Glaser Safety Slug, Inc. is a small American ammunition company based in Sturgis, South Dakota (the same location as Cor-Bon). The Glaser Safety Slug, a frangible bullet, is the company's most well-known product. The company was founded in 1975, the same year as the Glaser Safety Slug was developed by Jack Canon and Armin Glaser.
The original round was a hand-made hollow point bullet filled with No. 12 birdshot (0.05") in liquid Teflon with a flat polymer cap. To improve ballistic performance a polymer-tipped ball round was introduced in 1987 and the current compressed core form was first sold in 1988. The formation of the polymer was also changed in 1994 to improve fragmentation reliability.
The company produces bullets in around twenty calibers, from .25 to .45 for pistols and from .223 to .30-06 for rifles. Each calibre comes in two forms, 'blue' and 'silver', the second having greater penetrating power due to the use of No. 6 birdshot rather than No. 12.
The projectile in the cartridge is of a much lighter weight than more conventional types of cartridges and so the projectiles always exit the bore at significantly higher muzzle velocities. The current bullet has a core of very tightly packed lead pellets. On impact the bullet fractures along manufactured stress lines in the jacket - imparting all the bullet's force very quickly rather than over-penetrating a target or ricocheting on a miss. The extremely light weight and fragility of the projectile make it unsuitable for long range firing or against protected targets. The bullet design can produce large shallow wounds in flesh while failing to pass through structural barriers thicker than drywall or sheet metal. However, the wounds produced by these cartridges fail to produce penetration of depth and quality in targets as do more conventional bullet designs that retain all or most of their mass in a single piece. Some suggest that this lack of penetration makes them, and other frangible ammunition suitable for use in environments where there is concern that a bullet that misses its intended target or passes through its intended target might accidentally strike a non-enemy. With this in mind, the United States Federal Air Marshals Service tested and used the Glaser Safety Slug extensively in the 1970s and 80s on board commercial passenger aircraft to defend against hijackers. Published reports indicate that Air Marshals are now issued SIG-Sauer P229 pistols with a 12 round capacity firing conventional jacketed hollow point ammunition in .357 SIG caliber.
Compared to conventional ammunition the rounds are very expensive (on the order of 15 to 20 times more). Because of their design some sources report that they are less accurate, that wounds vary greatly depending on impact angles, and that the bullet can lack the power to reliably cycle a semi-automatic pistol. Use of these cartridges in hand guns for defense/combat situations is controversial because some argue that a handgun simply does not have the barrel length or powder capacity to accelerate the super light projectile to the point that it can reliably produce wounds deep enough to incapacitate a person. Similarly, using these cartridges in a rifle against large game is controversial because of the poor penetration that is achieved. However, use of these cartridges in rifle calibers against human targets is less controversial, as some argue the cartridges do produce acceptably effective wounds in man-size targets while adding a certain safety benefit.