G'day Sparkie. Sounds like you are doing it right.300mm is a pretty good effort for an early find.
To help with pinpointing,try practicing with a coin at home. check the ground in all metal to make sure that there is no metal in the ground. Place a coin on the ground then go into pinpoint mode with the detector. Waive the coil over the coin till the center ring of the target display is fully lit up. This will tell you that it is somewhere under the inner coil. Listen for the maximum audio response also. ( With the audio, you can often pick a screw cap from a $2 coin because of the smaller size of the $2 coin, it is quieter the the Screw caps. A $1 coin is also a bit quieter than a screw cap, but not buy much. This only works in the top 3 inches, with if you are hunting in lawn, is more often than not.) Once you have the pinpointing display fully light up, slide the coil back toward yourself till you lose the signal. Once you lose the signal, push the coil back till you reacquire the signal again. Now waiving the coil in small movements from side to side, slide the coil back toward yourself till you lose the signal again. By feeling around like this, you will be able to tell that the last point at which the coil lost the signal, will place the coin directly under the 12 o'clock position of the inner coil.
I own the 30, but if you own the 70, the Digger has written a very good post on pinpointing in the prospecting mode. From what I have read, pinpointing in this mode also allows for you to get a good idea of how big a target is before you dig it. It may be in the FAQ FAQ at the top of the page, or if you go to page 53 and 54 of this forum, you will find it there as well.
Mick Evans.