difficult to use but very powerful)
5. Pro-E (difficult to use but powerful)
6. NX (never used)
Here is part of the AR15 I am working on using blueprints and dial calipers on my AR15.