Welcome to tnet from Indiana. I don't own the 300 but it takes time to learn the machine. Here are a few tips that might help.
Take an index card or sticky note and write down the most common vdi numbers andkeep it on you when you hunt.
(test the VDI numbers on your machine with the coins on the ground) Take notice of how the vdi changes on these coins/jewelry as you raise your coil from 2,4, 8 inches.
Practice pin-pointing by hiding coins under a sheet of paper or cardboard (maybe have someone else do this for you)
- Practice locating coins without pinpointing by using the x method
- If you don't already have one then plan to get a good pinpointer - Garrett or deteknix
- watch youtube videos on your machine (live digs-help alot) - but don't expect to be digging seated cc dimes anytime soon either.
- read everything twice - including your manual (I've made this mistake on every metal detector I have purchased. Then a year later I feel like an idiot)
- start hunting at the easiest locations - very important you learn your machine and build confidence- tot lots with mulch or sand. Then small strips on softball/baseball fields
(Think if mom just gave me fifty cents what path would I take to the concession stand?)
- Read about the halo effect (this may be what your experiencing) - my tesoro would find the smallest stuff like the back of an earring at 7 inches it can be pretty frustrating at times.
- go slow, learn to sweep properly and level - dig as much as you can live with.
HH