Your gun will be marked with the bullet weight it was sighted for, most likely 13 gram. I've had a few sighted for 15 gram Bullets. I have a modern 20/20/8X57IRS Merkel sighted for 13 gram (200 grain) Bullets, but I got a bargain on 25 boxes of 180 grain Hornady export ammo and re-zeroed for that. Superb caliber. There's nothing wrong with S&B 13 gram ammo.