Assault rifle and assault weapon are colloquial terms for any of various types of intermediate-power long guns. Originally a military term for the kind of fully-automatic rifles issued to soldiers for battlefield use, the term has recently been applied (for political reasons) to smaller semi-automatic guns. Arms manufacturers had for decades advertised the supposed resemblance of their civilian products to military weapons.
Some well known assault rifles are:
The typical identified mission of an assault rifle is to provide fire support at ranges to 200yds by ordinary troops. That is, it is designed for massed anti-personnel fire at short ranges with simple maintenance. Studies by the U.S. army indicated that most conflicts between soldiers occurred at ranges of 100yds or less.
As a massed military weapon, assault rifles share common features: light weight, good pointing (for unaimed "intuitive" fire), bayonet lugs (to provide lethality without ammunition), selectable fire rates, high reliability, large magazines, and simplified operation. Many lightweight civilian rifles provide similar features, but omit selective-fire and bayonet lugs.
Assault rifles' ballistics are designed to cause injuries rather than death, with the least weight of expended ammunition. The low weight of ammunition eases logistics, including especially air transport and pack weights. The propensity to injure rather than kill strains enemy logistics with medical care and evacuation- the formal justification. An intent to injure is also merciful, and this is important to many soldiers. Besides assaulting enemy logistics, injuries decrease an enemy's will to fight more than deaths. Mercy also helps soldiers to pull the trigger. U.S. Army studies indicate that fewer than 20% of soldiers cause more than 80% of enemy deaths.
The M-16 for example, uses a low-weight, high velocity round. The AK-47 uses a slow round with a shifting soft lead interior that causes it to tumble in flesh. In contrast, most hunting and sniping rifles use high velocities and heavy bullets that kill large mammals by hydrostatic shock alone.
Assault rifles often include a setting for full-automatic fire. Many military organizations limit troops' access to fully automatic fire, either by training or equipment, in order to improve aim and logistics. It is famously hard to hit targets with a fully-automatic rifle in a long burst. For examples of enforced limits, the fastest select-fire setting of the U.S. M-16A engages a complicated three-part automatic sear that fires "optimal" three-round bursts for each pull of the trigger. Also, an important improvement in most later models of Kalashnikov automatic weapons is to reduce the rate of fire, with rates below five rounds per second considered best.
Effects on Doctrine and Organization:
To reduce logistic problems, and still provide high rates of fire, most current military doctrines employ a "squad automatic weapon" used by one or a few specially-trained soldiers in a squad.
A significant capability lost with the adoption of assault weapons was sniping by ordinary troops. Russian and derived doctrines therefore include squad-level snipers.
Effects on governance
Bayonet lugs, flash-suppression, large magazines and selective-fire are the significant functional differences between an assault rifle and a low-powered, lightweight hunting rifle. These are not large differences. Large capacity magazines and flash suppressors are easy to install. Lightly trained persons can simulate selective fire with any type of repeating rifle, including old-west lever-actions. Bayonet lugs serve only dire military situations.
Thus, as one would expect, forces armed primarily with true assault rifles are relatively ineffective except against unarmed persons. Non-governmental organizations with expedient arms have successfully resisted them.
In the U.S., most civilian weapons labelled "assault rifles" lack selective fire. Their magazines contain ten rounds or less. They fire once for each pull of the trigger, and have no way to act as "machine guns." This allows owners to avoid paying the $200 treasury fee and licensing required to own a small automatic weapon in the U.S. The weapons threaten members of civil government simply because they are effective small arms. Many owners see this as a check on tyranny, and training for civil defense.