There are a number of cut down methods availble : Hot Wire/Resistor, Pyro and Magnetic.

Pros :

• Low power use.
• Light.
• Very fast.

Cons :

• Explosive - duh.

The pyro cut down is fairly easy to construct using some acrylic tube of the following dimensions :

External Diameter: 10mm Internal Diameter: 6mm Wall Thickness: 2mm

Other items you need are some Estes D-ES2301 rocket motor igniters, transparent epoxy resin, smokeless powder. Rob Harrison has prepared a series of pictures here : Construction of Pyros

Pros :

• Safe.

Cons :

• Can be slow.
• Can use alot of power.
• Can be mechanically fragile.

Pros :

• Safe.
• Fast

Cons :

• Can use alot of power ?
• Heavier than pyro/hot wire ?

Magnetic cutdown