Drop services use highly optimized applications, tuned to the byte code level. They poll the registry using all of the 5 connections on each registrar they control at the time each domain is scheduled to drop with many, many thousands of domain availability checks, and then when they detect that the domain has been purged from the registry, immediately send a pre-generated EPP command to create the domain for their respective winners.
Drop, Netfleet and DomainWatch all compete at this level, where the battle occurs in the sub millisecond time frames. They spend many thousands of dollars in development at the code level to jockey for that added advantage each day, and it's a continuing effort as they each try to outdo each other.
It's not conceivable that you can hand register faster than these guys with the systems that the other registrars use, even if you managed to hit the URL at exactly the correct microsecond. While the registrar you would be using is technically able to create the domain at the same time as a drop catcher, it is not optimized for drop catching. The delays it has between checking the domain and generating an XML EPP command, then sending it would lose you the domain.
The only way you would catch it is if no drop catcher is trying to catch that particular domain.