Bottlenecked cartridges
In your picture, so definately not .45-70 either.
Best guess, considering they appear to be fairly long round nosed bullets would be 7mm Mauser (military ammo).
The 7mm Mauser was very popular in Mexico, being the official Spanish military round adopted in 1892, and adopted by Mexico in 1895. Mexico retained the 7mm Mauser as its service rifle riound until 1954, when the adopted the .30-06.
I could be wrong, of course, but 7x57mm Mauser seems like the best bet. I don't remember the exact year, but it was before WW I, so all newer rounds are out of the question. And, it is unlikely (but not impossible) that they would be US rounds, but US rounds would be fairly hard to come by, while 7mm Mauser could be obtained from Mexican Govt supplies. (without their permission, of course, Villa was, after all a revolutionary)
Hope this helps.