I have found that if a stock is up $1 to $2, and moves up immediately after the bell, with a gain of 40 cents, that it will, most of the time, go another 30 to 40 cents higher. These trades move fast, and its usually just a couple a minutes at the most.
Bought Holx, about 3 weeks ago, at 9:31, out at 9:33, for $3.50 per share gain. If I remember correctly, it was up about $1.50, premarket. Went up another 50 cent on open, and I jumped in,
Went to a little over $5 above, my entry price, and dropped back down to $3.50, where I sold.
I have been keeping track of these type stocks for a little over a year, and you can make a profit here, but you must be quick.
I have only been trading about 14 months, and I am by no means expert, on "trading on the bell", but it seems to work about 75% of the time. My main problem is, my lack of knowledge, & getting the trade executed fast.
Joey