Powder granulation importance?

[JCKelly]

In any "modern" barrel there is almost zero risk if you use a reasonable amount of powder,
Modern American muzzle loading barrels are mostly made of screw stock, AISI 12L14. This grade has sulfur phosphorus and lead added, so it can be machined at very high speeds, making nice short crumbly chips. 12L14 bar is meant to be machined in a collet, not a chuck. This requires finer tolerances - rounder bar - than can be made by just hot rolling that bar. So, the hot rolled 12L14bar is cold drawn to make it round with fine tolerances. In the process of cold drawing this grade has been known to crack.
Does your barrel maker test his 12L14 bar for cracks?
How do you inspect the barrel?

 

[Throwdown58]

Right now the advice I'm giving people is to use whatever you can get. I ran into a goldmine of 2F TripleSe7en at Bass pro and scarfed several, and will happily shoot them in my pistols, with no detriment whatsoever in my experience. I was just loading paper cartridges with Pyrodex RS in fact. It's the same for BP. As many people above have said, pet loads in rifles are often 3F, and 1 and 1.5F. And in pistols 2F, 4F, I've heard it all over the years.

 

[Dashing Leper]

Historical revolver cartridges have been taken apart and the powder is consistent with 4fg.

Decades of thermal cycling are bound to break granules down and create a finer powder within the cartridge as a result. Black powder rocket motors have a prescribed shelf/service life because the cycle of day/night heating/cooling eventually creates cracks that promote faster burning of the charge.

If every single granule of 3Fg eventually broke up in a charge, you'd get 4Fg.

 

[Britsmoothy]

Decades of thermal cycling are bound to break granules down and create a finer powder within the cartridge as a result. Black powder rocket motors have a prescribed shelf/service life because the cycle of day/night heating/cooling eventually creates cracks that promote faster burning of the charge.

If every single granule of 3Fg eventually broke up in a charge, you'd get 4Fg.

So how come old cans ain't turned to dust?
And how long does the chain last on a thermal cycle rocket?