Quote Originally Posted by Trueplaya
If your shadowboxing while holding weights it won't help your speed or power.Reason being a boxer doesn't punch while holding a weight, you end up working your muscles in a different way.Matter of fact subliminally you are holding back speed because if you shot your hand out like a punch should be thrown you won't be able to hold on to the weight.Your holding something back off the punch to keep the weight in your hand.Try weighted gloves or shadowbox with your handwraps on, now you can throw those crazy combos that you'll need in the ring.Put down the weights.
weighted glove/light hand weight

which is why we use light weights as Memphis has mentioned.

Examples of drills you may consider.
either do sets slow eg. 30 jabs, so you feel the muscles OR 10 jabs as quick as you can-think speed OR jab as quick as you can for 30 secs forget technique just keep going as fast as you can.