Cam-Over: Don’t Do It. Just Don’t.

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This is a specially-adapted excerpt from the forthcoming book, “Top Grade Ammo,” by author Glen Zediker, owner of Zediker Publishing. Click here to order from Midsouth.

by Glen Zediker

My approach to some topics has changed over the years. It used to be that I would state my version of the truth, and explain its origin, and that meant also that anything not said didn’t matter, to me, or to the advice and instruction I was set out to deliver. Well. The internet.

camming linkage effect
Here’s camming linkage and its effect. On left is the maximum height attained by the ram; on right is the ram position at the full-limit stop on the press handle. It’s 0.020 inches on this press. As long as the shellholder is not being contacted, presses with this sort of linkage have a smooth feel to them and do a little more positive job of sizing. In effect, the case gets sized twice (the ram elevates again just as the press handle is lowered). Linkage, either way, has zero effect on setting up a die because you measure what you get anyhow, and adjust the die accordingly, after you see what it is that you got.

If you’ve kept up with the advice presented in this space on the better way to set up a case-sizing die, this next has already been dispelled, but judging from some of the emails I received asking questions, here’s a little more. I’ve fielded a few about “camming-over” a reloading press.

Some reloading presses, and RCBS comes first to mind, are designed with eccentric linkage. The concept involves circular motion and linear motion, meaning that when the ram traveling in a linear path reaches full extension, the linkage, which is traveling in a circular path, can move through the 0-degree mark and go to a negative degree. What that does is change the press ram position at the very top of its travel limit to a lower position. As the handle is drawn downward, the ram top reaches its maximum height and, at the last little bit, lowers. The amount varies in different designs. This action is an asset to attain flush-plus contact with the shellholder and the bottom of the sizing die, for them that wants it.

Now, any substantial press, whether it has eccentric linkage or not, can produce the effect of camming-over. A Forster Co-Ax, for good example, can just about crush a chrome bumper and doesn’t have eccentric linkage. To set up that press, any press, to cam-over, turn the sizing die downward beyond what provides full and flush contact with the shellholder when the ram is at its full height. Say, another 1/8 turn down.

Then, when the press handle is fully depressed, the additional pressure in the last bit of the handle stroke goes toward flexing the press. Simple as that, and that is what camming-over does: flex the press. That’s true whether it has eccentric linkage or not.

Don’t do it. Just don’t.

A press like this can be set up to “cam-over,” which is really just set up to flex. Any press with enough leverage can warp on itself. I’ve heard it said that the (excessive) lock down between press ram and shell holder “brings everything into perfect alignment…” No it doesn’t. Bud, if your press ain’t straight, bending it more won’t help. By the way, it’s one reason why cast iron is the traditional and proven material for presses: it has the characteristics that allow for flex without permanent change, even though it’s pretty rigid. It’s the parts that aren’t cast iron that bear the brunt of continual flexing. This is a Forster Co-Ax, a press design, favored by the author).

There’s no need to cam-over a press for a case-sizing operation. It stresses the machine and the tooling. Dies can get deformed and bent, carbide dies can break, and the press itself can suffer. I’ve known them to break. Some say that presses are designed to “take it,” but there’s an eventual penalty for repeatedly taking any machine to its limits. Ask any racer.

The main point is this: It’s not necessary. And it’s wrong. Going over the previous material on using a cartridge case headspace gage to determine sizing die positioning to get the correct amount of case shoulder setback, it’s clear that this sure should occur at a point shy of full contact of the die bottom and the shellholder surfaces. And, if it’s not enough, trying to push a case farther into the die by crushing the shellholder against the die isn’t going to do much. Folks. Done is done. The flexing might, maybe (maybe), increase setback 0.001.

If your sizing die doesn’t adequately set back a case shoulder, have a machinist remove metal from the die bottom. Best to use a surface grinder to avoid messing with the heat-treat on the die.

