Howdy Ridge Runner.
I'm 99% sure no rifles were ever designed to blow GI up or anything like that. As I said, these are last-ditch/substitute-standard rifles where production was simplified to the point that they could make them faster and as cheaply as possible. Considering Japan's resources and tactics, making rifles that could intentionally fail just in case a GI picked one up would be a waste of those all-too-valuable resources; by the later half of the war, Japan was reduced to sending military police into houses to forcibly acquire any metal that could be used for their war effort.
Some of those stories come from the rifles at the end of the war allegedly being of such poor quality that they went boom. Or perhaps they were loaded with overpressured handloaded ammunition post-war (or in sporterized/converted rifles) that caused a catastrophic failure. But I think that's all apocryphal or has that one-in-a-thousand grain of truth that gets spread around and becomes well-known "fact". As an example, there's a story that the IJA was reduced to using wooden bullets; the IJA did use wooden or paper bullets in their 7.7mm cartridges but these were for training purposes, function testing, or possibly for rifle grenades and not as battlefield soldier-to-soldier ammunition unless there was a mix-up in the supply lines.
There WERE smoothbore training rifles for schools et cetera that were outwardly looked nearly identical to the Type 38 in every way but were essentially blank-fire-only and not designed to work with live ammunition. Cast-iron or mild steel receivers, undersized (or incomplete) bores, rough fit and finish, and most importantly: Marked for blank-fire-only. I don't think most non-Japanese at the time could read Japanese, especially not your average GI, and quite possibly some of them picked up a training rifle as a souvenir and didn't realize it wasn't actually intended to be shot with live ammo, which could go horribly wrong, I'm sure.
However, the
Type 23 hand grenade (actually a Chinese grenade) could certainly be used to booby-trap a corpse or a crate or a rifle or what-have-you, but in this case the rifle would be used as bait and have a grenade attached to it in such a way that when the GI picked it up, the pin would come out and the grenade would detonate. Swords and Nambu pistols might've also been prime bait for such booby traps, just as knives/daggers and Lugers were prime targets in the European Theater. Type 99 grenades could be used to an extent for booby traps but since they required a rap to a hard surface to prime the mechanism after the pin was pulled, they were mostly used as makeshift mines where a GI could inadvertently step on one and trigger the explosive or as a last-minute suicide bomb for a wounded soldier.
As for serial numbers, here's how they work. The tiny circular marking at the beginning (the photo is upside down, I'm reading it as if it was right-side-up) is a Series marker. Starting around 1933, Japanese production added a symbol to indicate which series/block of (ideally) 99,999 rifles was being produced at a given time, with certain arsenals only producing rifles in that series. For example, Nagoya Arsenal produced rifles in blocks 1 through 12, Kokura only produced blocks 20 through 25, and Toyo Kogyo produced blocks 30 through 35. Production was concurrent between factories, so Kokura might've been making block 25 at the same time Nagoya was making block 12, but Kokura would never have made block 32, if that makes sense.
In this case, I can't quite read the block symbol but I think it's Block 10, as the symbol at the end is the one for Nagoya Arsenal. Serial number is obviously in the 90,000s so more or less towards the end of that block's production. I THINK that would make it late 1943, maybe early 1944. Possibly it's Block 12, making it 1945 (more or less).
Also, like
@baxterb asked, are the Imperial Chrysanthemums still intact on the receiver rings? It's unlikely; most of them were ground off or defaced by the Japanese to avoid insult and dishonor to the Emperor, as the 'mum indicated the rifle (or indeed any weapon with one) was the Emperor's personal property and it would be gross dishonor for it to be stolen or surrendered intact.
~~W.G.455
