After much flopping around these last few days,  Firefly was finally made ready for some high energy shooting this afternoon.   Two shots were made before the light faded.   The stats on the first shot are:  bolt weight 6991 grains, draw length 38″, draw weight 4500 lbs., velocity 333.1 fps, energy 1722 foot lbs.    Specs on the second shot with the same bolt, are:  draw length 40″, draw weight 4700 lbs., velocity 337.9 fps, energy 1772 foot lbs.

Here is a video in real time of the second shot.  Range is 50 yards.    20100305173642

Yesterday the bundles had been loosened and then torqued back up to a level higher than I actually intended.  This became immediately apparent as the draw weight went up much faster than usual as the bowstring was being pulled back.   As can be seen in the video, the limbs had about another 20 degrees to go before  they would have been perpendicular to the stock.  In other words, these results were obtained with only about two thirds draw!  Given the high draw weights I decided not to chance pulling it back any further.   By sheer good luck,  the bundles turned out to be perfectly balanced even though they were taken to a higher torque level than they ever had before.

The bolt used here has a blunt tip 3/4″ across.  It punched through the top of my compound archery target (about 3″ of dense foam) on through 24″ of straw bale, and then blew through the 1 1/2″  fir on the backside, apparently stopped only by the tough plastic fins acting like a brake as they tried to squeeze through the hole in the wood.  Here are a couple of photos of the target.

The important advance seen with today’s shots is the huge jump in projectile energy.  The best Firefly has  managed before is around 1000 foot lbs.  Now she is churning out 1772 foot lbs.  The best my old Gallwey ballista could do was around 1150 foot pounds.   The inherent power of the inswinger design is finally beginning to surface.  In truth, I am still reeling from this dramatic increase in performance.  As I have long suspected, serious power with these machines is largely governed by introducing very high levels of torque into the bundles.  How much is a very high level of torque?  That is not such an easy thing to measure accurately because of the enormous amount of friction between the  washer and vernier plate as the twist is being applied.  My attempts to measure the force being applied to the tightening wrench for the washer,  have largely been a failure because the  reading on the dynanometer appears as an indeterminate spike only when the washer is actually moving on to its next station.  Suffice it to say, the torque now being applied to the bundles in the tuning process is a lot more than anything I have attempted before.  It seems wise to stay at this level and not push things too far right now.

The fins on the bolts I’m using probably need to be a bit bigger to counter a slight wobble in the bolt flight.   It may help to shorten the bolt by a couple of inches.  This will effectively increase the spine of the shaft and past experience has shown that this can help stabilize the bolt as well.

I could not be happier with today’s results.    Sure hope the Catapult Gods are pleased with all my labors.   Very tired,  must sleep now.