R.J.Bruce- Yes, they did use drum and nipple. A William Hawken .40 caplock halfstock was for sale on Gunbroker in March 2006 at a starting bid of $5900. It did not sell. There were enough detailed photos of it that I was able to calculate all the dimensions and choose the correct parts. I got a .40 Green River Rifle Works barrel with plug from Gardell Powell, who had worked at GRRW. It was a 13/16" x 36" 1-66 twist barrel, a reject, crooked as a dog's hind leg. Friend Bill used his barrel straightening vise to iron the bends out, and that took some severe bending in several different directions. He got it straight and it stayed that way and shot accurately. I hand-sawed a piece of Vernal (where I live) walnut for the stock and made a very close copy of the original. Overall length was 51 inches, trigger reach was 12 3/4", with about 3/4" cast off (that's what my notes say, but that seems like a lot!) and 3 3/4" drop at the heel I modified a Leman trigger to release at two pounds. It took me 155 hours to build it. I entered it in the Uintah Arts Council Outlaw Trail Festival of the Arts 17th Annual Juried Art Show and won first place in theme sculpture, the theme being "Rusty Rails and Outlaw Trails".
I built a .40 light weight Hawken for Ron, who had shoulder surgery and could no longer handle the heavy .54 Hawken I'd built for him. It is on the right. Don't have my notes to hand, but I probably used Track's Hawken 15/16" plug and tang, #Plug-LR-15-5. I think that was a 7/8" Rice barrel, and I filed the plug and tang down to match the barrel.
On the bottom. My .54 Bridger copy at top, then two .54 Kit Carson copies, then my .58 flintlock and the .40 Hawken. It is like a regular Hawken from the lock on back.
Mtn Meek- If you have a 15/16" plug and tang and a 7/8" (14/16") barrel, you need file only 1/32" off each flat.