They can, if they're hungry enough. Is yours a tiger pistol? That's what I have and they can get a decent size. When I first got mine, I saw him pull a couple of snails that were walking (?) by into his burrow. And I would see cerith snail shells that he had used to shore up his burrow walls. Now that he gets fed every day, he has kinda chilled out in that respect. Guess it just took him a while I realize he'll get food every day and doesn't need to kill anything to eat.
And you're gonna have hermit and snails die periodically too, it happens.
To help prevent this stuff, when you feed the tank, use a turkey Baster and put some food into one of the burrow openings. And the pistol will need shell frags to shore up his walls. So place a bunch near a opening of the burrow. He'll drag them in and use them. If you don't give him any, he'll probably kill hermits and snails to get his building materials. It's in his nature to build. I had some shell frags from the beach, boiled them, let em cool and put them right by the main opening. Usually LFS will sell snail shells and frags for cheap if you don't have any. I have to ask at my LFS cuz they keep the box of shells behind the counter. I've put at least 30 shell frags in The tank over the last 5 months or so, and he's used them all.
Enjoy your new addition. He's super cool to watch!!