If you will notice most if not all loading data for any round based on the 220 Russian case is based on a Sako or Norma case, can't remember right off hand, but think it is the Sako. Whichever, it is a weaker case than the Lapua case and therefore the maximum pressures are lower. More in the range of 48,000 to 54,000 psi., not CUP. Which is a different animal. I am quite sure some BR shooters are probably running over 65,000 psi on a regular basis. Some I would bet are bumping 70,000 psi. I certainly don't recommend this but I am quite sure it is being done with no problems. However these people watch their head space and case condition very close. The Lapua case is probably the strongest case made, except possibly for some military cases. As a side note several factory rounds like the 270 Winchester operate at 65,000 psi. I think the 243 Winchester is listed at something like 63,000 psi. So high operating pressures are nothing new. What you can run into problems with is rechambering some of the actions designed for lower pressure rounds to a round that normally operates at the higher pressures. The Cooper should stand the pressures with no problems if it has the smaller diameter firing pin. Hope this helps.
Donald
