I awoke this morning with a healthy dose of skepticism brewing about that 401.1 fps reading from the chronograph.  To make matters worse, the Canadians had decided to grace us with one of their arctic blasts and the snow was coming in sideways for a couple of hours.  By mid-morning the sun made a begrudging appearance and the snow stopped.   It looked like a good time to try another shot and see if yesterday’s “record” velocity was even plausible.  Unfortunately the serving on the string was in disrepair  and after the shot we observed the situation seen below.

A few days ago ago I had one of my imaginary  Roman busy-bodies sitting on my shoulder warning me to take care of the string serving.  But did I listen…..

Probably this blow out of the serving happened during the power stroke because the velocity was down to 270.9  fps.  I am fairly certain this number from the chronograph was accurate because I had made a point of shooting my Kodiak air rifle through the screens several times before making the ballista shot.  The readings for the air rifle were a consistent 648 to 654 fps.  This is perfectly normal for this particular .25 cal air gun and gave me confidence the chronograph was working accurately.  The 270.0 fps on Firefly was disappointing of course, but at the moment I am considering it the result of the blown out serving.  One correction from yesterday  is for certain,  the draw weight for that supposed 401 fps shot was actually 5000 lbs,  not 4500 lbs as reported.  Apparently the zeroing dial on the dynanometer had been inadvertently rotated because it was reading 500 lbs when it should have been set at zero.

The target seen in the following video is in shadow,  and it is hard to make out all the action.  What we are seeing is today’s 270.9 fps shot, with its slow poke 7000 grain bolt and 1140 foot lbs, take on the 1/4″ mild steel plate that is installed on the rear of my sand trap.  Range is 53 yards.    20100308134735(1)

If you play this video on slow it seems as if the bolt is moving through the air at an angle with the tip down.  I am not sure what might be causing this.  Is it because the 2870 grain tip is too heavy for this length bolt and the whole projectile trundles along nose down?  Perhaps it is because the bowstring gives the tail of the bolt an upward flick at the end of the power stroke.   Maybe it is some perturbation coming from the damaged serving.  At the moment I have no explanation.

This quadrobate tip is made from hardened 4140 (about 40 RC), and penetrated the 1/4″ steel plate to a depth of 2 1/2″.  The tip also went through the piece of 3/4″ plywood behind the plate and stuck out the other side  1  1/4″  into the sand.  The photo below shows how the bolt tipped upwards at the moment of impact.  Not surprising because any slight downward  angle of the bolt would probably be magnified into a full blown spinning upset as the rear of bolt was forced upwards by the impact.

The one way trip experienced by this bolt must have been excruciating.  Note how the explosive deceleration caused the fins to slip their grooves and migrate forward.  I hope to be able to try another shot tomorrow morning when the light is coming in from the East.  (Assuming of course we can get the Canadians to cooperate.)  With a new serving on the bowstring,  we should be able to answer whether that 401 fps shot was for real, or just a figment of my chronograph’s imagination.  I suspect the later.