I'm new to reloading so I don't know if this is normal or not. I'm reloading for a 308 using new win. brass sized using a forester bench rest die and 175gr smk bullet. When I seat my bullet I notice that a small amount of the jacket is shaved off. I would think that it would be bad for accuracy.
Yes, indeed it is. You may not notice it at short range, but long range that will sure show up. Are you chamfering your case mouths prior to seating the bullet? Shaving jacket material usually indicates either way too much case neck tension, or not chamfering mouths adequately. I've switched to a VLD-style chamfer tool. It has a sharper angle to it, so it eases those bullets in better, and less likely to damage the jacket.
I'm using the RCBS chamfer/ deburring to. I actually noticed more consistant bullet damage after using it. I will try the VLD chamfer and see how that works. When using these tools how much effort do you put into it?
Doesn't take much. I just run about 1.5-2 revolutions of the tool, and that seems to work well for me. Mine's a Lyman, but RCBS, Sinclair, and others make them as well.
I had one set of dies that oversized the neck excessively, and put too much neck tension (pull) on the bullet. Even w/ chamfering those cases sized in that die would shave jacket material off. Switched to a new die, and problem went away...
I just resized some 300 WM cases through 2 different sets of dies. Both resized the necks to about .306", so similar to yours. Where I'm seeing the difference, though, is in my bullet diameters. I just measured 30 caliber bullets from Hornady, Nosler, Swift, and Sierra (GK, didn't have any 30 cal MK around), and all four brands run at or just barely over 0.307" - if your SMKs are measuring 0.309", I would guess that's what's causing it....
I tried the vld tool but felt I wasn't as consistent with it as I am with the normal chamfer tool. Meaning I would cut some deeper than others.
In my opinion the key to not shaving your bullet jackets is not to limit yourself in regards to bullet tension but rather eliminate the edge which has the potential to shave. No matter which design of chamfer cutter you choose to use.
Using a normal chamfer tool leaves the edge up near the top of the case mouth. Then you can break the sharp edges by twisting the mouth into a wad of 0000 steel wool until it feels smooth. A couple of twists is all it takes.
If I have a bunch to do, I will use a drill and a small nut driver bit that has a small magnet in the middle to hold screws. I stuff a wad of of the steel wool in the end and commence to polishing all of the case mouth chamfers very quickly.
I use alot of tension on some of my rounds. To a degree that pulled bullets have a uniform sheen on them that looks like a resized case. But they are not scarred or dug in any way.
And you will notice a great improvement in bullet seating.