Originally Posted by blipelt
Sorry but I am a little confused. I just got my 280AI from Cooper firearms. It is chambered in the original AI chambering supposedly from what they tell me. I got a 40degree RCBS dieset that was rec. by them. I bought Nosler custom brass also. Everyone is saying Nosler is sammi spec. But the brass chambers in my Cooper without any resistance from the factory? Is the sammi spec longer or shorter, I thought it was longer? I plan on creating a false shoulder and fireforming the brass much like I do with my Dasher. If I find any discrepencies with the brass.
This has been discussed a bit lately but the only physical evidence I can find is Woods flattened primers. Iv been using nosler brass in a cooper chamber 280ai for years with no problems at all( zero stretch in case length).
The opposing theory to to different chamber lengths is that the chambers are the same but the datum at which they are measured is different.
To answer the question for myself I have some original ackley go gauges and new nosler brass coming. I plan to check the chamber, the new brass dimensions and then the fully fire formed dimensions.