From the latest web published NBRSA 1,000 rules: (I don't see the bit that Wilbur mentioned. Evidently this is one of the differences between short range and 1,000yd.)
(b) HEAVY GUN.
(1) All shooters shall shoot from designated benches.
Shooting off-hand or from the prone position is not allowed.
(2) There are no restrictions for the rifle being used as to
weight or sights; caliber is restricted to .40 or less. Muzzle
brakes may be used, but they may not be of a “clamshell” or
any other design that exit gases to the rear. Rifles are fired
utilizing sandbag front rests, which may be supported on a
pedestal that does not co-act with the sandbag to restrict
upward and/or rearward movement. The rear rest is
comprised of a sandbag, which may be attached to a pedestal
and that supports the rifle between the rear of the pistol grip
and the toe of the buttstock.
(a) A sandbag is defined as a bag with or without a pedestal,
with a leather or cloth cover, that is capable of being easily
flexed by the fingers, and contains a dry finely divided
nonmetallic substance such as, but not limited to, sand, gravel,
or grain, without additive and packed loosely enough that the
bag can be easily deformed by pressure of the fingers. The
cover of the sandbag must not be bound in such a manner to
prohibit free movement of the contents. Lubricants such as
talcum powder, Vaseline, mica or friction reducing tape of no
more than .011” total thickness may be used on the bag for
lubrication.
2. RESTS & SANDBAGS.
(b) A front sandbag rest shall support the front part of a rifle;
a rear sandbag rest shall support the rear part of a rifle.
Neither rest can be attached to the bench, the rifle, or each
other. They must be movable in all directions independently of
the other. Any part of the rifle resting thereon must maintain a
minimum of ½ inch distance from any part of the retainer or
container holding the sandbag on which the rifle rests.
Whenever the rifle makes contact on its sides, there must be a
minimum ½ inch thick sand on each side. Sandbags on front
rest must be a minimum of 1 ½ inches wide by 4 inches long.
Rear rest sandbags must be a minimum of 1 ½ inches wide by
3 inches long. No device of any kind can restrict the upward
and/or rearward movement of the rifle. Any sandbag used as
a rest that is not supported by a retainer and that has
movement without restraint need not comply with this rule.
(c) Rests, rest changes, or recoil systems must comply with
rule “K.2.(b)” (above) and be shown to and approved by the
rest committee and/or Range Officer before being used in
competition. Rifles must rest on sandbags and slide on
sandbags only; no multiple recoil (“return to battery”) systems
on front or rear rests are allowed.
