The Walls family seemed to have been inhabitants of the Kirby Hill/Kirby on the Moor/Milby area for generations
Richard Walls married Ann Roper (Raper) 7/8/1737, they had 3 children that I can find
Richard 16/8/1738/9 - ? our horn inscriber
Ann bap 1/6/1741
Elizabeth bap 24/3/1742
Ann married John Buttery a yeoman on 10/1/1764 by lic. one of the witnesses was Richard Walls
Elizabeth married Thomas Stubbs a grocer from Ripon 27/12/1758 by lic. with consent of parent
one of the witnesses was Richard Walls jun.
So we now know that the nephew and niece mentioned in the 1800 will of Richard Walls were his sister's children.
I did notice that on the same page as the bap of 'our' Richard Walls s/o Richard there was another Richard s/o William Walls (who appears to sign many entries in the parish registers, so a church warden perhaps)
Looking for a marriage for Richard Walls - Kirby, I found banns.
One set to Jane Barker in 1761 I cannot find the PR entry for the actual marriage although Boyds record it as in 1762 at Kirby Hill.
Another to Mary Kemp in 1765, the marriage 24/11/1765 happened in Aldborough and one of the witnesses was William Walls, suggesting this is the Richard s/o William - no occupation given on the entry.
Although I can find 3 children baptised in Kirby to Richard Walls, none have a mother's name. All are after the 1765 marriage (1769, 1770, 1772)
So possibly the Richard we are looking for had no children, borne out by the will naming his niece and nephew, but where the PR of the marriage is I do not know.
All in all some info on Richard Walls but nothing that conclusively pinpoints him as being the maker of the horns.
An afterthought - if these are powder horns, then it is likely that the owners were military/naval men or land owners/gamekeepers perhaps