It's time to set up a resizing die on your reloading press. You screw the die down and pull the handle, but at the top of the stroke the press pops. The handle slips a hair past center. Should the press do that? Has your sizing accuracy been affected?
The short answer is yes, your press is designed to go through this adjustment, called a cam over. In general, for almost all resizing, RCBS recommends you cam the press over. Here's what cam over is and why it matters to your reloading process.
Why Cam Over for Reloading?
A reloading press has moving parts, and all moving parts in any machine have some amount of slop or play. On a bargain basement press, our trusted Rock Chucker, or even a high end $1,500 boutique press, there will be some level of play within the different parts of the press. Pins sit in holes, and the holes are a touch bigger than the pins. All that play adds up at the top of the stroke.
Camming over squeezes this play out. As you push your shell holder into your die, the resistance you feel is normal and will not hurt the press. This simply removes the play from the press linkage and nothing more.
Why bother? Camming over produces repeatable sameness and consistency. Every case rides to the same depth into the die. Every case comes out the same on a consistent resize.
Camming over is not a way to size your case to a different dimension. Want more shoulder bump? Move the die down and measure. Camming over just locks in the setting you picked.
How to Cam Your Press Over Properly
Bring the shell holder up
With the handle down and the ram raised, the shell holder sits at the top of the stroke. Screw the sizing die down into the top of your press until it touches the shell holder.
Go another 1/8 to 1/4 turn
Lower the shell holder by raising your handle, then screw the die down a little more, about 1/8 to 1/4 of a turn.
Feel for the pop
Pull the handle again. You'll feel a slight thump as the leverage system cams over center. The press will pop as the linkage cams over, and that means your cam is set up correctly and, most importantly, repeatably with each case you resize.
How Far Is 1/8 to 1/4 Turn?
That fraction sounds vague until you do the math. On a standard 7/8"-14 die thread, a full turn moves the die body about .0714 inches, so a quarter turn drops it about .018 inches and an eighth turn about .009 inches. That small range shows the level of precision we're going for. As you set up more dies, you'll get a feel for exactly where this adjustment needs to be.
| Die Adjustment | Die Body Travel |
|---|---|
| 1/8 turn | About .009" |
| 1/4 turn | About .018" |
| Full turn | About .0714" |
Is a sized case still a bit tight in your rifle? Go down another 1/4 turn. Once the brass chambers with ease, lock the die ring.
Case Lube
Not all of the resistance comes from the linkage and the press. Some of it is the brass. To keep from sticking a case, always lube the bottom two thirds of the brass for full length sizing. Our guide on how to prep your cases for sizing walks through pad, spray, and lube die methods.
The Exception: Do Not Cam Over Carbide Dies
While camming over is a reliable process for rifle dies, on the carbide sizer dies commonly used with pistol cartridges you do not want to cam over. That extra travel can affect the carbide ring inside your sizing die.
Screw the die into your press until it contacts the shell holder only, and leave it there. No extra adjustment required. This protects the polished carbide ring insert inside the die. Carbide is a hard material and can be chipped.
Some reloaders take this a step farther and leave a 1/16 inch gap between their shell holder and die when resizing with carbide dies.
Seater Die Set Up
A seater die is a different animal than a sizing die, and with this die no cam over is required. The seater die's job is bullet depth, not case size. Screw it all the way down and you may crimp by mistake.
To set up a seating die, screw it in until you feel it touch the case mouth. Then back the die up one full turn and set the lock ring. You can set and adjust your depth with the seater plug after that.
Set It and Check It
- Bottleneck rifle sizer die. Contact, then 1/8 to 1/4 turn more. Feel the cam over.
- Carbide pistol sizer die. Contact only, or a 1/16 inch gap. No cam over.
- Seater die. Touch the case mouth, then back up one full turn.
- Every die. Lock the ring once the setting is right.
- Before you load. Size a few cases and try each one in your rifle.
To check your work, always chamber the resized case before priming, adding powder, or seating a bullet. A sized case that drops in easy tells you the die is right. You can also check your resized case dimensions for correct case length against your reloading data.
Set your dies with confidence
Rifle die sets, carbide pistol sets, presses and case lube, all in stock.
Always follow safe reloading practices. Consult current published load data and your equipment's instruction manuals before beginning any reloading operation.
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