Cpl. Matthew Wilcox claimed he fired his gun in self-defence. (Andrew Vaughan/Canadian Press)

A Nova Scotia reservist convicted in the 2007 shooting death of a comrade in Afghanistan is facing "cruel and unusual punishment" because of the limited penalties available under military law, his lawyer said Wednesday.

Cpl. Matthew Wilcox, from Glace Bay, was convicted in July of criminal negligence causing death and negligent performance of a military duty for shooting Cpl. Kevin Megeney, 25, of Stellarton, in the chest at Kandahar Airfield.

The criminal negligence charge carries a maximum sentence of life in prison, while negligent performance of a military duty carries a maximum sentence of two years less a day in jail.

In the first day of a three-day sentencing hearing, Wilcox's lawyer, Maj. Steve Turner, argued the range of punishments available to the court are unconstitutional, citing a previous ruling from the Court Martial Appeal Court that found the military justice system is harsher than it needs to be.

"I'm arguing cruel and unusual punishment," Turner told the military judge, Cmdr. Peter Lamont.

There were 25 prosecution witnesses and 90 exhibits at the trial. Wilcox was the only defence witness.

Wilcox, 24, testified he feared for his life when he heard a weapon being cocked and fired his gun instinctively on March 6, 2007. He said it was only when he saw the body on the ground that he realized it was Megeney, his tentmate.

The prosecutor told the four-person military jury that Wilcox's claim of self-defence was not credible and that both soldiers were playing a game of quick draw. The jury deliberated for about two hours before finding Wilcox guilty on the two charges. It found him not guilty of manslaughter.

Michel Drapeau, a retired colonel and now a lawyer in Ottawa, doubts there will be a lengthy prison sentence. He said the nine-week trial and the loss of a close friend may be punishment enough for Wilcox.

"He could face dismissal with disgrace or just plain dismissal, but I would be surprised if he were given any of these two sentences because they do carry a very significant lifetime stigma," Drapeau said.

There is even a slim chance that Wilcox might not be kicked out of the Armed Forces, Drapeau added.

With files from the Canadian Press