I’m rehashing a few things already covered because they’re germane to the whole camming tactic. Tooling manufacturers tend to suggest the “turn the die down to the shellholder, and then another xx-th turn…” to ensure that someone’s reloads are plenty short enough in headspace to fit any rifle made out there. As mentioned a few times back, I applied that tactic with a new Forster Full-Length .223 Rem. die (without adding any extra down-turns to cam-over the press) and that netted 0.008 additional case shoulder height reduction on a new, unfired commercial case. A foolish amount, in my belief. Since I then adjusted the die to provide 0.004 setback from fired, which was 0.002 taller than the new case read (on my headspace gage), it’s clear that this die is not touching the shellholder to produce well-beyond-safe shoulder reduction. One-eighth turn is about 0.009 inches.

Harrell Precision Sportsman press
If your press isn’t straight, get one of these, my day-in, day-out favorite of the “big” presses: a Harrell’s Precision Sportsman. Billet-made and precise, and very powerful. It doesn’t have eccentric linkage, just extreme strength and precision alignment. A press doesn’t have to weigh a ton to be strong, and it doesn’t have to be pressured to deliver dead-consistent sizing results.

To find out if you have a “cammer,” run the press ram fully up (press handle fully down) and thread a die in until it touches the shellholder. Try to move the handle back down. If it won’t budge, it’s got eccentric linkage. It won’t move because the ram is trying raise again. Back out the die until the handle moves and pulls the ram away. It’s at this point where “flush” contact with a die bottom will be.

Camming-over a press is a “feel-good” measure for some folks: there’s this satisfying “ka-thunk” at the bottoming limit of press handle stroke, and that lets a loader know that he or she gave it all they could get. It’s just going to be too much. The only time it’s not is for bullet swaging operations, but those aren’t on my list.

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25 thoughts on “Cam-Over: Don’t Do It. Just Don’t.”

  1. I shot some 280 Rem factory (Remington brand) loads in my Ruger M77. When I went to resize them, without camming over, they would not chamber in the rifle. I tried resizing them again, still to no avail. (Some Nosler brass that I hand loaded did not exhibit this same effect.) I pulled out the instructions for my RCBS dies and it said to set it up to cam over. I tried that and then the Remington brass from the factory loads would once again chamber. These Remington factory loads are the only thing I have ever had do this. I have not had this happen on my 280 hand loads. Any ideas why they would “need” the cam over, when nothing else seems to?

    1. After extensive testing and measuring of Federal Gold Metal Match ammo, and small base sized cases of as fired same FGMM, I have reached the conclusion that cases of factory supplied ammo are often sized smaller out of the box, than one can size a once fired, even using the SB dies.

      This explains the 280 report above. A tight chamber (one where the “go” gage just barely goes) will accept comm’l FGMM bottle neck cases out of the Federal Box new, but may not accept a case barely larger. Often times I cannot resize a typical bottle neck case (for instance .308) such that it is as small as the factory fresh case.

      It is obvious to me that comm’l mfg’rs want their ammo to fit all rifles, with nominal or tight case head space. Hence, their fresh case is smaller than you can make on your home press.

      ” Camming over” once fired cases, may help your reloads fit even the tight head spaced rifle chambers.

