The patent date is late, 1836, too late to help the Alamo defenders. But, the guns began showing up in Texas by early the next year, and the Rangers used them as soon as they could get them.
This does not tell you if your revolver will be acceptable to the hosts of such "Pre-1840" events. Call and clear it with them, before taking it along. There are few things that can spoil a good time more than an argument about what is or was historically correct for some time period with all the "know-it-alls"- at Rendezvous, when you didn't think to take your books and research information along to confront these guys. It happened years ago to a good friend of mine, and he took his books and materials with him the next year, and won the argument handily. No apologies, of course, but he was able to use the equipment he brought. And he came in second place in one of the shooting events, to the great consternation of the locals. And, he was only a couple of points behind the first place winner, and both were many points ahead of the third place winner, the prior year's first place winner.