1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

What does it mean to "cam over"?

Discussion in 'Handloading and Reloading' started by uneasy_rider, Jan 26, 2008.

  1. uneasy_rider

    uneasy_rider Well-Known Member

    Thanks for the help.
  2. R.W.Dale

    R.W.Dale Well-Known Member

    Cam over is referring to the point of adjustment of your reloading dies in between where the shellholder touches the die body and where the handle/ram isn't able to bottom out.

    In the middle somewhere is a point when the shellholder will contact the die body Before the ram/handle reaches it's maximum travel YET is still able to be forced down the rest of the way against the die. AKA cammed over
  3. 30Cal

    30Cal Well-Known Member

    The linkage between the ram and the lever allows the ram to reach top dead center before the lever hits a stop. So when you throw the lever fully, the ram comes all the way up, then down just a hair. That's it. If you thread your dies down far enough, you'll prevent that from happening because the die will serve as a mechanical stop for the ram.
  4. uneasy_rider

    uneasy_rider Well-Known Member

    So if I screw a die in until it contacts the shellholder, and then screw it in a quarter turn more, will that prevent cam over?
  5. R.W.Dale

    R.W.Dale Well-Known Member

    Why would you want to prevent cam over? It's actually necessary in order to full length size cases.
  6. uneasy_rider

    uneasy_rider Well-Known Member

    The instructions for RCBS full length sizing dies say, in all capital letters, DO NOT CAM OVER.

    So that is why I was thinking that.

    How do you adjust the die so you cam over?

    How do you adjust the die to prevent cam over?

    What exactly does cam over do when full length sizing?
  7. R.W.Dale

    R.W.Dale Well-Known Member

    OK here's the deal

    I'm rather surprised RCBS states that. I don't recollect my RCBS dies saying anything of the sort. I'll have to do some more research

    On ANY reloading press no matter how sturdy it looks you can have an surprising amount of upward frame flex with hard to resize cases. What happens when you have a non cammed over press is even though the shellholder touches the die EMPTY when you add a hard to size case forcing the frame upwards you end up with a PARTIALLY resized case.

    This is no big deal when loading for bolt action rifles or straight walled pistol ammunition. But with other firearms like pump actions and straight pulls it can mean the difference in ammunition that will chamber and ammo that will not.

    Camming the press over brings all the mechanical parts of the press to "0" against the die body
  8. uneasy_rider

    uneasy_rider Well-Known Member

    So how do I need to set up my full length sizing die for correct sizing?

    The instructions say to screw the die in until it touches the shellholder, then lower the ram and screw it in an eigth to a quarter turn more. Then the instructions say DO NOT OVER CAM.

    Ok, so if I follow the instructions about, and screw the die in an eighth to a quarter turn more, will I or will I not over cam?

    How would I adjust the die to over cam??
  9. BigJakeJ1s

    BigJakeJ1s Well-Known Member

    Cam over is simply a feature of most reloading presses where, due to manufacturing tolerances, the top of stroke of the ram occurs before the mechanical stop on the lever. This ensures that the point of maximum leverage (by definition at top of stroke) is at least reached in order to ensure maximum force for resizing, no matter how the tolerances stack up. But not all presses cam over (Forster co-ax does not).

    Correct die adjustment, as well as ample press rigidity and leverage, not cam-over, are necessary and sufficient for complete resizing.

  10. jeepmor

    jeepmor Well-Known Member

    Agreed, however, sometimes you need camover to occur because of the press stretch BigJake mentions due to the high forces involved.

    Because of this issue, each time I setup my press (usually, sometimes I forget) I resize a few cases and then put chamber the empty case in the intended rifle to check for fit. I did this with my 300WSM cases and had to turn down my die another 1/4 to 1/2 turn before it chambered without a stiff bolt. Doing this resulted in that camover feel due to the stretching of the press itself.

    This would be particularly more noticeable in an aluminum versus cast iron press due to different tensile properties. But this also has to do with cross sectional area of the press, whether it's an O-press or C-press and so on. For the most part, O-presses and cast iron offer less deflection per unit force than aluminum presses. Without pulling out the old statics and strengths of material book, I can't comment more than that. Design features can make a huge difference in all these things. But long story short, the beefier the press, the better.

    Hope this helps,

  11. dmftoy1

    dmftoy1 Well-Known Member

    Man, I had to search like crazy to find out what you're referring to!!

    I took a look at the online dox for RCBS dies because I had never read that anywhere before. I finally found it in the instructions for the Cowboy Action dies at: http://www.rcbs.com/general/downloads.aspx#prod

    The text is below. My interpretation of their instructions is not to say that you can't cam over, BUT that you don't want to adjust the carbide sizing die down to touch the shellholder WHILE you are cam'd over as you would risk breaking the sizing ring later on when the press was at a higher point than it was during the cam over. (make sense?)

  12. Brillo

    Brillo Well-Known Member

    As a metallurgist perhaps I can shine some light on this. As long as I can remember RCBS has had the cam over warning on all their carbide dies. The reason is quite simple. The carbide material is quite a damage intolerant material. It’s very strong in uniform compressive situations, but will crack easily in bending or off axis loading situations which can happen in a loading press. Please realize that the force you can exert in the cam over position of the ram is tremendous – thousands of pounds per square inch. In deference to what one of the posters said above you don’t need to cam over to fully resize any cartridge, pistol or rifle. Now you still want to fully deploy the handle so it goes through the top dead center of its travel, so don’t be confused by this. If you adjust the sizing die (when properly tightened) so that it just touches the shell holder at maximum ram travel you will be fine. You can always feel the cam over in the handle if the dies touch, but if you are worried use a 0.001 inch feeler gage between the shell holder and the die. With the maximum deployment of the ram you should feel very slight resistance when pulling the feeler gage. You gain nothing by adjusting it further except unnecessary wear and tear on your press.
  13. uneasy_rider

    uneasy_rider Well-Known Member

    Brillo, I am not sure I am following. First, I am using steel dies, not carbide dies, and the instructions still say not to cam over.

