FORT BENNING, Ga. — The Maneuver Battle Lab spent four days evaluating a pair of sub-caliber training rounds for a shoulder-launched weapon used to engage armored vehicles from confined or enclosed positions to identify which one best prepares Soldiers to fire the real thing.

Fourteen Soldiers from 2nd Battalion, 29th Infantry Regiment, fired 9 and 20mm rounds in the AT4 Confined Space launcher and compared their effectiveness and suitability to the 84mm live version. The experiment took place May 24-27 at Duke Range.

The AT4CS is a lightweight, disposable weapon designed for single use, said Steve Howard, a project officer for the Maneuver Battle Lab's Soldier team.

"It is safely and effectively fired from confined space to defeat various military targets, including light-armored vehicles, at both near and extended ranges," he said. "(But) currently, there is not a sub-caliber training round for the AT4CS."

A standard AT4 produces a large back blast. The CS model, however, features a counter mass that could allow troops to fire safely and effectively within buildings in an urban environment.

Justin Strayer, a close combat systems analyst for the Soldier Requirements Division, said the AT4CS can be fired from a 12-by-15-foot room that has a 7-foot ceiling - without triggering any blast overpressure or back-blast hazards.

The Directorate of Training and Doctrine established the requirement for a sub-caliber training round to replicate the actual system's launch effects and trajectory when fired, Howard said.

"This could provide Soldiers with a more realistic training system," Strayer said.

The 9mm training round even includes a back-blast charge for added simulation to the live weapon.

"The sub-caliber trainers give Soldiers a duplicate of a live round without having to fire a live round," said Styles Underwood, a DOTD shoulder-launched munitions training developer. "That's just going to help the Soldier in combat."

It could mean considerable savings for the Army, too.

The cost of firing an 84mm tactical round is about $4,500, at least 100 times more than the two trainers, which are $40 to $50 each, said Anthony Sacco, a project officer with Project Manager Close Combat Systems who was among the observers from Picatinny Arsenal in New Jersey.

Soldiers in the evaluation said it's tough distinguishing between the live round and sub-caliber trainers.

"The amount of kick both of them had was about identical," said Sgt. Paul Baummer. "It would provide close simulation in training. The only difference was the point of impact with the live round."

Staff Sgt. Aleksandr Kulik said the 20mm round could be highly beneficial if used in basic training, where only a few Soldiers get picked to fire an 84 mm projectile from the AT4.

"After shooting a 20mm, I expected a bigger kick from the live one, but it was pretty accurate," he said. "If privates get to shoot this, it will give them an idea of what it's like to shoot a real 84 … The practice 20mm has the reality of the kick and back blast, and it's just as loud as the live one."

Project managers and training developers will use the experiment's results to help decide which sub-caliber training round gets selected, but they said it would be at least two years before either is fielded.