I recently got some Barnes 400g Originals for my .45-70 Govt in my NEF. I loaded up 3 at 45g IMR-4198 and shot them at 100 yards. After the 1st shot I inspected the case as I usualy do with all reloads. I noticed something what I think is unusual. Above the rim, about 1/4" it feels like one side of the case is bulging out. This happened to all 3 cases. THe 3 shot group was stopped after 2 shots were 6" apart, the 3rd was shot at a boulder, that was pretty fun. Other then that, the primers weren't flattened or sooty or anything, or further indicating high pressure. What do you guys think?? This load is not even a MAX load according to Hodgon website under the lever-action loads. About 2g less I believe. I
Sounds to me like you are over pressure for you action. The NEF's are not in the pressure range of a Ruger#1. With those Barns bullets you need to back off quite a bit on the powder from what you would use with a cup and core bullet. The NEF action may be flexing open a bit by too much pressure and causing the bulge on one side of your case. With the 45-70 you don't need a great deal of velocity to have a real killer on game. A 400 to 500 gr bullet at 1100 to 1300 fps will shoot through about any critter walking this earth. I shoot a lot of black powder loads in my Sharps 45-70. I once shot a deer at 110 yards that was look strait at me with 70 grs. FFG under a Lyman 420 gr. #457193 FN Cast bullet. I was aiming at the white patch on it's chest but the deer must have put it's head down between the time I fired and the bullet got there. The bullet struck the deer right between the eyes traveled down its neck making saw dust of its spine, broke the left front shoulder and exited behind the shoulder and went down and shot its left back leg completely off just above the knee. Then the bullet hit the hard pack ground of the logging road the deer was standing in and went down it for about 15 yards looking like a mole track then came out of the ground and went through a 4 inch tree and then kept going because I never found it. This bullet was only going about 1300 fps or so.
It sounds like the chamber was cut a little big to me. Its simply to much pressure for a loose chamber. The main concern for the 45-70 case would be the thickness of the web in the case head. The thicker the web the more pressure it can handle. Case walls bulging is simply the amount of space that the case has to expand into. A tight chamber would allow you to run up to the max pressure the web can handle, before the brass starts to extrude into the little creavases in the bolt head, in the appropriate action of course.