>Can someone with good OED access enlighten on the ‘firm’ nature of their research?

okay mav, here is the OED pronouncement in its entirety:

It has been conjectured that point-blank represents a F. *point blanc meaning the white point or white spot on the target, but no such use is found in Fr., or in any Romanic lang. The phrase appears exclusively of English origin and use; and there is no evidence that in Eng. the ‘blank’ or ‘white’ was ever called the point blank. The probability therefore is that blank is here the n. (blank n. 2), and point the vb. (point v.1 12a), referring to the pointing of the arrow or gun at the ‘blank’ or ‘white’; point-blank being a combination of the same class as break-neck, cut-throat, save-all, stop-gap, etc. It may have started as an adj., in point-blank shot, distance, reach, or range, i.e. that in which one points or aims at the blank or white spot.]

the first citation therein is from:
1591 Digges Pantom. 179 The first parte of the violent course of Gunners, commonly termed the peeces pointe blanke reache.