I'll cover what happens when the round's chambered. The following is based on my observations, tests and measurements (OTM's). If your OTM's differ from mine, please post and explain them.
Oh, and yes, USSR, that's me.
But first, note that there's no such thing as a perfectly round chamber or fired case. They are all out of round by a thousandth or so, cases more so than chambers. If you have good tools to measure out of round (dial indicators on V blocks for cases and star gages for chambers, not outside micrometers nor hole mics) you can see what they really are. So there's no such thing as a "perfect fit" between case and chamber.
And second, fired cases from bolt action rifles are always smaller in outside dimensions than the chamber they were fired in. Not much smaller, but a thousandth or two is about all for max, safe loads. I've measured proof loads (blue pills) and they're smaller, too, but not as much.
Once the bolt's closed on a rimless bottle neck round, the bolt's extractor pushes the back of the case off center opposite the extractor's place on the bolt head. The back of the case doesn't rest on the chamber bottom but instead gets pushed against the chamber wall at the case pressure ring's location. Mauser style claw extractors push the case straight to the side. Sliding ones in the bolt face, such as the post-'64 Model 70's, push the case up. You can easily see where your bolt's extractor pushes the back of a chambered round.
Spring loaded plunger ejectors in bolt faces push the round forward until its shoulder centers in the chamber shoulder. So the front of the case body is typically clear of the bottom of the chamber. Centering the case shoulder in the chamber shoulder also centers the case neck in the chamber neck with a couple thousandths clearance around it. Even partial neck sized cases have clearance; go measure the chamber neck and case neck diameters and you'll see how much there is. If the action has a Mauser style ejector external from the bolt, it won't touch the case at all and the round could be anywhere between the bolt face and chamber shoulder, but it's back end is still pressed off center by the extractor and contacts the chamber wall opposite the extractor.
Depending on where the egg-shaped case fits the egg-shaped chamber, the clearance around the case will vary. Full-length sized cases will have a few thousandths more clearance than neck-only sized ones. If the bolt face has been squared with the chamber axis, it will have about the same clearance all around the fairly square case head; if not squared, the clearance will vary depending on how the round's oriented in the chamber and how much out of square the case head and bolt face is..
So here the chambered round fits; back end's against the chamber wall at the case pressure ring. The front's centered in the chamber at the shoulder if pushed there by the in-line ejector or just sitting there a bit below center if an external ejector's used.
Now the trigger sear releases the firing pin and it headed for the primer. It'll travel a fourth to a third of an inch in a few thousandths of a second and strike the primer with 25 to 30 pounds of force. Rimless bottle neck round such as the .30-06 weigh about 1 ounce.
My next post will explain what happens when the firing pin smacks the primer. If you well understand what's above, you can probably figure this out yourselves.