There’s their popularity for a start — they sure have that in common. Both playing double shows at enormous venues. Gigs that size were hens' teeth a few years back. Now two in each city — not to mention others by Kasabian, CMAT, David Gray — in the same week: it must be witchcraft.

How can such different music universes exist simultaneously? How can both draw such huge audiences? What makes you a metal head as opposed to a country fan? Are you born like that? Is it peer group pressure? Can you swap? Can you like both? Can you catch Country?

Scratch the surface, though, and it starts to get strange. Both Metallica’s James Hetfield and Zach Bryan were raised in what you might call “unusual” communities, and both lost their mums at an early age, Hetfield when he was 16 and Bryan when he was just 20 (although you could argue he’d lost her before that).

Hetfield’s family were strict Christian Scientists. It is a religion that believes prayer is stronger than medicine and works best without medicine. All well and good until someone gets sick. When his mum got cancer, they just prayed harder. Her tragic death has informed songs like And Justice for All and The God that Failed.

Bryan was a “navy brat” born in Yokosuka, Japan, in 1996, when his dad was stationed there with the US navy. His mum had alcohol problems even then, and although the family returned to Oklahoma for high school, his parents were divorced by the time he was 12. She was dead before his 20th birthday. His debut album, DeAnn, is dedicated to her.

But the navy was in Bryan, and he had signed up himself by 17. He was already making music and was honourably discharged by 25 in order to concentrate on that career. He speaks fondly of those years in a way that suggests it was at times as much of a family to him as his actual family was.

Both Hatfield and Bryan turned to music for salvation. Both used song writing to make sense of their lives and feelings. Both have forged bonds with their audiences that transcend the everyday. For both of them, music is the air they breathe.

I am probably a little more impressed by the Metallica journey than Zach’s. The metal bands had to create their own universe, forge a career in an industry where radio wouldn’t touch them with a stick. They had to find an audience the hard way, but once found, God has it been loyal. It has its own ecosystem now, but it wasn’t always like that.

Country is easier. In many parts of America, country is a form of religion. There are standards, recurring themes, respected heroes. Hitch your wagon to a train that says Cash, Nelson and Jennings, and people will listen to you. Mention the old boys, drinking and a pick-up truck and you’re quids in.

The bottom line is, of course, suffering. Life isn’t easy and troubles will find you in the end. That’s as true in Metal as it is Zach’s universe. The only real difference is your poison of choice, your wheels and your apparel. Nothing Else Matters or Something in the Orange, the choice is yours.

If I was trying to choose between a metal life or a country one, I think I’d go country. The songs are easier to write, facile almost, and theme wise — I miss my dad, my woman done me wrong, I love my car, and tonight the bottle let me down — are ones I feel I could get behind. They speak to me.

The clincher is the car. I’m not sure metal heads drive at all. Bikes maybe? A ’57 Chevy wins hands down.