Chris Ferrari was just 18 the first time he balanced a rocket launcher on his right shoulder and aimed it at a practice target.
"Your adrenaline's going and you're trying to focus on getting that round to hit, and then you go to squeeze that trigger and, you know."
The report is loud enough to burst the eardrums of anyone not wearing military-grade hearing protection. And the blast wave from the weapon is so powerful it feels like a whole-body punch.
"It's exhilarating," says Chris's buddy Daniel, a former gunner in the Marine Corps who asked that we not use his last name. "When you feel a concussive wave, it's an awesome thing. It fills you with awe."
It also may do bad things to your brain.
Studies show that troops who repeatedly fire powerful, shoulder-launched weapons can experience short-term problems with memory and thinking. They may also feel nauseated, fatigued and dizzy. In short, they have symptoms like those of a concussion.
It's still not clear whether firing these weapons can lead to long-term brain damage. But Chris and Daniel suspect that, for them, it may have.
While in the Marines, Daniel and Chris spent two years in the late 1990s firing a rocket launcher called the shoulder-launched multipurpose assault weapon, or SMAW.
They were a team. Chris loaded the rockets. Daniel pulled the trigger. Then they would switch places.
And together, they fired hundreds of rounds in training exercises around the world.
"That's me and Daniel at the base of Mount Fuji, posing for a picture with our SMAW," Chris says as he leafs through an album of photographs Daniel put together.
The SMAW is one of several modern weapons light enough for one person to carry but powerful enough to blow up a tank.
Daniel and Chris say they felt like their brains had been rattled every time they fired the SMAW. And they fired it a lot.
"Chris and I were incredibly good shots," Daniel says.
"We never missed," Chris adds. "We were always selected by our sergeant and our leaders to do the firing because they wanted to see the explosion, you know, they wanted to see the target get hit."
But as the two men fired the SMAW again and again, some of the thrill began to fade.
Every shot "felt like the world was caving in on you," Chris says.
The U.S. military limits the number of times troops can fire heavy weapons like the SMAW in a single day. But the limits are based on concern about hearing loss, not brain damage.
And 20 years ago, safety wasn't taken very seriously, Daniel says.
"I remember they were saying you're only allowed to shoot three of these things a day because it's, like, really bad for you," he says. "And then I would shoot three and then you [Chris] would shoot three. And then the guys 10 feet from us would shoot six and then the other team would shoot six."
Chris had a lot of headaches, and sometimes couldn't think straight after a day on the range. "You feel odd and you feel out of place and you feel exhausted and tired," he says. "But, you know, you're a Marine and you learn to put it away."
Until you can't.
For Daniel, that happened during a joint training exercise in Malaysia. Their platoon was still setting up, Chris says, "and all of sudden out of nowhere: Boom!"
Malaysian troops just a few feet away had fired an antitank weapon called the AT4. The blast wave hit Daniel hard.
"I was, like, absolutely dizzy," Daniel says. "I was absolutely disjointed. I felt nauseous, like I really felt like I needed to throw up."
So Daniel told his sergeant. "And it was just: 'Shut your face. Are you complaining? Why is everyone else OK and you're not?' "
Blast injuries overlooked
Back then, in the 1990s, the military pretty much assumed a fighter's brain was fine unless there was some external sign of injury.
That was because, at the time, no one really understood how an invisible blast wave could damage the brain without leaving a mark, says Tracie Lattimore, who directs the Army's traumatic brain injury program.
"The science wasn't up to speed," she says. "It just didn't exist."
But since 2007, Lattimore says, the Department of Defense has spent about a billion dollars studying traumatic brain injuries, including those caused by blast exposure.
At first, the research focused on bomb blasts, especially those from the improvised explosive devices that had become common in Iraq and Afghanistan.
But over time, Lattimore says, the military's research has expanded beyond IEDs to include the effects of blasts from weapons like the one Chris and Daniel shot.
"If you talk to us in a year from now, I think we're going to have exponential growth in our knowledge coming out of these current studies and our future studies," Lattimore says.
Eventually, that could help the hundreds of thousands of veterans who have fired these weapons in the past couple of decades.
But right now, people like Daniel and Chris have no way to know whether firing heavy weapons could have affected their brains.
Chris wonders whether all those blasts might be the reason he once landed in a military hospital for two weeks.
It happened after a weeklong training exercise in the California desert near Twentynine Palms. Thousands of troops took part and Daniel and Chris fired lots and lots of rockets. They also set off lots of explosives.
