Here is my collection of true touches of Grandsire Doubles of up to 40 changes. These touches are ideal for learning as you can readily write them out all the way through, especially the 39 containing only one bob (putting the third into the hunt for the rest of the touch).

For 20 changes, the shortest possible length, there are 3 callings, 4 touches with rotations. Of these, only one calling (1 touch) uses conventional calls:

20 bb
20 ee
20 sg

Touches of 29 changes are not possible, for 30 changes there are two callings giving us 4 touches with rotations. Of these, only one calling (1 touch), the plain course, uses conventional calls.

30 ppp
30 spe

Now for 39 changes, there are 5 callings/touches (they cannot be called rotated). Of these, only one uses conventional calls.

39 pbpp

39 sepp
39 gpsp
39 egbp
39 ebsp

Finally, for 40 changes, there are 6 callings, 12 touches with rotations. Of these, three callings (5 touches) use conventional calls alone.

40 ssss
40 spsp
40 sbsb

40 gggg
40 gbgb
40 ppge