I found a very scant amount of reference online, but it appears very similar to the doglocks used on the 1716 muskets. However, they apparently hung in there with just some minor changes until the 1790s sometime, and I don't know enough nor can I find enough dealing with the slight changes to determine if this specific lock is 1716, or maybe earlier and a forerunner, or 1730s, 1750s, 1770s etc.
I think I'm just going to go with 1716, as it'll suit the gun timeline better i.e. a 1720s-30s American recycled piece!