There were several 11 mm Remington Rolling Blocks made. Most common is probably the Argentine RB 11mm, but called the .43 Spanish. Egypt had their own 11mm, similiar to the 43 Spanish, but different. Darn if I can remember the third one for sure, perhaps a western European country. The 1871 German rifle (not a RB) had a 11mm too, but called the 43 Mauser. As I recall, none of the 11mm Remington cartridges had the same dimensions.
hiwall's post shows the paper patched bullet for a 11mm to have a .467 diameter. A long time ago I bought some UMC 43 spanish ammo probably made around 1900 and it was not paperpatched, but did have black powder in it. Today, if I order bullets for my .43 Spanish, I buy .439 diameter ones.