Magnum Primers for AR loads

[sinister]

Military ammunition uses magnum primers to ensure complete and consistent ignition in cold temperatures. They also have thicker cups for pressure containment, while the entire primer is also staked into the primer pocket -- all precautions to prevent failure in automatic fire and in high-temperature climates.

Compare cup thickness between CCI 400s and 450s, Fed 200s and 205Ms, and Rem 6 1/2 and 7 1/2. The "Standard" cups are for rifles like M1 Carbine, while "Magnum" small rifle primers are for .223 and 5.56 through .22 Hornet and 22-250.

[HKGuns]

Thanks Sinister, that is great information that I've not seen before, or don't remember and I've been reloading for over 20 years.

[MarshallDodge]

N140 has shot very well for me under the 77 SMK. Even with blems, I was getting well under MOA out of the bolt gun with a 223 chamber.

77 SMK, 24.0 N140, LC brass, Federal 205, 2.270 OAL.

I would move to a CCI450 if I bumped up the charge. With a 24" barrel, there isn't a need to push them hard.