Why I do not gets share which hits upper circuit and gets reasonable volume to execute trade

Why I do not gets share which hits upper circuit and gets reasonable volume to execute trade like some 30-50% of the upper circuit volume traded. In such cases I should get share in 1 out of 3 or 4 cases but that too is not happening. Why ? This is happening even in multiple cases, not a single cases. I tries to buy share on listing day generally.

It is simple first come first serve basis. They would have placed buy orders before you. There will be a large amount of automated orders and highly volatile stocks such as the ones that hit UC. You won’t be able to get your order in before they do.

Best way to check is note down volume when you place order and pending orders before yours. Sum should be less than volume at end of day