A group of five senators - including three Army veterans - are seeking answers from Army Chief of Staff Gen. Mark Milley about why the service does not allow polymer ammunition magazines during training or in combat.

The letter comes on the heels of a recent decision by the Marine Corps to approve the use of Magpul Industries Corp.'s signature - and very popular - polymer magazine.

"This month ... the Marine Corps approved the use of an upgraded version of these polymer magazines," the senators wrote in the letter. "It is our hope that the Army considers them as well, or is able to disclose what issues they've found with polymer magazines so that we can make the other service branches aware."

The letter was signed by Sen. Joni Ernst, R-Iowa, a retired Army National Guard lieutenant colonel, Sen. Tom Cotton, R-Ark., a veteran of the 101st Airborne Division, Oklahoma Sen. Jim Inhofe, who also is an Army vet, and Johnny Isakson, a veteran of the Georgia National Guard, and also signing on was David Perdue, both of Georgia.

In 2012, both the Army and Marine Corps banned the official use of polymer magazines, citing potential safety hazards stemming from untested ammunition magazines cropping up in combat theaters in Iraq and Afghanistan.

Since that time, the Marine Corps has conducted extensive testing through the Primary Inventory Control Activity (PICA) on a various magazines and ammunitions types, announcing this past December that Magpul’s signature polymer magazine was selected for use in training and combat.

"The Magpul GenM3 PMag was the only magazine to perform to acceptable levels across all combinations of Marine Corps 5.56mm rifles and ammunition during testing. That magazine has, therefore, been approved for use for both training and combat," Marine Corps Systems Command told Military Times.

The senators' letter highlights that the rigorous testing by the Marine Corps of Magpul’s GenM3 PMAG witnessed zero stoppages even among a multitude of ammunition types.

"Additionally, reports state they also reduce damage to the chamber face and feed ramps when using M855A1 ammunition. As our national debt approaches $20 billion, ensuring the longevity of these rifles is important," the letter reads.

The letter to Milley is intended to ensure the U.S. does not fall behind near- peer adversaries like Russia in maintaining a modern and effective fighting force, according to Ernst's office.

"We request a response as to why the Army has not approved any polymer magazines for use in combat, or in training, and an update on if the Army is considering approving them now," according to the letter. "After years of technology advancement for our soldiers, and your fellow service branches testing and approving this technology, it is my hope that the Army is also working to ensure its warfighters have the best equipment possible."