The US military’s efforts to upgrade its infantry arsenal appeared to get a boost last week, when a group of senators questioned two retired generals about the need for the change and the delays hindering it.

Both the US Army and the Marine Corps are reportedly looking to replace the M4/M16 rifle platform, in use in various forms since the 1960s, as well as the 5.56 mm caliber bullet, in response to concerns about their effectiveness on the battlefield.

The M4, and the M16 before it, is “a terribly flawed weapon,” retired Army Maj. Gen. Robert Scales told a Senate Armed Services Subcommittee on May 17. Scales said any improvements that could be made would only be marginal, due to shortcomings in the weapon’s operating system.

The range and stopping power of the M4 and the 5.56 mm round are both seen as underperforming their competitors. Studies have found that the 5.56 mm round is less lethal at the range of a typical firefight in Afghanistan during the US military’s more than 15 years there.