First you must understand that what are sold as iron mounted "Early Virginia" are pretty much fantasy guns that seem to have been invented in the mid 20th century, not the 18th. Having said that they are very popular and do have that "old timey" look that many like.
Most old rifles carry a nose cap to reinforce a very vulnerable area of the stock. Old rifles have a stock that is almost paper thin (well, maybe several thicknesses of paper) and the RR groove with piercings for the underlugs and pipes. All of this adds up to an area that is parallel to the grain and prone to splitting. The nose cap is fit to prevent this as well as covering an area of end grain that is exposed to all kinds of stuff while the rifle is loaded, fired and cleaned. Incidentally, the nose cap is made to fit the stock. If you buy one of the pre made caps you will have to shape the stock to fit the cap. This might work out, but most probably not. Shaping a fore end to fit most of the caps available today will result in an overly thick stock which is not what the old rifles had. Make your own cap to fit the stock and you will have a better end result.