I have been trying to work up a load for my .264 Win Mag in a new Remington Sendero II. I had tried a number of loads and kept getting cratered primers no matter what load I was using. This if usually the first sign of too much pressure. Yesterday I went out to again try to find a good working load for this gun and was using Retumbo powder with the 140 grain MK. I started with the 61 grain load from my buddies book that showed right at max for Retumbo. Again even with this load I was getting cratering right from the get go and this kind of torqued me off a bit as it is a light load. I looked the cases over carefully and could find no sign's of pressure on the case and had absolutely no problem with bolt lift and very little recoil. Groups were about 5"s. Felt like a .243 on the felt recoil. But I had severely cratered primer pockets. The whole thing kind of threw me but I after considering everything else decided to proceed with my load work up. What I had intended to do was work up from 61 grains in 1/2 grain increments with 5 shots each until I was getting any signs of heavy bolt lift and then back off about 1 to 1.5 grains. As I proceeded up I noticed that my groups were starting to tighten up but with no problems with bolt lift I kept going. The cratering was still there but that was it. The cratering never got any worse, but was as bad on the first shot as it was on my last shot. I stopped going up at 68 grains and still did not show any signs of pressure. No heavy bolt lift was ever experienced. No real signs of case stretch and not really any signs of pressure. At 68 grains I had finally found a load that would shoot though and it was just under 1/2". That was as high as I had set up my groups of loads for and so I quit for the day. I did notice one other thing though that made me wonder though. Starting at the lower loadings I was getting sever soot on the outside of the neck. As the loads went up it became less about 67.5 and at 68 it looked about normal and at that point the groups had finally shrunk to under 1/2". All cases were Nosler custom brass, Federal 215M primers. Primers still severely cratered but everything else looked fine. No flattening just sever cratering. Here is the rub on the whole thing. When I went to clean the barrel it cleaned up nicely. The bolt face had some slight washes of brass on it but no ejector marks on the cases of any kind. All looked normal. But what really threw me though was size of the firing pin hole. Its huge. To make sure I pulled out 4 other Remington's from the safe and have something to check against and the hole appeared so be 25% larger in diameter than the others of which two are custom built rifles. I'm thinking that the whole problem with the primers is from an over sized firing pin hole. I measured as best I could as I really do not have a mic and only my digital case length gauge but the smaller bolt holes appear to be .070 and the one on the .264 appears to be .090. The protruding crater also measures about .090. Looks to me to be a faulty firing pin hole causing the whole problem rather than too much pressure. My thoughts on the matter are leave things as they are for now, go ahead and use it to hunt with and then after my upcoming hunt go ahead and have it bushed. The cratering is about .010 back into the bolt face.