“Small-Bore shooting…” is a reference to the diameter or calibre of the ammunition used.
The concept of small-bore or miniature rifle ranges was introduced by the military for training purposes to improve the marksmanship skills of the troops at the same time using less costly ranges, firearms and ammunition than the military standard Full-Bore (.303 inch) centre fire calibre.
For the majority of todays small-bore shooting disciplines “small-bore” means .177 inch (4.49mm) diameter airgun pellets or .22 inch (5.56mm) diameter long rifle (LR) rim fire cartridge ammunition.
Many will be aware of .22 inch airgun pellets and these can be used in some competitions but this calibre is more usually used for field sports and hunting where the additional pellet weight is of benefit. The muzzle energy is the same for both .177 and .22 air gun pellets.
In our shooting disciplines “Air” means .177 inch diameter wad cutter or dome headed style pellets.
Air rifles and pistols can be categorised into three main groups depending on firearm technology. These are break barrel (or springer), pre-compressed pneumatic (PCP) or CO2. By far the most common types these days are PCP and springer.
PCP firearms rely on air held in a cylinder mounted on the firearm and compressed to some 200bar (or 100 times the pressure in a car tyre). Handling and charging PCP firearms requires considerable respect on behalf of the user and suitable training will be provided to all newcomers.
Break barrel firearms use a spring driving a pump style piston. The action of “breaking” the barrel compresses the spring and sets the piston ready for release by the trigger mechanism.
In order to comply with the Firearms Act the muzzle energy of air rifles is limited to a maximum of 12 ftlbs and air pistols to 6 ftlbs. Anything more is illegal and BSB R+PC will not allow its possession or use on club premises. For normal day-to-day shooting the set point for a firearm is usually comfortably below this limit to ensure the firearm remains legal at all times. Periodic recalibration and certification by a reputable firearms dealer is recommended.
CO2 firearms employ a small disposable cylinder of compressed gas very similar to those used in the old fashioned soda water bottle.
LR or 0.22 Long Rifle ammunition comprises a lead bullet crimped into a brass cartridge case that also contains a main charge and a primer. So called “Live” ammunition. The term LR is used to distinguish the length of the cartridge from short rifle ammunition, sometimes used in pistols.
For small-bore the primer is contained in the cartridge rim, hence the often used term “rim fire”. (This differs from full-bore, centre fire, where the primer is held in a cap centred in the base of the cartridge.) When the trigger is released the firing pin hits the rim, this ignites the primer which in turn ignites the main charge. Combustion within the cartridge almost instantaneously builds up a high pressure that is eventually sufficient to overcome the grip of the bullet crimp or cannelure and the bullet is released down the barrel.
Because of the increased energy generated in the cartridge and the inherent danger of injury to others the possession of LR rifles and ammunition is subject to the holder obtaining a Firearms Certificate.
Rifling is a spiral groove or “land” along the entire length of the barrel that causes the bullet to spin like a gyroscope making it more stable in flight, less affected by wind and resistant to tumbling end-over-end. Air rifles and pistols also have rifling for the same reason. By comparison shot guns are “smooth-bore” firearms without spiral lands.
(Typical values – Unit conversions are indicative, for information only.)
|Ammunition Diameter||Muzzle Energy||Bullet Mass||Muzzle Velocity|
|Air – Rifle 0.177 inch (4.5mm)||12 ft lbs (16 Joules)||8.5 grains (0.55 grams)||760 ft/s (230 m/s)|
|Air – Pistol 0.177 inch (4.5mm)||6 ft lbs (8 Joules)||7 grains (0.45 grams)||500 ft/s (150 m/s)|
|LR – Rifle 0.22 inch (5.6mm)||101 ft lbs (138 Joules)||40 grains (2.6 grams)||1080 ft/s (330 m/s)|
Muzzle Energy Calculation:
Using imperial measures, muzzle energy is often expressed in “ft lb” (“foot pound”) although more correctly it should be written as “ft lbf” (“foot pound-force”). In practice this makes no difference to the values we see but the distinction between “weight” a force and “mass” is necessary to follow the calculation below. “Weight” is equal to “mass” times “acceleration” and on the surface of a planet, acceleration is provided by gravity.
Here’s the calculation:
ft lbf = m x v2÷ (2 x G x 7000) ”
or = grains x muzzle velocity x muzzle velocity ÷ (2 x 32.16 x 7000)
or = grains x muzzle velocity x muzzle velocity ÷ 425240
m = mass of the bullet in “grains” (1 lb = 7000grains)
v = velocity. In this case muzzle velocity (feet per second)
G = acceleration due to gravity (32.16 ft ÷ s2)
s = second
ft = feet
lb = pound weight ( lb = lbf x G, or lb = lbf x 32.16)
lbf = pound force ( lbf = lb ÷ G, or lbf = lb ÷ 32.16 )