I've had a look through Skennerton Rifles & Carbines and it looks as if this is a Mk.III Short Rifle type .
The lock is Enfield dated 1864 and the furniture is iron.
Still uncleaned I was looking for ID on the receiver when I realised it was all Snider marked, no ordnance markings at all (yet)
Appears to have a 3 groove barrel of 30.5" ish. The Mk III SR should be 5 groove shouldn't it?
Essentially, is it a commercial put together of the time on a reused stock? or something else?
No pics yet as it's in the caustic bath. Maybe more info tomorrow.
Another question. Would cleaning rods of this period still have one end threaded?
Oh yes, and the mainspring twanged on me nearly taking my finger with it. Can still feel it 5 hours later. Checking on the bust spring I can see it had been more than ¾ cracked through for many decades and just waiting for me to discover such. No mea culpa