So....cam over ?

[Webster]

So I've been using a lee challenge press for my entire 8-10yr lil reloading career. Well recently installed my late father in laws RCBS RCll press and started using it and I have to say is the first time I've really experienced this "Cam over" thing . I have it set for just a slight bit but honestly I love it and it really seems the ammo I've been making with it is much more consistent then with my lee. Shoulder bumps,ease of resizing,bullet seating ect all seem much more consistent, at least as good as my measurement skills will allow me to see lol ! Also I'm an over thinker and something about that lil cam over action just really really puts my mind at ease.

Anyhow I was curious what the pros thought when it cam to cam over on a press. Good bad ? Dose it help with consistency? I'm no f class or bench rest guy , just a dude who like trying to make decent ammo
Thanks !

Never understood cam over. Cam over is what the press linkage is doing, not how far the case is going into the die.

 

[BoydAllen]

Never understood cam over. Cam over is what the press linkage is doing, not how far the case is going into the die.

When you set up a FL or body die before you start sizing, if your headspace, die and shell holder combination is problematic, in that it is hard to get a proper bump, one that is actually needed, without which the case would be tight at the shoulder, here is a factor that can potentially solve your problem. I found it close to 40 years ago. The chamber was .220 Swift, the die a RCBS one piece FL die. When I set up the die touching the shell holder, and then looked at the setup with a case in place, with the ram at the top of the stroke, I saw a slim gap between the die and the shell holder. I grabbed my feeler gauge set and measured it at .006. I took this to be linkage stretch, on the Rock Chucker, and realized that I had an additional .006 to work with if I needed it. Beyond that I could go no farther, without modifying the die or the shell holder. Fortunately I did not have to. Sometime later I got the Stoney Point headspace gauge (now sold by Hornady), and discovered that I really didn't want the die that far into the press. The point is that for some situations where you have tolerance stack, you may in fact get a case farther into a die by adjusting past the point where the die touches the shell holder with no case in place. I hasten to add that I never set a die without careful measurement, and remind the rusty or novices that a full turn of a die lowers or raises it .071, so those that talk about going a quarter or half turn past are not IMO giving good advice for any kind of precison loading, with a FL or body die.

For a seating die, setting the press to toggle slightly can result in more uniform ogive to head measurements by putting a little stretch on the linkage so that the relation of the shell holder to the bottom of the die is more constant, instead of varying slightly with the seating force.

 

[Ccrider]

I have been using a Harrell’s combo doe more than anything else lately. I set my does up so that I get .0015 shoulder bump, cramming over at the end of the stroke a slight bit. If I have a case that is .002 after sizing, that is close enough and I see no difference on the target. If it is .001, I will spin the case and size again. I use to mark that case to see if it stays in the group. I have seen that it does not so I don’t worry about it now.

It is not hard to hold .0015 shoulder bump cammimg over. I have never tried with a solid contact on the shellholder. I use an arbor press to seat bullets for the most part. However, I have used the Harrell’s and a Lee die to seat bullets, both cammimg over. I had no problem holding .0005+\-seating depth with either.

 

[6MMsteve]

F Guffer would be all over this, don't stick your finger in the pourhole and never pick up a hot biscuit....cold chamber

 

[jimmymac]

How people get 100% dead nuts consistent shoulder bumps without shell holders making hard contact with the die, I will never understand. Or maybe they don’t. Or maybe they’re not measuring. Either way it’s absolutely astounding that this topic has not reached a consensus. I guess I don’t care what others are doing, but it still amazes me.

Full length sizing. The first step in reloading, ever since reloading was a thing, is up to interpretation.

I’m getting increasingly interested in these dies where a guy makes hard contact on the die and then adjusts the bump from the top. I think 419, maybe Cortina, maybe SAC, might be others. Game changer there

I'm shooting BR with dies that closely match my chamber. My die never contacts the the shell holder when sizing cases. I can hold my shoulder bump within half a thousandth. To me, that amount of deviation is white noise. All I'm trying to do is get the case to slip into the chamber without over sizing. I'm not splitting atoms.

