I have no firsthand experience. However, from what I have read, the Whitworth were used in the American Civil war (CSA side) and a few other wars as sharpshooter rifles. They are muzzle loaders that have a hex cut barrel, and are very rare and expensive.
I have seen my share of US civil war rifles/calibers (my father in law has dozens) and have yet to see one. But maybe there are more left in other regions that saw its use.
Yes, I've seen one shot at Bisley some years ago. It was a pretty accurate beast at 300yrds. I think there are some good clips on youtube of them being used. Considering Whitworths engineering legacy, it wasn't the easiest of barrels to construct but I guess it did pave the way forward in many areas.
I have shot one a fair bit. .45 cal, very fast rate of twist, you can actually feel the rifle twist in your hands. Accuracy is fantastic at long range. Powder can be hard to find (FG). Pedersoli makes an excellent replica of this rifle.
I hadn't thought about the twist but you're absolutely right - I bet you can feel it move! If memory serves it was a massive reduction on the convention of the day being about 1/20" as opposed to something like a 1/80". I love to fire one of these.
I have actually thought of buying one of the pedersoli rifles. They are an excellent replica. You would likely need to cast your own bullets but that is not a big deal. You should seriously consider buying one. I know that they are available in the UK.
The rifle's accuracy is only limited by the issue sights. I have made a mount held by the lock screws for using a Williams 5D elevator/peep sight. The 36" barrels provide a long sight radius when using the peep. My screen name (457121) is the Lyman mold number for what they call their PH Whitworth bullet mold.
If you are familiar with the trajectory that's perfectly doable. Any bullet 450gr. and up will crush deer at that range. Muzzle velocity is around 1400 fps and at 300 yards will be right at 1000 fps. Hex bullets are not needed but are neat accessories. Cylindrical bullets will bump up and make hex holes in targets.
Greetings all! I've been a hunter for 50 years, but only now planning a trip to Africa. I was fortunate and successfully bid on a couple hunts for plains game in SA later this year and next. Also a rare Native Texas (5th generation) and USMC Vet. Hunt safe y'all!