You originally said,
Does FL sizing and not bumping the shoulders back far enough (there is still a very hard bolt close and lift) affect pressure/accuracy?
then you said,
According to a shoulder gauge, it's actually getting bumped back 2 thousands. For some reason its just not enough. I would have to hit the bolt down pretty hard a few times with my Palm, just to get it to close. I had to bump it back a full 4 or 5 thousands until there was little resistance.
so I'm confused by two things.
1. if you are full length sizing but not bumping the shoulder, why does the shoulder gauge show a .002 reduction?
2. if you have to pound the bolt down, something is binding on something else.
a. The case base to shoulder length is too long. When the bolt pushes the case as far as it will go, the locking logs on the bolt just miss fitting over the lugs on the front of the receiver. You have to hammer on the bolt handle to force the bolt lugs up the receiver lugs and shorten the case in the process.
b. The case body is too large. When you close the bolt, the case base jams into the back of the chamber. You have to hammer on the bolt because that forces the case more deeply into the chamber and forcing the case body to be smaller.
c. There is dirt somewhere interfering with the bolt lug to chamber lug movement.
d. The neck is really tight. You really don't want this.
e. The rim is expanded and you are having a hard time forcing the brass into the bolt face. If you have trouble fitting the brass into your shell holder, measure the rims.
Here is a suggestion:
Find a tight case, one where you have to push hard on the bolt. Magic marker the case base, body, shoulder, and neck. Chamber it a couple of times. Look to see where the marker is rubbed off. That is the dimension that is wrong -- unless! the base is the place where the marker rubbed off. That means that the case was jammed into the chamber and the pounding is to rotate the bolt over around the base. In that situation, you will have to do the sizing the bumps the shoulder back .002 and repeat.
I used to shoot my 300 win mag brass this way. Then I stopped for a couple of reasons, one practical and one tactical. First the practical. I suspect that the issue is this: the brass is chamber length or a little longer. For the cases that are chamber length, you can close the bolt but it is tight. For the cases that are longer, you have to force the bolt. How did they get longer? When that weapon fires, there is about 55,000 psi in that case. For a 300 win mag case, the case base diameter is about .532. using pi * r**2, the area of the base in about .41 sq inches. Apply 55,000 psi to that area and you get over 20,000 pounds. That force is enough to stretch the chamber a little and the brass expands to fill the space. After the shot, the brass is compressed. When you open the bolt, the case springs back by a couple of thousandths. The next time you try to chamber it, the bolt doesn't want to close. In my opinion, you don't get any advantage from this. That is my opinion, you should do what you think is best.
Second is tactical. If I am fighting with that weapon - or even hunting - I may need to shoot rapidly. If I have trouble chambering a round, undesirable things could happen while I am looking at the gun and not at the target. I full length size almost everything. I bump shoulders between .001 and .002 off the chamber. The rounds feed smoothly and the bolt closes with just a hint of friction in the bottom one quarter of the stroke. I shoot out of a magazine. Other people may have better groups but I am happy with my setup.