Several days after the exercise ended, Daniel noticed that Chris was awake in the middle of the night.
"He just got up and started walking out of the room in his stinking underwear," Daniel says. "And I was like, 'Hey Chris, what's going on?' And he was just kind of like looking through me."
"I don't remember it," Chris says. "But I know that they put me in the hospital and thought I had spinal meningitis or something."
He didn't. And the doctors never pinpointed another cause. They clearly thought something was wrong with his brain. But at the time, no one would have thought to ask whether the problem was caused by the weapons Chris had fired.
Chris's military career ended one morning when his platoon left on a bus and he didn't get on it. Ultimately, he got a bad conduct discharge.
It's been nearly two decades since Chris and Daniel fired the SMAW.
They've both settled in Northern California, which is where they grew up. And they both have symptoms that could be from a brain injury — or something else.
Chris has lots of questions.
"Why does this hurt on my body? Why do I feel lost? Why can't I concentrate on stuff as long [as I used to]?"
Chris also has trouble controlling his emotions, something he says wasn't a problem before his military service.
For Daniel, it's his memory that's the problem.
"I used to be photographic. Now I'm forgetful," he says. "I'm 40, that's ... I don't know, man. Maybe I'm getting old."
Both Chris and Daniel have problems with balance and orientation. For Daniel it can happen when he turns his head quickly or stumbles.
"I lose my spatial orientation," he says. "I don't know where I am. Vision gets blurrier. Even sound is kind of muffled."
These are common symptoms of damage to the brain's vestibular system, something that affects many people who have experienced a traumatic brain injury from a bomb blast or blow to the head.
Uncertain coverage for care
But Daniel and Chris were never in combat and never were injured in any obvious way during training. That means it's not clear whether they are entitled to care from doctors and hospitals run by the Department of Veterans Affairs.
Chris has never tried to get care from the VA. But Daniel has. And he learned that the VA doesn't have an obvious category for people like him.
Daniel had never connected his symptoms with his time as a Marine until he heard a radio story on NPR suggesting that certain military weapons might be powerful enough to give the shooter a traumatic brain injury.
"I went back to the VA and I said I want to be tested for TBI," he says. "And they said great."
They handed him a questionnaire. The first question asked where he had been in combat. But he hadn't been.
The second question asked: "Were you hit by an IED?" Daniel says it went on: "Was it a grenade explosion? Was a bomb dropped too close to you?" So I couldn't actually answer the questionnaire."
All he'd done was fire a rocket launcher in training exercises, over and over and over.
VA doctors see quite a few veterans like Daniel, says Dr. Joel Scholten, who's in charge of physical medicine and rehabilitation for the VA. He says the conversation usually goes like this:
"While I was training we fired a certain type of weapon. I felt dizzy or had some ringing in my ears after that."
Then Scholten asks if the veteran was ever near a bomb blast or took a blow to the head. Many say yes. And for them, VA guidelines call for a full examination for traumatic brain injury.
But for veterans like Daniel, coverage is uncertain. That's because there still isn't clear evidence that training with heavy weapons can cause long-term problems with things like memory, thinking and balance.
"These symptoms are what we call nonspecific," Scholten says. "So they're not unique to traumatic brain injury, and in fact there is no symptom that happens only with traumatic brain injury or concussion."
From a medical perspective, the lack of a box to tick is not a big deal. Treatments usually focus on improving a patient's symptoms, regardless of the cause.
"For instance, someone with cognitive or concentration impairments, we would focus our therapy on how to improve concentration," Scholten says.
But paying for therapy is another matter. The VA gives priority to veterans whose medical problems can be linked to their service.
And since military scientists still aren't sure whether firing a powerful weapon can have long-term effects, Daniel says the VA is sending him the bill. He's being asked to pay out of pocket for high-tech brain scans and other tests.
"I love the VA," Daniel says. "I have nothing bad to say about the VA. The individuals there get it. They really do. But their hands are typically tied by their process."
Studies now underway should help clear up whether people like Daniel could have been harmed by the weapons they fired, Scholten says. And the results of those studies will be used to update the VA's guidelines on who gets checked out for a traumatic brain injury.
"In the next iteration, will we or should we expand to include training exposures?" Scholten says. "Possibly so."
If they do, it could mean evaluating the brains of tens of thousands of veterans who trained with weapons like the one Daniel shot.