Just a comment on the caliber choice;
1. The .38 Super is highly prized in Mexico, since .45's were (are) forbidden to everyone in the country except the military.
2. If the Rangers had gone into old Mexico, I was told by several rangers I happen to know, and some did in the line of duty, the reason was availability of ammo if needed. They were usually on speaking terms with some of the officials and could be re-supplied there. And they prevented the Rurales from arresting them for illegal firearm calibers.
3. Please let us know also, if Mr. Rohatch was a Special Ranger with commission or a regular commissioned Ranger. See the Texas Ranger website for the detailed difference.
My additional source is the Texas Ranger Museum in Waco, with various sources.