I think this has all been covered by the other guys already. But just to kind of lay it out in order.
There may be a problem with your press. I'm not going to discount that as a possibility. But it's probably the least likely possibility.
If, you are getting a hard cam over, shell holder against the bottom of the sizing die on every case, and getting head space variation - it's not your press. I believe the Summit is a C press? Nothing really wrong with a C press, but they aren't as strong as an O press like a Rockchucker. And by strong I don't mean leverage. I mean resistant to "springing". Or deformation or "opening up" of the press frame under heavy load. If you are getting hard cam over, shell holder against bottom of the die, steel against steel as Erich put it, that springing doesn't make any real difference. Even if the press frame "opens up" a bit under heavy pressure, the final sizing parameters are set in stone by that steel against steel cam over.
You mentioned slop. Hard cam over takes all the slop out completely.
So, if, you are getting hard cam over, steel against steel. Your head space variation is either a variability in the hardness of your brass, or a variability in how well lubed each case is. That simple. One of the two. Or, I guess it could even be a combination of the two.
But, if, you have some space between your shell holder and the bottom of the die at the top of the stroke - which in many bolt rifle applications is not uncommon. Then, press "springing", or opening up under heavy pressure could be at play. And that is a real thing even with O frame presses but much more so with C frame presses. But, it would still be related to brass hardness variability or lube variability. If all the brass is of equal hardness and equally lubed, that springing will be consistent from case to case and again, won't make any difference. At the same time, getting the shell holder camming over hard against the bottom of the die removes the springing variable altogether.
So, if you aren't hard camming, steel against steel already - I would. As Erich pointed out, if that is a problem for headspace, Redding Competition shell holders are the easy button answer to that. They allow longer headspace in .002 increments while still maintaining steel against steel rock solid consistency of brass depth into the sizing die.
If you are hard camming already, brass hardness variation - anneal. Or lube inconsistency, change up your case lube protocol. Possibly a combination of both.
Or, there might actually be a problem with your press. It's the least likely, but possible.
- DAA
