I'm going to jump to the conclusion that your bullets are wiggling in the neck.
Basically, two possible areas of fault here :
1. Your resize die is making your case neck too large.
Solution : Measure a factory loaded piece of ammunition, or unloaded piece of virgin brass and compare it to what your die sizes for you. If your case is bigger than spec- thats your issue. You will either need to have your sizing die re-milled completely, modified for fitment, or purchase another depending on the specific malady. If you aren't a machinist- leave it to a pro and save yourself a lot of headache if this is the issue.
2. Your bullets are too small. .300 savage still fires a .308 diameter bullet, as the winchester .308 was an offspring of that chambering.
Nominally, a jacket .308 round comes out to .309 from most manufacturers.
A cast lead round could easily ( and most commonly) be cast anywhere from .309 to .310- .310 being often sought in cast lead bullets to help seal the bore- or for other reasons I'm sure someone will be along soon to offer an opinion on. I personally load .311 cast bullets which work just great in my lever action .30-30- also designed for a nominal .308 bullet.
Solution : Nevertheless, if your bullet is less than .309 by measuring it with calipers, and your die is shaping your brass correctly- that would be your issue- your bullet is too small. Find a proper sized bullet.
Theoretically it would be possible to have both at the same time....however that would most likely result in a gap so large you could simply push the bullet completely into the brass with just the pressure of your fingers....if it just didn't fall through of its own accord.
Your bullets; did you cast them yourself? Or purchase them from a a store or over the internet ?
If you cast them yourself- there are a whole list of things that could be at fault, but I will wait for your reply.
