Musket injury information needed

Good evening

I am an author of historical crime novels, and the narrator of my new series is a veteran of the Peninsular War. (That’s not the core of what I am writing, but I want to be sure that I have an accurate back-story for him.)

I already know that I want him to have been present at the Battle of Albuera in May 1811. He is a soldier servant to an officer and takes care of horses. At the battle I want him to be injured – not fatal, and a disfigurement only. (For my later purposes, he cannot be disabled – he needs to be able to ride and run.) It has been suggested to me that his face could be burned and eventually badly scarred by the recoil from a musket. I have come across this article, which contains a couple of images that show what might have happened to him: https://www.military-history.us/2017/09/muskets-at-the-battle-of-waterloo/ (Different battle, but I think it’s similar.) But what I am struggling with is whether such a lowly soldier would have had a musket. He’s serving with the 48th Northamptonshire Regiment. Would he have had his own weapon, or might he – in the heat of battle – have picked up one from a fallen soldier? And if the latter, would he have known how to use it?

Many thanks for any clarification. As I say, I am not going to dwell on his military service (except in occasional flashback nightmares) but I do like to know that my historical detail holds water.