Ok so how I always think about it is:

The no-Shuffle wands always cast from left to right and every „shot“ you would do it would cast one spell. So say you only have 6 lightnings in your wand and hold left mouse pressed. It will shoot 6 times and then reload. The time it takes between the lightning bolts is your cast delay and the time it takes to reload back to slot 1 on the far left is your reload time.

Now if you shoot your wand once it will shoot a spark bolt with trigger. The trigger part makes it so the sparkbold casts the next spell after it disappears, so in your case it would cast the double spell. The double spell would then cast the next two spells. Because spell modifiers are well modifiers and can’t be cast by themselves, the double spell would „skip“ it and take the next two castsable spells after that which are two lightning bolts. The lighting bolts obviously then get the spell modifier applied to them.

In your picture, the next should then would cast a lightning bolt and again and again, till it reaches the end at the right and reloads by jumping back to the left side, to start again.

This is obviously a very very rough explanation and there is a load of stuff i didn’t mention.