[Lambo]

I have some .223/5.56x45mm Cases that I've re- sized/decapped & milled the pocket to remove any crimping. I attempted to prime them using the CCI SR BRs and they wouldn't seat, they seem to be larger then the pocket.
The markings are LC 06 which I believe is Lake City/Manufactured in 2006? Is there a special primer used for this lot?

[dcloco]

You will have to remove the crimp completely. It is better to swage the crimp, then cut it.

You just have not cut deep enough yet.

[Linear Thinker]

Lake City is correct - it's USGI brass, with crimped primers - you need to swage or ream the crimp off.

One thing to keep in mind with military brass - they are thick-walled, and have reduced powder capacity. The usual rule of "start 10% below listed powder charge" needs to be adhered to, I would even go 12% below.
LT

[ADKWOODSMAN]

You can remove the military crimp by using your case neck deburing tool and run it around the primer pocket edge. You may have to do it a second time until the mil crimp is gone.