My thinking alsoI'd agree that it was either a blocked flash hole or bad primer. What primer was used?
Do You wet tumble?
Spray case lube used to size brass?It appears some type of reaction in the powder happened.
I have Peterson brass in 6XC, .260 Rem, .280 AI and 6.5 PRC. I never had a problem with new brass (over 1,500 cases) after running them through a FL sizing die, loading and shooting. What sort of contaminant did you find? To repeat, I've never experienced a FTF with new Peterson brass.Have only had it happen in new Peterson brass. Any loaded right from the box, had FF or hang fires. The FF were disassembled and clumped powder was evidenced. Removing the primers showed they had fired and powder failed to ignite.
Brass was 6 mm Creedmore, 223, and 6mm BR.
This is where I would start. Something contaminated that powder or the powder is starting to degrade. Clumping and sticking together are indications of some kind of possibly serious problem . Maybe excess lube inside the case neck? Put on your investigation gear and go to it. Good luck and keep us posted.Signs of contamination in smokeless powder
Reddish tinge/rust like color
Foul odor
Clumping
Loss of smell
Changing from gray to brown or white.
Contaminates: Nitric gas, copper, nitrite, residue of incomplete burn,acetic acid, alpha-naphthol, nitrates.