UK benchrest shooting at 100/200/300 yards uses the rules formulated by the World Benchrest Shooting Federation (WBSF). The Americans shoot to their own National Benchrest Shooting Association (NBRSA) rules & International Benchrest Shooters (IBS) rules. There is very little difference between these, which is handy as most of our equipment emanates from the USA. Our 600 and 1000 yard shoots are run to IBS rules.
RIFLES
There are two classes for both short-range and long range BR. For 100/200/300 yard shooting there are two weight limits - Light Class for rifles weighing no more than 10.5lbs. (c/w scope) and Heavy Class for rifles weighing no more than 13.5lbs. There is no restriction on scope-power and typically shooters will use from 36 - 45 power. Calibre is also unrestricted but 99.9% of shooters use the dominent 6PPC.

Typical 100 yard benchrest rig - BAT action, Tom Merideth stock, 36BR Leupold scope.
For 600/1000 yard BR there are again two classes - Light Gun for rifles weighing no more than 17lbs. all up and Heavy Gun for rifles weighing above 17lbs. A Heavy Gun might typically weigh 40 - 60 lbs. Scope power is again unrestricted and most competitors will use something between 25 and 45 power. Calibre is also unrestricted (subject to range safety limits) and, unlike short-range BR, the jury's still out as to which is the best calibre and there are a great variety of cartridges that will do the job. The 6.5x55 Improved and the 6.5-284 are popular in the UK. Big magnums are fine for the Heavy Gun class but touching-off 100 grains of powder can set up accuracy-destroying vibrations in a Light Gun.
Stock design is fairly liberal for the 600/1000 yard classes but for 100/200 yards, both stock and barrel-profile are 'tied down' by the regulations. However, if you purchase a fibreglass stock from any of the major manufacturers you can be sure it will comply. The width of the fore-end must not exceed three inches and the rake on the underside of the butt cannot be flatter than that made by a line drawn from a point 18 inches forward of the bolt-face to another point dropped four-inches vertically from the axis of the bore over the butt-plate.
Muzzle brakes are not permitted in short-range benchrest but they are allowed at 600/1000 yards - but only in the Light Gun class. Having said that, military-style muzzle-brakes which direct the blast sideways are not encouraged.
If you have a standard 'out of the box' factory rifle you will almost certainly find that it complies with these rules and can be accommodated in the UKBRA's Factory Sporter Class and we also run a Factory Sporter Class at 600 and 1000 yards. See section - 'The Rifles' for more details.

Here's a 600/1000 yard Light Gun rig. BAT action, Tooley MBR stock and Nightforce 12-42 BR scope.
RESTS
The rifle may be rested under the fore-end and butt on sand-bags. Bi-pods are not permitted as the rests must not be attached to the rifle. The front and rear rests must not be mechanically linked. Neither rest must be fixed in any way to the bench-top.
Our front-rests have come a long way from the simple sand-bags which were used at the very first benchrest competition. The front sand-bag is now a very small item, mounted on a substantial 'machine' rest, which permits movement for elevation and windage. The fore-end of a benchrest rifle is completely flat on the underside but must be no wider than three-inches for 100/200 yards. As a result, the front sand-bag is shaped to exactly accommodate the flat fore-end. Factory Sporter shooters may fit a three-inch wide plate to the fore-end to take advantage of these bags. At 600/1000 yards, the fore-end width is not restricted.
The rear bag may be made of leather or man-made fabric or a combination of both but it must not contain any metal. The bag may have 'ears' to guide the butt under recoil. To stabilise the rear bag so that it sits securely on the bench, another 'doughnut' type bag may be placed beneath it.
The rests for 600/1000 yard benchrest are very similar and in fact, many shooters use the same equipment.
Front and rear bags must be filled with pure sand. Many shooters use a 'heavy' sand called Zircon which is much denser and thus adds stability to the set-up.
For pictures of rests and bags - see Other Equipment.