Give us some more info:
1) rifle style: New England/NY halfstock, Ohio, St. Louis.... there are many forms these come in.
2) Is there an under rib?
I would say that it is a New England halfstock. The overall shape of the buttstock is almost identical to the W.H. Watkins rifle on page 76 of "Gunsmiths and Allied Tradesmen of Georgia" by Elliott and Whiskers.
Yes there is an underrib but no entry pipe. The ramrod will enter directly into the nosecap. This being my first halfstock I didn't allow enough wood to inlet the entry thimble before I got to the routed ramrod channel.
I like the basic shape of the picture of Mr. Berkutas rifle shown in this thread but I am afraid that this is a little too Hawkenesque for my rifle.