I guess they made their own bullets with the usual Anderson Machinery.  They made millions of rounds so it would be commercial folly not to have made their own.
 
The packet of Ludlow cartridges I have is from well into the 1860s but the label states that the bullets are .568 calibre rather than the .550 of the Government specification.  This is intresting and cofirms the view that the reduction to .550 was forced by the problems faced in the field.  
 
.568 was the original intended size and it is clear that in the controlled conditions of Range Firing with clean rifles of good quality the obvious conclusion was that there would be far better results with the closer fit.
 
All of who have been Enfield shooters over the years would agree with that.