Sub-caliber round

A sub-caliber round is a round the diameter of which is inferior to the barrel diameter. An expendable sabot is used to expand the diameter to the full barrel width of the firing gun.

The most used sub-caliber rounds are flechettes and kinetic energy penetrator tank shells.

sub·cal·i·ber (sŭb-kăl′ə-bər) adj. 1. Smaller in caliber than the barrel of the gun from which it was fired. Used of projectiles. 2. Relating to or firing such projectiles.

40mm Subcaliber Devices

Given the expense and special safety considerations of some of the factory 40mm loads, some recreational shooters use subcaliber inserts to fire more common and less expensive ammunition. These are rounds with similar outside dimensions as a standard 40mm round with a "chamber" to fire smaller rounds. Some common subcaliber rounds are 12ga and 20ga shotgun rounds. While light loads don't seem to pose any specific problems, some caution should be used against heavy magnum loads or slugs harming the integrity of the rail mounting system or the receiver of the grenade launcher. One interesting thing about these shotgun caliber subcaliber devices is that there are numerous specialty 12 gauge rounds that emulate many of the expensive and collectable 40mm rounds. These may include but not be limited to the following:

• Flares • Shell Crackers • Rubber Buck • Beanbag • Barricade Rounds • Rubber Slug • Flechettes

There are numerous subcaliber rounds intended for use in skeet or trap shotguns and this writer found a little 20 gauge to .410 tube to use together to add yet another caliber to the M203 collection. There are also plenty of 26.5mm rounds on the market today and they also come in several types. Many of these are a very inexpensive alternative to the equivalent 40mm collectable rounds. They are usually reasonably inexpensive as the only commercial launchers are Com-Bloc flare pistols and don't have much "visual tactical appeal." The addition of a 40mm to 26.5 subcaliber device will open up the rounds available to include the following:

• White Single Star • Green Single Star • Red Multi Star • Illuminating Parachute • Blue Smoke • Black Smoke • Orange Smoke

One thing to keep in mind with any of these surplus subcaliber rounds is the makeup of the launching mechanism. Black powder is not uncommon and in order to properly care for your expensive, registered M203 (or M79 if that is your platform of choice) you need to clean thoroughly and appropriately for the presence of corrosive compounds.

Another interesting subcaliber unit we obtained for testing is called the "Hornet's Nest" and is available from Autoweapons.com. It fires ten .22 LR rounds from this single shell, all at once. It outwardly resembles a red anodized 40mm round with a blunt, flat tip. Close examination will reveal 10 separate and rifled barrels inside. They are loaded in the rear of the projectile and a striker plate covers them. Each round has a striker inside the striker plate. The end cap is loaded with a Large Pistol Primer and it is inserted into the M203 and fired in the same way as a standard round. When the primer is detonated it forces the striker plate forward and simultaneously fires the ten .22 LR rounds. If you never thought about recoil and .22 LR in the same train of thought, rethink it a little. Ten 40-grain projectiles at approximately 1,000 fps give you 400 grains traveling at the same velocity.

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Wikipedia