How do I select the core seating punch diameter?

[rossi]

Up to now I have swaged mainly .224 bullets, using .22RF cases as jackets or commercial jackets. I own two core seating punches. One is “large”  and the other has a smaller diameter. The larger fits the .22Rf jackets nicely, while the thinner punch is ok for commercial jackets with a thicker wall (compared to RF cases).
I have bought a core seat die and punch from D. Corbin and some of his .308 VB jackets. I have asked for a core seating punch with proper diameter to fit his jackets. He sent me a punch that is .277 in diameter. The punch is larger than the jackets he sent me. I am not able to insert the punch into the jacket by hand without exerting considerable force, and once the punch slightly enters the jacket I have to use a pair of pliers to remove the punch by hand. On my first seating attempts the jackets stuck onto the punch. I wrote to Corbin describing my problem and he told me that the punch has to be slightly larger than the inside diameter of the jacket in order to develop the necessary pressure on the core, allowing the jacket to expand properly. I tried to seat the cores “harder” and the seating punch left the jackets with the seated core without effort.

Now I have one big question!!!

Should the core seating punch always be slightly larger than the inside diameter of the jacket??

On my .224 bullets I seat the core using a slightly smaller punch than the inside diameter of the jacket. If I seat the core too hard, lead flows around the punch and the jacket does not come of the punch. I adjust the seating die so far until I can see a slight lead ring inside the jacket, and measure the final diameter of the jacket to see if it had expanded properly. Is this procedure wrong? Should I buy a larger seating punch?
Having a punch larger than the inside diameter of the jackets does not allow any lead to flow around the punch and the pressure on the core becomes a variable that can be influenced, while using a smaller punch allows only so much pressure until the lead starts to flow.
What is the correct choice concerning core seating punch diameter? ?
Any concerns about scraping the insides of the jacket when using a larger punch?

[Rick Teal]

Contact Dave Corbin and let him know.  The core seating punch should be a little under the starting ID of your jackets.  I'm not familiar with the VB jacket, If its tapered inside it may be necessary to have more than one seating punch.  I would expect the friction of forcing an oversized punch into a jacket would cause unacceptable wear on the punch and would peel copper from the inside of the jacket.

I believe that conventional .30 cal. jackets have a starting OD of about .304.  If they have a wall thickness of .015, the ID would be .274.  I would guess something like a .270 (or so) punch would be appropriate.

When I switched from .035 tubing jackets to .030 commercial jackets for my .358s I noticed some lead running up beside the punch head, and I probably should have ordered a slightly larger punch, however, this lead run up never caused my punch to stick inside the jacket.  The only times I've had jackets stick on the punch head is when I didn't apply enough pressure to fully expand the jacket.  When the pressure was proper, friction inside the die would the seated jacket in place allowing the seating punch to be withdrawn.

[GREYGHOSTt]

for thin skinned jackets .0005 larger than the inside diameter usualy works fine, the flow by can cause jacket cutting. a very small chamfer on the edge of the punch prevents jacket shaving.