Press cam-over

[survivalshop]

  Here is an interesting read on Cam-over a reloading press over . Something I have done for a very long time , mostly because the Die instructions say to & it makes Case Head Spacing correct on my presses. I can see what he is talking about some presses that you have to watch out for the over cam'ing , but I never cam over all that much , I use very little & I've been using the same single stage press for almost forty years . 

 My Dillon 550B , I set up to just take the play out of the Tool Head , no cam over .

 

 

 

CAM-OVER: DON’T DO IT. JUST DON’T.

APRIL 14, 2016 MIDSOUTH SHOOTERS 2 COMMENTS

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.

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.

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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2 THOUGHTS ON “CAM-OVER: DON’T DO IT. JUST DON’T.”

1. Lyle Morton
   APRIL 15, 2016 AT 9:49 PM

   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?

   REPLY
   1. Glen Zediker
      APRIL 16, 2016 AT 7:30 PM

      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.

      REPLY