The Remington bolt-action rifle is deadly, but not for the reason you may think. As part of a settlement in a class action lawsuit, Remington recalled millions of its Model 700 and Model Seven rifles in 2014 for firing when they weren’t supposed to. On Sunday’s edition of 60 Minutes, Lesley Stahl talks with Roger Stringer, the father of a young man, Zac Stringer, who went to prison for killing his younger brother with a Remington 700 rifle. Zac was 15 at the time, and he’s recently been released for good behavior after serving five years of his 10-year sentence. He has maintained his innocence, saying that the gun went off without him pulling the trigger.

And he’s not alone. More than 20 people have been killed by Remington rifles that their users say went off without provocation. In the time since Zac Stringer’s conviction, Remington issued the recall, which lends credence to his claim of innocence.

The recall notice specifies that the culprit is the Remington trigger assembly known as the X-Mark Pro. It turns out that the X-Mark Pro triggers assembled between May 1, 2006 and April 9, 2014 could have been put together with too much bonding agent, according to Remington. Owners have reported that the gun can fire when switching the gun’s safety on or off.

This exploded diagram of a Remington Model 700 shows its X-Mark Pro trigger, part #46.

Ironically, the X-Mark Pro trigger was a replacement for the Walker trigger, one that Remington engineer Mike Walker patented in 1950 and Remington notoriously failed to replace for decades. Even Walker himself warned the company that it required additional safety precautions. After CNBC reported on this trigger malfunction in 2010, Remington responded, saying that the story was misleading and inaccurate. But since the company issued the voluntary recall of the X-Mark Pro, that argument loses some credibility.

This exploded diagram of a Remington Model Seven rifle shows its trigger assembly, part #44, removed.

The X-Mark Pro’s design eliminated the trigger connector, a tiny piece of metal that sat between the trigger and the sear in the Walker assembly. The sear is the bar that holds the firing pin back, and the firing pin is the piece that strikes a round of ammunition to discharge it. Owners claimed that built-up grease or grit could push the trigger connector out of alignment, causing the sear to get stuck in the firing position. This means that the trigger itself was bypassed altogether, causing the gun to go off as soon as the safety was switched off.

“Treat every gun as if it can fire at any time, whether or not there’s pressure on the trigger,” emphasizes the 3rd Commandment of Firearm Safety, which says that you shouldn’t trust the gun’s safety mechanism. Unfortunately, this was all too true for owners of Remington rifles with Walker triggers, and it turned out to be true for those with the newer X-Mark Pro, too.

But why did the X-Mark Pro, the Walker’s replacement, seem to have the same problem? Well, the answer isn’t so simple. While the design of the X-Mark Pro seems to be sound, an excess of lacquer during the manufacturing process caused the X-Mark Pro’s internals to malfunction. The “how” of that malfunction is still not something that Remington has made public, but the end result is that some of the Remington 700 and Model Seven rifles with X-Mark Pro triggers act like the old ones with Walker triggers. As frustrating as that conclusion may be, the good news is that as cases like Zac Stringer’s get more publicity, Remington has begun to respond appropriately to customer complaints.

Photos via Remington Owner's Manual, Flickr / ZORIN DENU