Hi Gav and Colin,
Excellent observations on this extremely unusual object, and I completely agree Gav, it is truly a shame when these intriguing subjects simply fall away without any effort or suggestion toward discovering what they might be.
The reason I bumped this forward was to instigate more discussion, and to note the possibility that has been suggested to me by research done by Anandalal. I had not yet added the subsequent material as I was still compiling notes and should have bumped the thread with notes added
Apparantly in early forms of cannon, there were varying types of projectiles along with, of course, many prototypes of devices to propel these using the then innovative use of gunpowder. According to descriptions of such early forms of 'artillery' in the 1932 work of J.L.Boots ("Korean Arms and Armour"), one such projectile fired from a 'fire tube' was a huge arrow, sometimes nearly 6 feet long. These had a heavy iron point or head of up to between 4 and 5 lbs. Although I'm not sure of the size of this example, it should be noted that in some cases there were numerous arrows fired simultaneously and of course commensurately smaller, which would correspond with Gav's observation as well of insertion into a bamboo shaft.
These appear to have been in use along with many variations in both the type of propulsive weapon detonating the gunpowder, and the type of projectile(s) from about latter 15th and into 16th century in Korea, which seems of course relatively late considering much earlier use in China and Europe of gunpowder in warfare.
As noted, this iron object is provenanced from Sri Lanka, and there does seem the distinct possibility this might be the head component of one of these type of early projectiles. Naturally the question is what type of weapons firing these type 'arrows' might have been used there, and does this correspond to known data such as narratives, artwork or provenanced similar items that might better identify it.
With this perspective giving better view of the direction headed in the search for identification, I hope we can continue with observations and ideas.
All best regards,
Jim