209 primers

Thought all 209 primers were created equally.

What is the difference between 209 primers for shotgun & 209 primers for muzzeloader?

I always thought a 209 was a 209, it's probably just a marketing ploy to relieve you of more money. I could be wrong, but my money's on the marketing gimmick.

Supposedly muzzleloader 209 primers have subtly different chemistry to reduce hard residue build-up with BP subs.

Waiting for an outside chemist to tell us for sure .

The 209 made for muzzleloaders are not as hot as standard shotgun primers and are designed to keep down 1)primer debris in the flash path and 2) cut down on the crud ring from some substitute BP products.

I have never found a difference in using standard shotgun primers vs muzzleloading primers. I have tried both Remington clean bore and the Winchester primers and all I found to be different is the price!

Following my posting and question, did a few google searches, was surprised to learn there is a difference. Many threads on the difference, but I like the following article:

https://namlhuntcom.fatcow.com/hmlhunter-blog/not-all-209-primers-are-created-equal

Some 410 primers were developed for a longer duration of flame to aid with the ignition of long powder columns in the hull.

These primers were also selected for muzzle loaders to aid in keeping an annular ring of carbon from developing in the breech to quickly.

Once the annular ring developed during extended course of fire the area of the breech that supported the powder column becomes extended.
Certain types of projectiles can be affected by the inconsistency the condition created. The inconsistency caused varying degrees of the force needed to firmly seat the ball (bullet) and physical damage to the projie base if it was constructed of 100% soft lead, pillow ticking patches or the skirt attached to power-belts. Consistent seating pressure probably the biggest contributing factor in MZ accuracy. Once the ring forms in a shot string you can feel the projie break past the crud when its being seated. Patch spitting and wiping between shots helps but is not always the same as a thorough cleaning. In lead based projies, once the part of the base becomes deformed the part of the base that is subject to obturation becomes inconsistent because of the mechanical damage.
This is where nylon or plastic based sabots came in because the are more reliable once the pressure of the charge blows and seals the hollow Minie' style base sealing the bore a little more consistently from shot to shot.
T/C in the early stages of modern MZ development attempted to address the problem by designing sabots that used a wad or buffer between the ball and powder column, (TC breakaway sabot) and the vented breech area of the scout design.
The latest designs offer different breech arrangements/designs to work better with the different propellants marketed for the modern muzzleloader which are to my knowledge more stable than BP but a little harder to ignite because of their stability.
Also the close tolerances encountered where a 209 primer seats at the rim and main body of the primer in the breech plug do not allow for much blow back to occur which could compound the problem but does allow for the primer to be easily removed.
Hammer blow back used to be an indication that maximum pressures have been reached in the particular arm but is rarely discussed these days because it doesn't occur in the modern designs with the exception of the occasionally hard to remove primer and the addition in some models of tip up extractors.