Jaq, we must have angered the EZboard gods! They move in mysterious ways, mostly without rhyme or reason.
About the detachable foreshafts:
I suggest that the primary purpose of detachable foreshafts has little to do with a reloadable atlatl dart (or throwing or thrusting spear). Instead, I think the forshafted darts were for repair purposes - repair logistics.
Lets ee if I can explain myself...First, a little bit about atlatl darts (you guys probably already know this stuff, but I can only think it through out loud if I include all my thoughs).
Atlatl darts are tempermental creatures. Like arrows matched to a bow, darts must be matched (within reason) to the person throwing them, and to the atlatl itself. Atlatl darts must flex to varying degrees, depending upon the amount of power applied and the general force imparted make the thing move toward a target. The flexibility or "spine" of the dart shaft is therefore an important feature in an atlatl dart.
Darts may be rather finely tuned to the individual using them. Just as a 60lb. longbow requires stiffer arrows than a 30lb. longbow, an atlatl dart thrown by a person with 100lbs of force would require a stiffer dart than a dart thrown with only 50 lbs of force (just picking numbers out of the air).
Photo of dart flex, for fun:
The flexibility or spine of things like arrows and atlatl darts can be adjusted in just a couple of ways. I'll only talk about two ways of spine adjustment 1) length of the shaft, and 2) weight/mass of the point.
Adjusting Spine by Alterning the Length of the Dart Shaft:
All else being equal, a longer shaft will be more flexible than a shorter shaft. When testing a dart's flexibility (aka spine), I take a straight shaft and push it straight down on a bathroom scale, and I take note of the poundage imparted at the moment they begin to flex. I find that darts function best for me if they flex between 5lbs - 7lbs on the bathroom scale test.
When scaling my dart shafts, I will start with an extra long shaft and test on the bathroom scale. If it is spined too light, shortening the shaft will begin to increase the spine. By shortening the shaft, you can dial them in to the specific spine that works best for you.
Obviously, if the dart shaft is too stiff (even at the extra long length), you can only adjust it by making increasing the length somehow (you could also make it weaker and more flexible by scraping or sanding off wood, but for simplicity's sake, let's forget about that for now).
Let's just say that if the dart's way too stif, we'd be wise to discard it and select more appropriate material. Wiser yet to select more appropriate material to begin with. It doesn't take long to develop expertise in picking out near perfect shaft material from the outset.
Adjusting Spine by Altering the Point Weight/Mass:
Assuming that the shaft is just a little too stiff, you can easily adjust the dynamic spine of the shaft by adding more weight/mass to the point end. This can be accomplished easily and effectively by using a foreshaft of denser hardwood, into which your stone or bone point would be set.
If your dart is too flexible, you could either shorten the dart shaft, or lessen the point weight/mass. With a foreshaft, you might simply use a different foreshaft and point assembly, or shorten the foreshaft, etc.
Now imagine you are a paleolithic hunter off on a caribou hunt. Your atlatl darts are one solid shaft - with no foreshaft assembly. Your stone point is lashed securely into the business end of your darts. You throw and miss your target. The point shatters on a rock...or worse yet, the point is forced back into the dart shaft and splits the wood. It's not too bad, you can make a repair, but this repair will be costly in two main ways: 1) It will take time to make the repair...down time from your hunt. Although this in itself is the least of the worries provided you still have extra darts. If not, you might be in a more serious predicament. 2) You're very likely or nearly certain to have to shorten your dart shaft in order to create a new hafting area, and this is going to mess with the spine of your dart and the integrity of your system.
Clearly, if your dart was ideally spined to being with, shortening it will make it less than ideal. At best, you might get a way with shortening your dart several times before it became way too stiff and therefore inaccurate.
Again, any time repairing darts in the field takes away time from the hunt. You can only carry a limited number of darts with you. Back in your main camp or village, you have lots of time for repairs and for making new equipment. But out on the hunt you must be focused on killing, not on arts and crafts.
You've got several dart shafts with you (an equal number as Paleohunter #1) and a bag of pre-prepared foreshaft and point assemblies. All are relatively interchangeable with any of the dart shafts you carry. Maybe you even thought ahead and made a few forshaft/point assemblys which were more massive than the others (you tuck these away in a special pouch in case the situation arises where they will come in handy).
Your first throw is a bad one, and your dart strikes a rock rather than the caribou. The point shatters, the foreshaft is split, but your dart shaft survives intact. You ditch the broken foreshaft and point assembly, and you rearm the dart with a backup foreshaft from your pouch. You still have several darts in backup. While you've lost a point and a foreshaft, your mainshaft is just fine and dandy, and you haven't wasted time repairing darts. You don't have to contend with nibbling away at the lenth of the mainshaft of your darts (and thus the integrity of your finely tuned system) either.
Your 2nd throw is even worse than the first. It smashes into another rock so hard that the point is a gonner, the foreshaft is split like a toothpick, and even the mainshaft is damaged. You have extra darts handy so you don't worry too much for now. You hold onto the broken dart shaft. That evening around the campfire, you repair the broken mainshaft by removing the 3" of splintered end. You use a stone or bone drill bit (cone shaped to make a nice socket for a new foreshaft) between your feet and you spin the newly repaired shaft on the stone/bone drill bit, and drill a new socket. It only takes a minute or so. You take one of the more massive foreshaft/point assemblies, and attach it to the now shortened dart. The extra mass on the new foreshaft assembly makes up for the increase in spine of the shortened shaft, and your dart flies just as good as before.
Your next throw is just perfect. It drills into the vitals of a caribou and the caribou runs wildly before falling dead on the ground. Your dart shaft is broken in 3 pieces as the animal falls - completely useless ever-after. While butchering the animal later, you're careful to retrieve your forshaft and point assembly from the carcass. It's a bit slimy and it's a nice color red, but you figure correctly that it will work just fine (and if your superstitious, you might consider it even has extra hunting magic!).
Holy cow...I just scrolled up and realized that I got a bit carried away. I hope my point didn't get lost in all these words.
Does this make sense to you guys?