Arrow speed from historical bows: Bergman 1988 study

In 1985 three archaeologists took six bows, a crossbow and a spearthrower to the Royal Ordnance range at Enfield and measured the initial velocity of every shot with optical screens. What comes out is a scale of performance running from the spearthrower up to the Asiatic composite.

The 195 gram dart thrown with the spearthrower left at 23 metres per second, and every bow in the test beat it. The short Sioux hickory bow, 24.9 kg draw weight and a 53 cm draw, sent a 30 gram arrow at 30 metres per second. The double-curved African bow, 24.0 kg, reached 35 with a 40 gram arrow of Egyptian style. The medieval yew longbow, 36.2 kg at an 81 cm draw, shot a 90 gram large broadhead at 43 metres per second and a 50 gram field arrow at 53. The sinew-backed Apache bow, at only 17.2 kg, sent a 28 gram reed arrow at 43 metres per second. The Egyptian composite of 28.8 kg, drawn 101.6 cm, ranged from 32 metres per second with a 90 gram arrow to 52 with a light 25 gram one. The Crimean Tartar composite, 27.2 kg, shot the 50 gram field arrow at 51 and a 25 gram target arrow at 60. The modern crossbow of 40.8 kg, used only to set the upper limit, sent a 13 gram aluminium bolt at 62 metres per second.

The comparison the authors put first is this one: the 27.2 kg composite shoots the same 50 gram arrow at almost the same speed as the 36.2 kg yew longbow, 51 metres per second against 53, and carries it over 90 metres further. Light arrows always leave faster, but heavy ones absorb a larger share of the stored energy. The most efficient bows have the lowest ratio of bow length to draw length: 1.5 to 1 for the Egyptian composite and 1.8 to 1 for the Tartar, against 2.1 to 1 for the Sioux and 3.4 to 1 for the African bow.

The measurements were taken by technicians of the Royal Ordnance Small Arms Division at Enfield, using an MSI velocity computer type 808, a type 759 remote control unit and type 758 skyscreens. The first screen stood three metres in front of the archer and the second three metres further down range: the projectile crossing both gave the flight time and therefore the velocity, which was printed directly.

Most of the bows were replicas built with the materials and techniques of the original bowyers, based on originals in the authors' own collections or in museums; the African bow was an original of unknown provenance. Each bow shot the arrows that belong to it, modelled on the originals, and this is a stated choice: the authors prefer to assess each bow in its normal use, at the cost of making direct comparisons less clean. For each one they report length measured along the curves, draw weight, draw length, the ratio of length to draw length, and arrow weight.

All the shooting was done by one of the authors, McEwen, and each bow was shot several times. The table and the graph give the highest velocity reached by each projectile, not the mean. Every bow, the crossbow included, carried a used Dacron string in place of the sinew, silk and hemp of the originals: the authors say so, and note that synthetic strings raise the speed slightly, but that since all the strings had seen service none was at its best.

The table gives the maximum of several shots, never the mean, and does not say how many arrows were shot with each bow. With no mean and no spread, small differences between two bows cannot be judged, and a maximum rewards the best shot of the series. The same person shot throughout, so release, actual draw length and hold do not vary, which helps the comparison between bows but makes it impossible to say how much those figures depend on the archer.

The arrows change from bow to bow, and the authors themselves write that this makes exact comparisons difficult. Dacron strings on every bow move the replicas away from original conditions, in a direction the authors acknowledge. Distances appear only in passing, 109 metres in one case and "over 90 metres further" in another, with no systematic range test at all.

One point goes unexplained: among the five longbow arrows, a 70 gram one leaves at 37 metres per second while the 90 gram one reaches 43, against the trend the table caption claims. The value is printed as it stands and nobody comments on it.

Finally, the subject of the study is archaeological. There is no modern target bow in the test, nothing on grouping, tuning or accuracy, and the comparison between bow and spearthrower concerns prehistoric hunting, not target shooting.

The value of these measurements, for an archer, is that they put an order of magnitude on what traditional tackle does, measured with serious instruments rather than recounted. A spearthrower sits around 23 metres per second; a plain wooden self bow between 30 and 43; a sinew-backed bow or a composite, at lower draw weights, between 43 and 60; a 40.8 kg crossbow at 62.

The figure that bears most closely on choosing arrows is the pairing of draw weight and mass. The same 50 gram arrow leaves at 51 metres per second from a 27.2 kg composite and at 53 from a 36.2 kg longbow: nine kilograms more draw weight buy two metres per second, because in the longbow a large share of the energy goes into moving long, heavy limbs. Within one bow, by contrast, dropping arrow mass always raises the initial velocity, while heavy arrows take away a larger share of the stored energy. That is the trade-off behind the choice of arrow mass, set out here in figures measured on ancient designs.

What the study does not say is everything else. There is nothing on accuracy, on grouping, on spine or on tuning, no modern bow in the test and no comparison between archers. And the conclusion the authors want to leave is one of method: each bow should be assessed in the context it was built for, not measured against the English longbow as though that were the unit of comparison.