The Ballista

……ZZZZZZZZZzzzzzzzzzz…… 400 yards…….. rolling green fields………… click, click, click………… must make truck tie-downs for Firefly…… must start long range testing…… zzzzzzzzzzzzz…..
(stage directions: Eyelids flutter, rolls over, mumbled cries for coffee)……

Oh! God! He’s waking up………

The following posting is an updated listing of the shots made since installing the latest set of limbs, the Mk. VIII’s. It is a bit of a dog’s breakfast, I know, but such is the nature of tinkering.

The first 4 shots are done with a 7,000 grain bolt with a 6 1/2″ quadrobate tip. Velocity readings were taken with a RADARchron, microwave based, Doppler chronograph. Accuracy +/- 2%. All shooting is done at 55 yards (50 meters) unless otherwise noted.

Shot # Velocity Comments

1 204 fps ?? I was pretty well disorganized for chronographing this first shot. Reported by memory that this shot was 240 fps. Now think that I transposed the 4 and the 0. My bad. Corrections made.

2 190 fps Very weak due to leaving it cocked to stretch the bundle. Limb can be hand pulled 1/2″ off stanchion at rest.

3 210 fps Started torsioning sequence by adding 7 1/2 degrees all around. Draw weight 2900 lbs. Limb can be hand pulled 3/8″ away from stanchion at rest.

4 219 fps Now at 15 degrees past starting point. (i.e. +15) Limb can be lifted 1/4″ off stanchion by stout hand pull at rest. Draw weight 3300 lbs. Starboard limb shows to be tracking above its target plane of movement. Will introduce some asymmetrical tightening to train it into position. Top half of starboard bundle will receive additional torsion.

Let’s reorganize this presentation a bit:

Shot # Velocity. Draw Weight. Draw length. Washer rotation & comments.

5 220 fps 3400 44″ Starboard top +22 1/2 degrees, the rest at +15. Limb can still be hand lifted 1/8″ off of stanchion. We are now using a different style of bolt. Weight 6867 grains, 26 1/2 long, 1 1/2″ flat tip. All following shots will be performed with this bolt until announced otherwise.

6 177 fps 3300 lbs 44″ ST + 30, SB +22 1/2, PT +15, PB +15. (ST = starboard top. PB = port bottom. etc.) This shot was wildly out of balance with the starboard side limb perhaps retarded twenty degrees behind the port side limb due to its stiffer resistance. The shot flew far left, about 10 feet at fifty yards. Velocity clearly terrible. Bowstring rates as loose, with noticeable slop and zero twang in the at rest position.

——- A tight string is key to speed. A ballista with a loose string has a dull and thudish sound to it. One with a tight string emanates a much higher tone. ———

For obvious reasons, I am holding off shortening this string until the torsioning sequence is complete.

7 205 fps 3600 lbs 44″ ST= +30, SB +22 1/2, PT +22 1/2, PB +22 1/2. Bow string is too loose.

8 201 fps Rest same as above.

9 196 fps Rest same as above. Torsion balance in these last 3 shots was excellent. Bolt leaving machine directly over the bolt groove. All three shots were casually aimed yet grouped inside a one foot circle at fifty yards. Remarkable given that the bolt flight appeared imperfect, with a noticeable tail waggle for the last twenty yards. Bowstring slack and needs to be shortened by at least 1″ before continuing. No longer possible to manually pull the limb away from the stanchion at all. Mk VIII limbs rate as nominal. Zero strain damage evident.

10 251 fps 4050 lbs 44″ All positions +30. Bow string complete bollocks. Bolt too short by perhaps 6″. However, the bundles are nicely balanced and the bolt lifts off directly over the bolt groove. The limbs track A-Okay inside their target planes. Previous trials with Firefly have shown that if we increase the draw weight to 5000 lbs we can reliably get velocities of around 320 fps with a 7,000 grain bolt . If I can get these heavier (and seemingly reliable) limbs to kick out a steady 300 fps with 7,000 grain bolts, then the power levels will be sufficient to conduct some serious accuracy trials. Only accurate ballistas are interesting. Sorry Whelan.

11 275 fps 4o50 lbs 44″ All positions +30. Only change over the last shot was that I shortened the bowstring by about an inch. String is noticeably more taut in the at rest position. Need to order more double braid for some strings. Desperately need to make more bolts. Limbs happy.

12 299 fps 4250 lbs 46 1/2″ All positions still +30. The extra 2 1/2″ of draw length I included this time seems to have boosted us into the velocity envelope I want for this next series of tests. Limbs remain trouble free. Bolt and string still very much sub-par. Hand cocking to this length and weight of draw is quite a chore for one average man to handle. I’m betting a machine this size had a minimum of two really strong, big guys, at the levers.

A brief pause ensues while I make some more bolts and dream about strings…….

13 200 fps 4100 lbs 44″ All +30. New bolt was tried. Weighed in at 8889 grains. Christened “Little Walloper”. Power down probably due to loop slippage in bowstring.

