Well, I guess I'll offer my progressions to a handspring 1/1 twist.
First, on a resi/porta pit...
1. Run and punch to handstand and fall to back, drop 1 arm and roll to belly
(Be sure to drop the arm opposite of the side that you're twisting towards
since you are twisting forward)
2. Run, punch to handstand, block, drop the arm, and try to twist to belly
3. Do #2 and then immediately roll to your back to complete the 1/1 twist
4. Run, punch to handstand, block, and complete the 1/1 twist
Simultaneously, on trampoline...
1. Perform back drop to stand (Be sure that you can do a good back drop)
2. Back drop to stand, drop 1 arm, jump 1/2 turn in forward twist direction
3. Back drop to immediate 1/2 turn and land
4. Back drop w/ 1/2 turn to land and then immediate jump 1/2 turn
5. Back drop to 1/1 twist and land
On a wedge mat into loose foam or resi pit...
1. Handspring - clap hands
2. Handspring - Land - Drop Arm - Jump 1/2
3. Handspring - 1/2 turn
4. Handspring - 1/2 - Land - Immediate jump 1/2
5. Handspring - 1/1 Twist
To the vault...
1. Handspring - Handstand Hop (Hands) Up To Mat Stack - Fall - Drop 1 Arm
and Roll To Belly - (Exactly Like The First Progression On The Resi Pit)
2. Handspring to Immediate 1/2 turn to belly on mat stack & roll to back
3. Handspring 1/1 up onto Mat Stack
4. Take out the mat stack....Handspring clap, land, jump 1/2
5. Handspring 1/2, jump 1/2
6. Handspring 1/1
Some of this stuff I'm working simultaneously. So, it seems like a lot of progressions, but many of these drills can be worked at the same time during a different vault circuit.
For example, I'll usually be working on each training apparatus (porta pit, trampoline, wedge/incline mat, and vault) simultaneously following the progressions in sequence at each training station depending upon where the gymnast is at.
This vault is pretty easy to develop if the gymnast is motivated to do it. Although it doesn't have the start value of a Tsuk or Yurchenko, it's a nice vault in my opinion even though the judges are too dumb to reward it when it's clearly done better than some Tsuks or Yurchenkos.
Anyway, hope these progressions help. Good Luck!