In a visit to the headquarters of Task Force Helmand in Lashkar Gah, Mr Cameron also asked troops about the protection new vehicles are offering from roadside bombs.
"Do you feel now that if you did roll over an IED, the vehicle would be more robust?" he asked Lance Corporal Simon Howells, 28, of the Welsh Guards, from Dinas-Powys, who replied: "It feels pretty safe."
Sergeant Neville Haye, 36, of the King's Royal Hussars, told Mr Cameron that Afghan soldiers had learned "professionalism" from their British colleagues.
"They are very capable, we are working with them on a daily basis, shoulder to shoulder," he said. "They are starting to do their own operations, we are taking a back seat, staying back and offering them tactical help and advising them."
Sgt Haye, from Cumbria, said troops had not discussed military cuts with Mr Cameron during a 15-minute chat.
In talks with officials, Colonel Nabi Elham, Helmand's provincial chief of police, told Mr Cameron his police officers were "increasingly well-trained".
"Our Afghan national security forces are sustaining damage on the insurgents," he told the Prime Minister.
At the smaller Forward Operating Base Shawqat, in Nad-e-Ali, Mr Cameron toured troops' tented accommodation and lunched with soldiers.
The base borders a bustling bazaar which did not exist on his last visit two years ago amid fierce combat.
Troops praised their Afghan counterparts over a drink with the PM at the base's store and cafe. Company Sergeant Major Nathan Love, 37, said he told the PM: "Their soldiers are no different to ours... They are more than happy to go forward and push the Taliban back."
