Re: Fireformed vs Virgin Brass Accuracy
This post is geared mostly towards factory rifles due to the larger chamber dimensions.
Depending on how large your chamber is cut and how much larger your FF cases are versus factory specs, the volume changes a wee bit and does so enough to make pressure differences. This difference is enough to see a difference in accuracy equal powder charge for powder charge. Whether or not the accuracy change is better or worse is another story. Typically FF cases need a bit more powder to replicate the virgin brass. I dont know how much for a 7mm but in my old 308 it was 0.5 grains to duplicate the accuracy AND velocity.
Accuracy potential with out any other factors and just based on a FF case versus virgin brass CAN be noticable. I say CAN because every rifle is different. Some rigs as well as some calibers are more picky than others. When I say noticable I dont meen that it will take a .75 MOA gun and turn her into a .25 MOA gun. You may see between .1 and .2 MOA increase AT BEST in most cases. You can only see an accuracy increase IF your loading tequniques are such to take advantage of the FF case. When a case is FF, it leaves a case with the least amount of runout, provided your chamber is cut concentric. With this minimal run out, accuracy will increase. The key is to find a way to resize your brass without adding any mentionable run out.
Also if not done properly, FF cases can do the opposite. That is hurt accuracy. After each firing, the shoulder should be bumped back less than .001" to .001". If your chamber is oversized a custom die may be the ticket so you can bump the shoulder back a wee bit and not size the rest of the body too much either. A factory die will press everything back even though you can set it to just bump the shoulder.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.