Re: Need help identifying markings on a Ketland flintlock pistol
Your pistol is a 'light dragoon' type of ca, 1780s but made probably for a trading company or to outfit an expedition. It is not a military piece in the sense of English gov't issue but a copy of the typical light dragoon pistol of the period. They were made by various contractors and, while very similar, are seen with variations in ramrod pipe dimensions & placement. The treatment of the shape of the wood at the muzzle is another variable. Some with a belt hook. A source of info is Brooker's, British Military Pistols 1603-1888.
I have had a number of Ketland and other pistols of the period and have mused over their markings without ever ID-ing any, considering it a lost cause & useless knowledge, should I learn it. In your case the HYC No 46 might be possible to ID by digigent research, which might also shed light on the Newton mark.
Your gun fortunately seems to have escaped the usual bubba effort to clean or repair it. As a restorer the past 50 years, I see the gun as one I would reclaim. The replaceable frizzen spring, broken main spring repairable as well as wood defects. I don't restore old guns to 'like new' condition, but to workable condition as in when last used.
Value as-is $400 mainly for its parts. Cost to restore $1200-1500 giving a final value near that figure - hardly cost-effective.
Hope that helps.