    2. I HAD SAME THING ON FRIENDS 280 W/150GR NOSLER PARTITIONS I RELOAD 4 HIM USING R-22 NO ISSUE AFTER THERE FIRED WITH MY LOADS I JUST THINK FACTORY LOADS IS TAD ON WARM SIDE REM BRASS IS ONE I BUY 4 MY DEER RIFLES NOT WIN BRASS THEY HOLD 1GR MORE BECAUSE THEY HOLD MORE POWDER BRASS IS THINNER AND THE WT OF BRASS IS TAD LESS ON SCALE DOWN FALL IN WIN BRASS BEING THIN AND LIGHTER THEY CRACK OR SPLIT IN SUCH SHORT TIME ONE TIP I CAN PUT OUT THERE MITE HELP U LOT IF U HEAT TREAT NECK ”’ANNEALED” HELPS ALOT IF THIS IS DONE EACH LOADING AND MUST BE DONE THE RIGHT WAY NOW SOME TURNS SHOULDER ORANGE WHEN ONLY THE NECK OF CASE NEEDS EVEN HEAT TIL U START SEEING ORANGE-ISH GLOW STOP THEN AIR COOL UR BRASS THEN SOME DOES WATER THING WITCH MAKES NO SENSE TIP OVER HOT BRASS IN COOL WATER I SET MY RCBS F/L DIE IN TIL IT TOUCHES THE SHELL PLATE I TURN IN JUST TIL I FEEL THAT BUMP AFFECT AND I NOTICE IF U USING LEE DIES U USE THERE #2 SHELL PLATE LIKE RCBS USE THERE #3 SHELL PLATE WITH UR 280 REM DIE ALSO IF UR STILL HAVING ISSUES BACK OFF UR POWDER CHARGE JUST TAD OR TRY ANOTHER TYPE SLOW BURNING POWDER MITE HAVE TO MUCH CHAMBER PRESSURE I USE REM BRASS FED 215M ALLIANT R-22 W/150GR N.P NO ISSUES RUN THEM OUT WIN70 BOLT 2680 FPS 15FT FROM CRONY ON A 40 DEGREE DAY

    3. A couple of things. First might be the base area needed the additional travel into the die, and, the die itself might be a little on the “long” side for headspace. At the most, at least according to my contacts at Forster, camming over might add a scant 0.001 to the sizing equation. I’m not certain, but since RCBS presses cam, their dies might be dimensioned around this.

      1. Thanks Glen. Your article has prompted me to try to figure this out. If I set the RCBS die to the spot where it is firmly engaging the shell holder, I get cases that are sticky (difficult to close the bolt) going into the chamber of the Ruger. This turned out to be true for both the Remingtons and the Noslers. ( I am not sure why the Noslers didn’t exhibit the problem the first time I tried it.) Knowing that the shell should have fit perfectly just after firing, I took one of each Nosler and Remington that were sticky and fire formed them using the Cream of Wheat method. As expected, they now fit just fine and chamber with the normal feel on the bolt. I have decided to replace the sizing die with one from Redding. I bought this RCBS set used, and possibly I got one that is either damaged or out of spec. I reload several other sizes as well as the 280 Rem, and no other die has exhibited this “problem”, and I use mostly RCBS dies. This was the first, and only, time I have tried the cam over thing.

        I am really enjoying your series!

    4. My 300wsm has the same problem, the shell will not chamber in the gun with out the cam over and the bolt will not close.

    5. Follow the directions. RCBS knows their designs better than anyone.

      As for the answer to your question; other than the possibility of you not actually going to just before the cam over point, I can’t really say.

    6. I wanted to feedback some results from shooting the 280 today. I shot 1/2 handloads of Nosler Brass, and 1/2 factory loads from Remington. Half of each I neck sized with a Redding Neck Size die, and the other half of each with a new Redding Full Size Resizing die. I wanted to eliminate the older RCBS dies that I purchased used on an auction site. No cam over was used with either die. All of the brass was then put through a Lee Quick Trim die. Every piece of brass fits the chamber perfectly with none of the earlier “sticking” issues I faced with the old RCBS die. I have concluded that the old die may have been damaged over time before I bought it, as it has always caused me the sticking issue with the Remington brass. I have several other RCBS dies that I bought both new and used and all work perfectly, so this in not trying to point fingers at RCBS.

      Interestingly, the Remington brass consistently required more trimming in both the neck sizing and the full length sizing, leading me to believe it starts out a bit longer from the factory than the recommended trim length. I appreciate everyones comments and ideas.

  2. I’m a reloader, but I have no idea what you’re talking about. Your discussion is just about incomprehensible. How about explaining what “camming over” is. Is it something that happens to the case? What does it look like?

  3. You need to explain this better. I cannot understand from what you have written what camming over is.

    1. A press with eccentric linkage, which means it’s engineered to lower the press ram height at the very bottom of the handle stroke, which meant that the ram attained a higher position prior to bottoming out the handle. So, if you thread a die in to touch the shellholder when the handle is fully down, then, in operation, the press ram will attempt to travel through the die bottom. Since that’s not possible, the press will flex. A press that doesn’t incorporate eccentric linkage can produce the same effect as a camming press by adjusting the sizing die to a position lower than “just touching” the shellholder. Either way, either design, we’re creating flex in the press from excessive ram/die contact. With eccentric linkage, the cam-over point is when the ram reaches its full extension and then lowers at the very end of the press handle stroke.

