The original IMI Galil had weighed up to 4.35 kg (9.6 lb) depending on its variant, and this weight was criticised by the Israel Defense Forces. The heavy weight was a result of IMI having built the Galil rifle from a machined all-solid steel billet action in order to increase the structural integrity and survivability of the weapon.
The Galil Ace has a significantly reduced weight. IWI redesigned the action to integrate the steel with polymer, which is much lighter than the fully steel receiver of the original Galil. While the upper receiver is machined steel, polymer has been introduced to the lower receiver of the weapon to reduce the gun's weight.
Last round bolt catch
Another addition by IWI to the original Galil is the last round bolt catch, for the versions of the ACE in 5.56mm. The bolt hold-open feature is a common request of military customers, to reduce reloading times during combat.
Long-stroke piston system
The rifle uses the Galil's long-stroke piston system. The long-stroke system is found in the M1 Garand, AK 47 (upon which the Galil's internal mechanism design borrowed heavily) and more recently in the Tavor.
The gas tube, unlike the AK 47 system, is mounted on the rifle via a dovetail slide machined on the receiver upper-front block. This avoids any movement of the gas block that can influence barrel vibration and thus degrade rifle accuracy.
IWI have sealed the internal mechanism of the gun, by the addition of a sliding vertical cover. As a result, the internal mechanism of the Galil is sealed and protected from the accumulation of dirt or sand.
The IWI Ace adopts the Galil Sniper trigger instead of the original Galil trigger, in order to improve accuracy compared to the standard Galil. This is a two-stage trigger, which IWI have modeled on the two-stage trigger of the M1 Garand.
According to American Rifleman, the two-stage trigger is "clean and smooth with a 4 lb. 13 oz. trigger pull according to a Lyman digital trigger gauge."
The barrel is chrome-lined, cold hammer-forged, with a 1:7" twist.
According to American Rifleman: "Although this rifle is clearly based on the AK design, it demonstrated a superior level of accuracy potential compared to several of its cousins. The best single group [at 100 yards] of 0.83” and five-group average of 0.98” was produced using the Federal Premium 123-gr. Power-Shok soft-point load” (testing done using 7.62x39mm 16 inch barreled variant).