Thursday, August 29, 2013

Gas Station Souvenir Shootout

Hi all!

Here we go! Look at these beauties.
The other day I was around Grants, New Mexico and ran into one of my favorite gas station novelties, gas station arrowheads!!!  Ok so you may have seen them around.  A quick look at a few attributes indicates that most flake cores were conical(ish).  By rotating the stone core, these knappers produced a series of pointed(ish) flake blanks.  Most flake platforms had the ubiquitous copper smear and pronounced bulb of percussion.  These two attributes combine to indicate removal with copper tools through direct hard hammer percussion.  Next, a quick bench grinding for shape and drill press for notches and you have a shaped stone that represents the memories of a week spent touring New Mexico.
I was (perhaps rather morbidly) curious as to how the things would actually fly and if they would go through ribs or not.  We've seen how actual hunting projectiles rain death from the sky without mercy, so let's see what tinker-toy points do.  The field school students and I bought a bunch and set off to see what these points were all about.  Of course these are not meant for hunting, they’re souvenirs, objects that make memories of vacations tangible.  On the other hand, they will be traveling at about 85 feet per second, so there is one thing going for them.
Setting up with Dave 
One problem became immediately clear; the bases of these points were actually just the un-thinned flake platform.  I had made a deal to not take a single flake off of the points so I ended up with some gigantic hafts to accommodate these things.  I gave each point the works, pine pitch glue and a fiber wrap.  A few initial thoughts as to what might happen here: Just for fun we set a hypothesis that curved points would snap at the apex of the curve.  Next we suspected that the thin hafting elements that were carved out to accept the largest point bases would snap upon impact. Finally, we picked our favorite points, placed bets and set out on our way. Hey, betting and hypothesis testing go hand in hand, right?
Hey, not too bad.

Rigged up and ready to send

The Results

To my surprise a few points actually worked ok, not great, not good…but ok.  The hafting elements really took a beating.  As we suspected, the thickness of some of the points made us have to widen the haft too much and breakage happened at impact.  They didn’t all break though. I’m working on a test that measures the tipping point for haft breakage using a diameter/internal width of haft measurement.  Things are coming along on that but I need more darts.

The two impact marks from a curved point snapping

Most of the points bounced off of the carcass with minimal damage to the target.  A few made little wounds then snapped.  The curved points made some interesting damage patterns.  First, unlike our hypothesis, breakage on the curved points appeared to occur at the junction of the haft.  A slow motion camera would be awesome for looking at that!  A pattern seems to exist that upon impact the curved tip snaps and makes an initial wound with a secondary impact occurring as the hafted fragment hits.  Neither of the wounds were a big deal. 

dull wound edges made by gas station points

The bench-ground edges of the points mashed their way through the soft tissue between ribs and did more scraping than cutting within the wound path.  The wounds are rounded about the periphery of the opening in comparison to true hunting projectile that make a rotating lenticular pattern.  It makes sense that these points do not penetrate far and have dull wound paths.  Sharp points allow the momentum of a dart to continue through further than dull points that create more friction.

Overall it pays to outfit projectile points with sharp edges too, not just sharp ends. There’s probably a joke in there somewhere about staying sharp and edgy.

Happy Hunting.
These hafts are too thin

...what a surprise
clean lenticuar wound from a bifacial projectile point 

there was no way this rig was going to work, destined to fail

Bad bruise, yes. Dead? No

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