  4. For someone that claims to know so much about reloading, this article is surprisingly misinformed. Full length resizing is necessary for many rifles and is predicated on “camming over”.

    1. Not nearly. Setting a case shoulder back an entirely adequate amount for reuse is accomplished short of flexing the fool out of a reloading press. If it’s not, then there’s a problem with the die interior dimensions; any rifle that needs ammo THAT short isn’t likely capable of chambering factory ammo. Some of the chamber reamers used for “match” .308 rifles (military team specs) won’t allow the use of some commercial ammo because they are designed around Lake City M118 and M852, which is a little shorter than usual. That’s the point behind, for instance, the Forster “National Match” sizing die (it’s -0.003 in shoulder dimension). Most of the newer sizing dies I’ve had produce excessive shoulder setback, even on new commercial cases, if they’re threaded all the way down to the shellholder, let alone cammed upon. With the increase in semi-auto popularity, it seems that the sizing world is getting shorter…

  5. Great article! Love reading your material. Especially like your m14 stuff. So Forster does not recommend that you turn any further than flush? One other question slightly off topic. I have a Socom 16. some people recommend using a faster powder like IMR 3031 due to the shorter barrel. Is that necessary since they made the gas hole bigger? I’m thinking my trusty 4895 load should work just as good in the 16″ barrel as a 22″ barrel. Thanks in advance Glen!

    1. Honestly, I read die instructions but don’t follow them… Manufacturers err on the safe side and that’s understandable. They have zero control over what anyone does with their products. Again, that’s the whole point to understanding what we need to get from case sizing for OUR rifles, and why I’m pretty adamant about using gages to set it all up. Trust your numbers.

  6. I could never reason through the cam over directions that die manufacturers recommend so I often just set the die to “kiss” the shell holder (pistol and revolver). Seems to work fine for me unless I just want to bump the shoulder a couple thousanths which is most of the time on center fire rifle rounds. Thanks for a well reasoned article why cam over is unnecessary wear on equipment.

  7. Guess it depends on your setup. My Redding press cams over, but does not reverse direction of the ram at the end of the cycle. I use an RCBS gauge to measure headspacing of fired cases. I need the press to lightly cam-over in order to set the shoulder back between .0001 and .0002. If I remember, I screwed the dies approximately between 1/16 turn after bottoming out. I love my Redding press & dies. I do agree that excessive camming is unnecessary & can be harmful. As you mentioned, check cases with a gauge. If too much pressure if necessary to get the shoulder to set back slightly, then either have the shell holder precision ground down a couple of thousands, or purchase a shell holder that is custom made that is slightly shorter (Redding makes some).

  8. Glen:
    As usual your explanation is spot on!

    Thanks for your continued sharing of techniques that work.

  9. Mmmmmmm

    I load 6.5×55, 30-06 and .375H&H. RCBS press, all Lee dies.

    Every die set up is set to cam over, the camming action required very little so there is minimal stress on the components . The die kisses the ram and gently cams over. Unlike others I do not need hard cam over in order to get the case to chamber. The reason for using this setup is that you are guaranteed the same pressure on every stroke whereas when relying on the pressure applied by your arm this is variable.

    I have also found it impossible to apply the Lee crimp without some form of pressure control. Camming over does it perfectly. Relying on my arm pressure simply does not cut it, proved this time and time again.

    If the cam over is a thwack then I would agree as the pressures at this point are extreme. A gentle cam over has worked for me.

  10. I guess deleting my comment about manufacturers knowing what their equipment is meant to do proved me wrong.

    1. We don’t see where you had a comment deleted, Gary. Resubmit it. If you included a link, it may have been kicked out by the spam filter. This isn’t really a forum. Some links aren’t supported.

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