GNAS rules say:
BOWSTYLES
201. Introduction and General Rules The recognised bowstyles are given below.
Additional information is also provided where necessary within the Rules for each separate
archery discipline. The following general rules apply to
all bowstyles:
(a) Visual Aids.
(i) Field glasses, telescopes and other visual aids may be used for spotting arrows.
(ii) Prescription spectacles or shooting spectacles, provided they are fitted with the
same lenses normally worn by the archer, and sun glasses may be used. The
glass of the non-sighting eye may be fully covered or taped, or an eye patch may
be used.
(iii) No visual aid may be fitted with microhole lenses, or similar devices, nor marked in
any way which can assist in aiming.
(b) Accessories. Accessories are permitted such as limb savers, bracer, dress shield,
bowsling, belt or ground quiver, and tassel. Foot markers are also permitted but must
not protrude above the ground more than one centimetre.
(c) Broad-head, edged, bodkin, silver spoon and any other large diameter arrow piles are
not permitted.
(d) An archer’s equipment must not represent an undue obstacle to other archers on the
shooting line.
206.
Longbow
(a) Bow. The bow shall be the traditional
longbow made from wood, either “self”, “backed”,
or “laminated” with cambered (stacked) belly and horn nocks. With the exception of the
“self” bow, each limb of the bow shall form a single simple curve from the handle to the
nock when at full draw. The bow shall be not less than five feet in length for an arrow of
less than 27 inches and; not less than five feet six inches in length for a 27” or longer
arrow, this being measured along the back between the string nocks. At no point shall
the depth of the bow, measured from back to belly, be less than 5/8 (five eighths) of the
width of the bow at the same section. The bow may carry no support for the arrow.
Bows of bamboo, constructed in conformity with the above, shall be permitted.
(b) String. The string may be of either natural or man-made substance, and may, if
desired, embody a “kisser” at any point as required to facilitate a consistent draw
position, but for no other purpose.
(c) Sights and Ground Markers. A sight, as such, is not permitted but one of the following
may be used:
(i) A mark on the bow limb.
(ii) A rubber band of no more than 1/8” in depth and thickness.
(iii) A ground marker of any design provided it does not exceed a height from the
ground of 6 inches or a diameter of 3 inches or impede any other archer.
(d) Arrows. Arrows shall have wooden steles (shafts), shall be fitted with feather fletchings,
and may have either horn-reinforced, self or applied nocks. There is no limit to the
maximum shaft diameter. The pile shall not exceed the diameter of the shaft at the point
of fitment. Shouldered piles, whilst not disallowed, should be avoided because of
excess damage to targets. Arrows shall be properly marked, so that there shall be no
difficulty in claiming them.
(e) Hand Protection
(i) Finger protection in the form of finger stalls or tips, gloves, or shooting tab or tape
(plaster) to draw, hold back and release the string is permitted, provided that such
protection does not incorporate any device to hold, draw and release the string.
(ii) A separator between the fingers to prevent pinching the arrow and/or a platform
tab may be used. An extension so as to provide a greater angle, prior to release,
other than that achieved by the use of a normal tab, glove or other form of finger
protection, is not permitted.
(iii) On the bow hand an ordinary glove, mitten or similar item may be worn but shall
not be attached to the grip.
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Those are GNAS rules, I'm not sure where my BLBS rule book is (and it isn't online) so can't check that right now.