Thank you for the replies. I am aware of the capture of some of these in the Philippines and did seriously wonder if the kanji were Japanese in origin. I would definitely post this in the Japanese rifles section, or anywhere else that might be more appropriate, if I were certain that the markings were Japanese. I was also, remotely, aware of their use by the Chinese.
I have spoken (prior to posting this thread) with one person directly who is quite good with Japanese, and have indirectly contacted another. The first didn't exactly recognize all of the characters, or the English translation of the their literal romanization. The second, going off of my old, blurry/hazy picture thought they recognized アザートン, romanized as azaaton, which apparently translates to Atherton. There was a
U.S.
destroyer escort during WWII named the U.S.S. Atherton, which did operate in the pacific theater near the end of the war and today, ironically, is in service in the Philippine navy, having previously belonged to the Japanese following WWII.
I'm no expert, but the kanji don't seem to me to match those that were romanized as azaaton, no doubt because of the poor image quality. This may well all be possible, but it seems to be quite a stretch to me that the name of a U.S. destroyer escort is engraved in Japanese on a rear-echelon, infantry rifle, especially since this destroyer doesn't seem to have ever been captured by the Japanese during the war, unless the Japanese retained and fielded some full-length M1917 rifles after the war on naval vessels? It appears that that vessel was acquired by the Japanese in 1955. Additionally, the Japanese obviously renamed her while in their service.