If one chooses to neck size as much as possible (like I do), the solution to possible chambering issues is to test feed and chamber every round of handloaded ammo (observing all safety rules, of course) before you take them out into the field. If they don't feed well, then one has the opportunity to correct the situation before a once-in-a-lifetime opportunity is ruined because one couldn't get the bolt closed.

As for the original question, I can honestly say that I don't know, but would be very curious to find out. I almost exclusively neck-size my rifle cases. I only full length resize when necessary, and even them only enough to bump the shoulders back just enough to allow the cases to chamber easily. The few times I have FL sized I really never gave much thought to the effects FL sizing would have to velocity. This would be a very interesting question to follow up on with a little experimentation involving a chronograph and identical load workups using both FL and fireformed neck-sized brass.

When the weather gets a little warmer and I get around to sending my chronograph in to be fixed, I might just do a little experimenting to see if there really is any difference.

Mike