Back up to where the primer has lit off some of the powder, the gases are expanding, the pressure increases, the case swells and the neck opens. If the bullet is seated hard into the leade, then the pressure is going to rise until it starts moving. Is the pressure moving only forward against the bullet base? Of course not. It's going towards an area of lower pressure in a period measured in nano senconds I suppose. The pressure seeks an escape, so to speak, and the only place for it to go once the case has expanded fully is in between the bullets foresection (whatever shape that may be) and the grooves. Is there any lube for the pressure to carry with it there? No. So are we to believe that the gas, burning from the rear is moving in a linear direction or are we to believe the pressure rises more or less equally within the case? Until there is a area of lower pressure for the gases to occupy, (the grooves), the gases are busy swelling the case out, shoving the case back and so on. As the bullet starts to move the first part of the bullet to fill the groove seals that escape area. (Is there a reverse pressure wave created at that point?) The gases are not moving in a linear fashion along the sides of the bullet, at least not in my imagination. The gases are piled up against the throat area and all of it is trying to get into the groove space. There is only a tiny area for the rushing gases to accelerate to any degree and that's in between the nose and front of the first drive band. If there was lube there, then yes, I could see some being carried into the barrel ahead of the bullets first drive band or even, perhaps, the nose. If there isn't, where is the lube supposed to come from? If the bullet isn't hard seated, if the nose has to go a ways before it starts to engrave and seal, then my imaginary movie of this happening is still not seeing linear gas pressure back at the lube grooves, but up in front of the nose. Yes there is a pressure wall that moved as the intial powder started burning, but that wall (I picture a storm front) is relatively low pressure as it first moves across the body of the bullet as the case starts swelling and the neck opens. If anything, I would think the pressure is going to rapidly fall in the tiny time period as the neck opens, the lube in it's grooves starts to compress into any space available and the front of the pressure wave moves to the bore. Of course more powder is burning and pressure increasing, so maybe it's a wash in that respect. Once the bullet is moving and gets into the throat and leade, conventional wisdom says it sort of stops or slows at least and the pressure builds at a different rate until the bullet regains it's movement. Again, the pressure builds more or less equally, we have to say "more or less" because we can't measure inside the case, and the only place for it to move to is that area between the groove and first drive band. I can visualize a tiny bit of lube being thrown forward from the relatively sudden slowing of the bullet, but we're into that time/pressure/distance area again. Is there actually time for any lube to move in the period? I dunno. Is the lube capable of moving under the ambient pressure? I dunno. Once the first drive band is in the groove, given anything like decent fit and smooth barrel, we shouldn't have much, if any, escaping gases. At least that's what we aim for. So I'm back to how, when and where could any significant amount of lube get ahead of the bullet that is came from?
Let me say this- What I lay out is how I picture it. I believe, and I have no more proof than anyone else, that most of the lube that is deposited in our barrels gets there in the throat and first few inches of the barrel when the bullet has the most chance of being "plastic" and that some lube is forced against the barrel walls as the bullet compresses. I also think some is thrown against the barrel walls from acceleration. I think, again with no real proof, that a good deal of the lube that is lost off the bullet occurs as is exits the muzzle and the following gasses do have a chance to rush by as the bullet starts to slow. Some may be lost as the bullet spins it way to the target. It's all conjecture as I imagine things progressing. I won't ever put it in terms of "This is what happens..." because it's just a theory. Sometimes things are said that don't make sense to me. I tend to obsess a little I suppose, but as I said, it sure beats trying to figure women out.
There ya go. Worth every penny you paid for it. No disrespect to anyone, anywhere intended.