    I screw the dies in until they touch the shellholder, then lower the ram, and screw in a quarter more turn.

    Will that allow cam over or not?

    If not, how do I set the die to get cam over?

    I have asked this a couple of times and no one can explain it to me in any way that makes sense. I need practical instructions on how to adjust the die.
  14. R.W.Dale

    R.W.Dale Well-Known Member

    Then you are indeed camming the press over against the die at the top of it's stroke
  15. Brillo

    Brillo Well-Known Member

    Cam over is not as much a problem with tool steel dies as they are a little tougher (not as brittle) than carbide dies, but you still do not need to cam over to fully resize a case. What RCBS means by cam over is that the dies come together and touch before the handle of the press has reached the end of its travel and “dead stops”. The cam over point is usually near the full deployment of the handle though. If the die is screwed too far down into the press and touches the shell holder too early in the stroke very high forces will be exerted between the die and the shell holder – forces much higher than necessary to fully resize a case. This condition is very easy to feel in the press handle as it is deployed towards its full stroke, dead stop position.

    When you set up your press put the handle at what would be the cam over position of the press (maximum upward travel of the ram) and screw the die down into the press so that it just touches the shell holder (with the lock nut tightened). This will allow you to pass the dead stop position of the press without the die and shell holder touching with appreciable force. That way you will be able to fully deploy the handle on each forming stroke of the press and rely on the dead stop of the handle to consistently form each case.
  16. rcmodel

    rcmodel Member in memoriam

    Cam-Over = All press frame flex, and linkage slop is forced out of the system when the linkage reaches full extension and cams over, or reaches center-line.

    To adjust a bottle-neck rifle sizing die properly: (Not Carbide pistol dies)
    1. Adjust the sizing die down tight against the shell holder.
    2. Then lower the ram and turn the die down another 1/4 to 1/2 turn. (depending on how much flex & linkage slop your press has in it.)

    You should be able to feel the ram "bump" the die tightly & "cam-over" at full press stroke without a case in the die.

    If you are not adjusting the sizing die this way, you are not setting the case shoulder back all the way.

    Smoke a sized case with a candle flame and try it in your rifle or case gage. You can then plainly see where the soot is rubbed off.

    You can then tell if it is due too the shoulder not being set back far enough.

  17. 30Cal

    30Cal Well-Known Member

    Are you using an RCBS shellholder with that die?

    I think it's time to pick up the phone and call RCBS. They'll be able to walk you through setting things up.
  18. snuffy

    snuffy Well-Known Member

    Cam over is not possible on some presses. Cam over is not DESIRABLE in some reloading circumstances. Setting ANY die/shell combo without a case gauge, is a lot like Russian roulette. You may need to have the shell holder and die tight together at the top of the ram stroke, BUT that might size the shell too much for some chambers, leading to head separations.

    As Brillo says, the stress on the press frame and linkage parts is tremendous IF set to cam over, if it's possible on your press. Most presses have need for lubrication at the linkage pivot points, the ram in it's bore, and other moving parts. Excess pressure from camming over squeezes the oil out of where it needs to be, allowing metal-to-metal contact. This WILL wear those pivot points out over time.

    If cam over is needed to allow full chambering of a shell, consider altering either the shell holder or die. Taking a few thousandths off the top of a shell holder will allow the brass to enter the die further. The same can be done to the bottom of the die, but once done there, it's rather permanent. Best way to do that is with a lathe. A file won't touch most dies or shell holders, and unless you're a skilled craftsman with a file, you're not going to be assured the die or shell holder remains square. Once altered a shell holder should be marked and remain with the sizer die. Using it for other dies will throw those settings off.

    EXACTLY! Tolerances in the press linkage, and stretch of the press frame will allow the shell holder to NOT contact the die due to the slack being taken up by pressure on/in the press. Set your sizing die up like the destructions say. Now lube a case and size it. Now take a strong light, shine it directly at the die/shell holder junction. I'll bet there's space between the shell holder and die. If not, then you're sizing as completely as possible with your set-up. If that's still not enough, then camming over will accomplish nothing,(other than wearing out your loader prematurely).
  19. USSR

    USSR Well-Known Member


    You're missing the point. The point is, not whether you have cam over or don't have cam over, the point is, are you moving your shoulder back too little or too much. Die manufacturers have no idea what make of shellholder you are using (and they DO vary in height), so they simply give you a rough estimate of how deep to screw your dies into the press (1/4 turn past contact with the shellholder, etc.). The truth is, unless you measure where the shoulder is with a tool such as the RCBS Precision Mic, or test fit in your chamber until the resized case "just" allows you to close your bolt in a boltgun, chances are, you have not setup your FL dies properly.

  20. BigJakeJ1s

    BigJakeJ1s Well-Known Member

    You NEVER need cam-over to accomplish correct sizing! Cam-over is simply a design/manufacturing feature built into some presses to account for tolerance stack up. The top of the ram stroke is the same whether the linkage takes you exactly to it, or past it (cam-over). No matter how much or how little stretch your press has, the ram will not travel past top of stroke, cam-over or not. More press stretch usually means you need to advance your die a little further past contact at top of stroke (adjusted with no load) than with a press with less stretch. As already mentioned, the amount of adjustment past contact also has to do with shell holder thickness. In order to know how much, you must measure or test your resized case in a gauge or the chamber in which it will be fired.


Share This Page