14 285 fps 4100 lbs 44″ All +37 1/2 degrees. Old bolt that weighed 6867 grains Bowstring shortened by 1 1/2″ and holding firm. Starboard limb tracking high; believe may be related to the waggle tailed bolt flight. May need to try longer shafts too.

15 210 fps 3700 lbs 39 1/2″ All +37 1/2 degrees. This shot made with “Little Walloper”, 8889 grain bolt. I am not convinced that increasing the weight of the bolt is actually picking up any more foot pounds of energy. I will make up three new bolts (5,000 grain, 7,000 grain, and 9,000 grain) . Firefly finally seems to be reliable enough for some extended experiments.

16 287 fps 3700 lbs 36″ draw length. New bolt that weighed 6,651 grains. ST +45 degrees, SB 30, PT +37 1/2, PB +37 1/2. The starboard limb is tracking better after tightening the top and loosening the bottom of its spring bundle. Bolt flight was good. Draw length shorter than previous shot #15, yet pull weight is the same. Go figure …. that kind of thing happens after adjusting the bundles.

17 245 fps 3700 lbs 36″ draw length. This shot made with “Little Walloper”. Bolt flight good.

18 260 fps 3700 lbs 36″ draw length. Back to the 6,651 grain bolt. Bolt flight excellent.

19 258 fps 3700 lbs 36″ draw length. Same as above and also went through the same hole as the previous shot.

20 208 fps 3400 lbs 33 1/2″ draw. 6,651 grain bolt. Hit about 1 foot below aiming point on cardboard target. Range is fifty five yards and I will attempt to shoot a group. Velocity is low due to reduced draw and pull weight. Suspect the loops may have slipped again.

21 210 fps 3400 lbs 33 1/2″ draw. 6,651 grain bolt. This shot struck three inches to the left of the previous shot # 20.

22 205 fps 3400 lbs 33 1/2″ draw. 6,651 grain bolt. This shot disappeared into the same hole made by shot #20.

23 185 fps 3400 lbs 33 1/2″ draw. 6, 651 grains. This shot went through same hole as shot # 20 & 22

24 196 fps 3400 lbs 33 1/2″ draw. 6,651 grains. This shot went through the same hole as #20 & 22 & 23. Accuracy at this power setting is outstanding. The limbs are finally tracking in their proper planes and the bolt flight looks near perfect. Couldn’t be happier with these last five consecutive shots at fifty five yards.

25 282 fps 3400 lbs 33 1/2″ draw. 6,651 grains. ST +52 1/2 degrees, SB 37 1/2, PT +45, PB +45. All positions have been advanced by 7 1/2 degrees. That appears to be all it took to boost the velocity by 80 fps. Also, this is the first shot after the sights were adjusted to move the group onto the bulls-eye. Some good luck going on getting that right. Drilled it.

26 278 fps 3440 lbs 33 1/2″ draw. 6,651 grain bolt. Decided to spice things up a bit by taking a bead on that coconut that has been waiting patiently in the fridge these last nine months. Click for vid. 201110221249222 All these shots have been witnessed by the Rebecca. More witnesses will be needed for the work that is to come. There is just too much work to have gotten this far, to have it questioned by an unverified reporting of the facts.

27 283 fps 3400 lbs 33 1/2″ draw. 6,651 grain bolt. First sighting shot of the day. Struck 2″ right of where intended. My flub.

28 279 fps 3400 lbs 33 1/2″ draw. 6,651 grain bolt. Second sighting shot. Drilled it.

29 286 fps 3400 lbs 33 1/2″ draw. 6,651 grain bolt. Showtime! Nailed the cone. Can’t believe the Gods are being this good to me.

30 274 fps 3350 lbs 33 1/2″ draw. 6, 651 grain bolt. Sighting shot on original group. They just keep disappearing into the hole from the previous shot. I am a dyed in the wool target shooter from way back, and I must say, this string of shots is really quite extraordinary. The limiting factor on the accuracy of this machine, appears to be the precision with which I can align its sights. Group size is match grade. Overall size of this 11 shot string is 3″, range 55 yards (50 meters). However the last three shots have literally gone through the same hole. This phenomenon is obviously a gift from the Gods and I am resolved to make not the slightest change in her tuning for a while. I have fabricated and tested over fifty flintlock firearms, many modern, and not so modern, rifles and pistols, and I must say, keeping in mind her obvious limitations as a catapult, shooting Firefly reminds of the very best target grade weapons I have tested. Absolutely extraordinary.

…But I digress.

31 269 fps 3350 lbs 33 1/2″ draw. 6.651 grain bolt. That makes the last five through the same hole. I went to the doctor today and my blood pressure is uncharacteristically high. These last few days have been very jacked for me. I know this sounds like hyperbole, but I am literally getting a sustained adrenaline dump from all this success. Sorry to be such a boor, but I just feel like a door that I’ve been knocking on for a very long, has suddenly opened. I’m blinking a bit.

32 270 fps 3350 lbs. 33 1/2″ draw. Ditto. This is getting weird.

33 215 fps 3350 lbs. 33 1/2″ draw. Needed a change. This shot made with “Little Walloper”. Hit low from the previous shots by a couple of feet. It looked a bit ponderous. BP down.

