Looking at it, several things come to mind.
1: The first thing I see is Grain Runout where it broke.
2: Also it could have been dropped & hit on the lock hammer it could have shoved the lock plate into
the weak area.
3: Too tight a lock fit & barrel movement into the wood/breech area, if it has a drum. Drum could have pushed
back the lock & if no clearance, then stress the wood in that area.
4: Could have had a high spot in the tang of hooked breech & recoil made the wood finally give.
5: It is cracked at the Tang corner, thus possibly 3-4 & barrel movement.
Note. You mention the barrel pins falling out & etc. Sounds to me like you had allot of movement in the barrel
channel & that is a No-No, be it a pinned barrel or a hooked breech with wedge pins. That barrel goes
slamming back with recoil, it WILL break the stock. If it is slamming into the tang screw, it sometimes
cracks the stock dead center behind the tang.
Were it me I would glue the chip back, then Micro-Bed the barrel tang & breech area. Great care on this & use modelers clay to fill all voids & release agent, or the barrel will be in there permanently. Or you may break it
again getting the barrel out.
When you are all done with it, relieve the end of the tang wood fit about .010 & that will give you a little breathing room if you have any barrel movement. Just take a little Kiwi Brown shoe paste & fill the .010 & forget it is there.
When they make stocks for this type of rifle, they take a pile of wood to guy with a pattern copier & tell him
they need maybe 300 like this. No care or concern of the product Quality, just get them made. It only has
to last til warranty is out. If 1 or 2 breaks before the warranty expires, they give out 1-2 stocks & its a cheap
out. Please don't misunderstand me. I am Not cutting the rifle. But it is fact a mass produced rifle has to
get into the selling market Price wise, thus they have to keep the cost down to do so. They can't pick & chose
a $100. piece of wood & build it, sell the rifle for $150-$200 & make a profit. IF that is the market range, I
don't know what the rifle cost, i'm just stating a example.