A blank round is a firearm cartridge without a bullet (or any other payload) attached. Where the payload would normally be installed, the neck of the cartridge will instead be crimped shut and sealed with wax.
Blank is generally only used in small arms, and then only to simulate gunfire for training purposes - in a few cases it may also be deployed from heavy weapons or ordnance, usually for the same purposes. Many heavy weapons will fire a "training round" rather than blank - which still launches a projectile, but replaces the projectile's payload with a charge of paint or a firework. In general, blank rounds are intended to be less dangerous than live ammunition, but are still far from safe as they still generate a muzzle blast and can still fire the wax plug or other wadding materials at a dangerous velocity over a significant distance1. As a result, most modern weapons can be fitted with blank-fire attachements which serve to restrict the muzzle blast, retain any solid material and ensure that enough propellant gas is recycled to work the weapon's cycling operation (assuming a semi or fully automatic weapon). Without a BFA, most self loading weapons will have a significantly increased rate of stoppages when firing blank. Note, as previously stated, that training rounds - as opposed to blank - are very much not safe at all: they still fire a round, albiet usually a lower velocity one and/or one with virtually no explosive (or whatever) on board, but it's still a solid object moving at high speed and you'll be lucky to regret being hit by it2. See also the wax bullet.
Another, increasingly marginal, use for blank is in the launching of rifle grenades, line bearing munitions and similar devices - in some cases these may be purpose built rounds, different to the blank used for training.
Obviously the blank round is a creature of the modern era - prior to the metallic cartridge, removing the shot from your powder and shot was normally a pretty trivial exercise - and even today, anything that uses seperate ammunition can still "fire blank" simply by neglecting to load the payload on top of the propellant.
Despite the beliefs of the cinema industry, blank and live ammunition look different, weigh different amounts and sound different when fired - civilians, unfamiliar with the sound of gunfire might not notice the difference but soldiers probably will, especially if they're familiar with the weapon being used.
Also relevant are drill rounds - these are completely inert and are used for training and practice in weapon handling and magazine charging during basic training. These do have a bullet attached, but no propellant or primer - and often have a fluted or otherwise distinctive case as well. As with training rounds (see below) part or all of the round may be painted a specific colour.
Game and Story Use
- As in the movie Dog Soldiers starting the PCs off on a training excercise, only for it to turn into genuine trouble, may mean that they start the game with blank, rather than live, ammunition.
- Unfortuantely, it will almost certainly mean statting up at least one calibre of blank rounds for your RPG of choice.
- Illustrate the concept of "idiot" to your PCs by having an NPC threaten them with a weapon fitted with a BFA (even if he has put live ball in it, it's liable to blow up in his face when he pulls the trigger).
- Likewise, attempts to intimidate with blank fire should give characters (or NPCs) with the appropriate experience a chance to notice the different sound.
- A very experienced user might well be able to feel the weight difference when a weapon - or magazine is loaded with blank rather than ball.
- A botched attempt at black market trading may leave the buyer holding a consignment of blank or training rounds rather than the live rounds they wanted - inspection should tell blank from ball with ease, but training rounds may require more specific knowledge to spot.
- If it helps, NATO traditionally paints training rounds UN blue. Look for mismatched paint where someone has painted over it.