34 210 fps 3350 lbs. 33 1/2 ” draw. No zip, trajectory noticeably curved. Boring.

35 270 fps 3350 lbs. 33 1/2″ draw. I used a new style bolt here. Weight is 6,693 grains. Fins are a bit longer, with a classic angled rear end. It hit about 5″ above the previous points of impact. Sights have been adjusted to compensate.

36. N/A fps 3350 lbs. 33 1/2″ draw. 6,693 grain bolt. This is my second ice cream shot. Results as follows: click for vid. 201110211431001 BP up.

37 260 fps 3350 lbs. 33 1/2″ draw. 6,693 grain bolt. Sighting shot. 12 o’clock, 2″ from dead center.

38 263 fps 3350 lbs. 33 1/2″ draw. 6,693 grains. Sighting shot. 12 o’clock, 3″ from dead center.

39 N/A fps (est. 260 fps) 3350 lbs. 33 1/2″ draw. 6,693 grain bolt. This was the my first shot in a three shot string testing off hand accuracy. 1 o’clock, 2″ from dead center. Good clean control of the aim and trigger pull.

40 N/A fps (est. 260 fps) 3350 lbs. 33 1/2″ draw. 6,693 grain bolt. I blinked at the moment of release, trigger control was spotty. 3 o’clock, 4″ from dead center. Second offhand shot

41 N/A fps (est. 260 fps) 3350 lbs. 33 1/2″ draw. 6,693 grain bolt. 12 o’clock, 1″ from dead center. The current sight setting is set 1 1/2″ high at 55 yards when using a 6 o’clock hold. Bulls eye diameter is 4″. No blink this time, follow through was right on, trigger pull excellent. This one felt really good. Third offhand shot.

42 N/A fps (est. 230 fps) N/A lbs. Ditto on rest. Something is wrong. No chrono reading, but velocity clearly down. Struck in the dirt 12″ low. String a tad slack, not so sure it was loop slippage this time. A mystery to investigate. I need to start adding the date to these shots. Above four shot string done on 10/23/11. It looks like this blog posting will be the place I come to record all the raw shooting data.

43 through 50. Various sighting shots that concluded with that trick shot picking the apple off the pumpkin.

50 through 75. It is 11/04/2011 and this entry is a catch-up to at least record the existence of 25 sighting and tuning shots made with Firefly over the last couple of weeks. No attempt was made to measure velocity as I need to redo the mounting bracket for the chronograph and have yet to find a suitable way to remove the 30 second time limit for making the shot.

76. 11/07/2011. This is the first shot after realigning the stock to the field frames to remove the string/deck gap. It hit 15″ to the left of the bull. Port bundle, top half, needs 7 1/2 degrees more twist.

77 through 80. 11/10/2011. Goofing around to establish a line of flight that coincides with the line of the bolt groove.

80 through 94. 11/15 2011. I removed the bronze hard stops to insure that the string always remains taut in the at rest position. The 6,693 grain bolt showed an average velocity of 300 fps with a 10 fps variance range.

94 through 100. 11/16 2011. I tried out a new, lighter weight bolt (5,825 grains) and the velocity jumped up to an average of 347 fps, with one shot that registered 358 fps. I still seem to get the occasional waggle tail.

101 through 105. 11/20/2011. I took the 5,825 grain bolt and cut new grooves for the two side fins. Now these fins are positioned so that they are just touching the flight deck. This arrangement causes them to act like training wheels to prevent the bolt from having any axial rotation as it trundles down the bolt groove. It will take a dozen or so more shots to know if this has cured our randomly occurring waggle tails. Velocity is now averaging 335 fps.

106. 11/21/2011. 306 fps. 5, 825 grain bolt. I tried putting a 6″ strip of double back tape on the bolt groove. The hypothesis being tested was that the bolt was perhaps being bumped forward by the initial impact of the bowstring. The tape was supposed to retard this forward bounce. Apparently all it did was to cut the velocity by 30 fps or so.

107 through 110. 11/21/2011. 5,825 grain bolt. 351 fps, 351 fps and 348 fps respectively. For these shots I waxed both the flight deck and groove and also the bolt itself with a liberal amount of simonize floor wax. This appears to have increased the velocity by 15 fps. No waggle tails yet. Also, accuracy has been at our nominal group size of 3″ at 50 meters for shots 101 through 110, (excepting 106). I have removed the dynanometer for now, but there is no reason to think the draw is not still 3700 lbs. at the 33 1/2″ draw length.

111 and 112. 12/03/2011. Two shots on Porcus Maximus with a 6500 grain Dura quadrobate. Velocity 305 fps. Impressive vids., lucky on the sighting and shooting. A wind of 15 mph from the North for shot 111. No apparent drift issues when the same shot was attempted in zero wind the next day (shot 112) , same bolt and ballistics etc. Conclusion: a 15 mph wind has negligible effect on the lateral dispersion of the shots at fifty yards. Pattern testing on cardboard, needed to confirm.