THIS COULD BE THE BEST FORUM EVER... but it's not. Including some info related to muzzleloader nipples and sizes. Best-

Nipple Size Comparison

Thread Sizes:

• 1/4-28: Common in many modern American-made muzzleloaders for #11 percussion caps. This thread size is generally found on rifles like those from CVA (pre-2003 models), Lyman, and Traditions for certain models.

• M6x1 (6-1mm): A metric thread size often seen in European and some American reproductions, especially those from Italy or made for Italian designs. This is noted for compatibility with certain Investarm, CVA (post-2003), and other Italian replicas.

• M6x0.75 (6-0.75mm): Used in some Italian-made firearms, like the Lyman Great Plains Rifle & Pistol, and other similar models.

• 6x3/4: Specifically noted for Pietta black powder revolvers, indicating a unique metric thread size for specific revolver models.

Flash Hole Diameters:

• 0.028" - 0.031": Commonly recommended for modern black powder rifles using #11 percussion caps when shooting bullets, to optimize ignition without excessive blowback.

• 0.032" - 0.034": Some users have reported these sizes, with larger diameters potentially leading to hammer blowback or reduced accuracy due to excessive gas escape.

• Variable: Older or bespoke nipples might have significantly larger flash holes, historically up to 1/16" or more, due to different cap sizes or the desire for more reliable ignition in early percussion firearms.

General Notes:

• Standardization: There isn't a strict industry standard for nipple dimensions; manufacturers can have their own specifications, leading to variations even within the same thread size.

• Caps Compatibility: The size and design of percussion caps can vary, affecting which nipple size works best. For instance, #11 caps are standard, but the exact fit can differ slightly between manufacturers.

• Material and Design: Nipples can be made from different materials (stainless steel being common for durability) and may feature different designs like Hot Shot or Spitfire for enhanced ignition with black powder substitutes.