Which of the following is an unsafe practice when using a muzzleloader?

Loading directly from a horn or flask is considered an unsafe practice when using a muzzleloader because it can lead to an accidental ignition of the powder. When you pour powder directly from a flask or horn into the muzzleloader's barrel, any static electricity or sparks can ignite the powder, potentially causing a serious accident. This method lacks the safety of measuring the charge in a controlled environment, which is critical in preventing mishaps.

In contrast, loading one charge at a time allows for more controlled handling and reduces the risk of multiple charges being ignited simultaneously. Using standard black powder is common practice among muzzleloader users and is generally safe when handled properly. Employing a patch and ball is a standard and safe method for loading a muzzleloader, designed to ensure the projectile remains securely in place while providing a good seal for the powder charge.

Therefore, it's essential to avoid loading directly from a horn or flask, as it increases the risk of accidental ignition and mishaps during the loading process.