 

[J.d. Popkes]

I'm shooting BR with dies that closely match my chamber. My die never contacts the the shell holder when sizing cases. I can hold my shoulder bump within half a thousandth. To me, that amount of deviation is white noise. All I'm trying to do is get the case to slip into the chamber without over sizing. I'm not splitting atoms.

Yeah that’s plenty good in my book. I just don’t have any luck unless I’m contacting. I messed with my Dillon awhile back, and found the same thing, huge variation unless I cam over and then I bump it 7 thou, which is not ok. I don’t know. I just know that I have my process figured out and don’t understand how else to do it.

 

[Steel Mover]

I cam over on only one forming step, on one case, then I change the die setting to a normal FL sizing for the one AR that uses that cat, which calls for a cam over in the initial forming process. Do not like to do a cam over, ever. Would rather run the die or the shell holder on my lathe to cut the few thousands space then set the bullet out.

 

[Old Navy]

Wouldn't you size too much if the sizer was screwed down to eliminate the gap or is this for seating only.

 

[RegionRat]

Yup, folks do need to pay attention to details like the concept of the modified shell holders or shims in these discussions.

Typical dies will bring the shoulder datum dimension below SAAMI specs if pressed down to flush with a common shell holder. While that suits some contexts, it isn’t what we are discussing or suggesting.

Sizing control means you still have to account for either modified shell holders or shims when discussing hard contact or cam over.

 

[Wolfdog91]

Starting to feel kinda stupid now honestly alot of this is going over my head for some reason. Not really white if I'm doing something special or what but all I know is I was able to get whatever should bumps i wanted at the time pretty easy even with cam over.
Just pushed my ram all the way up, screwed in my dit till it touched a shell holder then like a quarter (if that) of a turn plus.
Measure my shoulder size it. See how much it was pushed back. And then either screw in in a little.kore or less.
I mean maybe I'm not explaining cam over right ? Not the best at English sometimes I will admit. But yeah basically what I'm talking about is when my shell holder is touching my die it stops and if I add a little bit of force it's like it breaks over and goes to a little more and it locks I guess ... Idk I'm feeling kinda dumb trying to explain this could probably have one of y'all come and run my press hand once and know I'm describing something different or the same thing eveyones been talking about.
All I know my bumps have been way more consistent and my seating have been more consistent then with my little Lee press

 

[jds holler]

So, I just finished working up some loads for a friends 6 Remington, that he built in college. He'd never fired a round through it.

I had a couple of boxes of factory ammo for it, and acquired a pretty good quantity of used brass from a couple of you fine fellows here on the forum.

I was of course curious to see how much to size the cases to get started. I soon found that none of the used cases allowed anything even close to a fit in the chamber. I couldn't close the bolt on any of them, and some of them had been sized and deprimed by previous owner.

At least for this rifle, I had to set the sizer die jammed against the shell holder with definite "cam-over". After that everything was sweet, and the various brass all worked together to provide some very nice groups. I over looked the weight differences in them, (mostly +/- .003") and simply divided them into the two different brands. (win and rem)

Throughout the process of working with this gun, I just left the die to provide maximum sizing, and bolt lift remained easy, and this gun shot pretty durned good.

I've always assumed that the original instructions provided with a set of dies, providing contact with the shell holder is to provide SAAMI spec ammo, and I guess sometimes that's for the best. jd

 

[Kracken McGraw]

Starting to feel kinda stupid now honestly alot of this is going over my head for some reason. Not really white if I'm doing something special or what but all I know is I was able to get whatever should bumps i wanted at the time pretty easy even with cam over.
Just pushed my ram all the way up, screwed in my dit till it touched a shell holder then like a quarter (if that) of a turn plus.
Measure my shoulder size it. See how much it was pushed back. And then either screw in in a little.kore or less.
I mean maybe I'm not explaining cam over right ? Not the best at English sometimes I will admit. But yeah basically what I'm talking about is when my shell holder is touching my die it stops and if I add a little bit of force it's like it breaks over and goes to a little more and it locks I guess ... Idk I'm feeling kinda dumb trying to explain this could probably have one of y'all come and run my press hand once and know I'm describing something different or the same thing eveyones been talking about.
All I know my bumps have been way more consistent and my seating have been more consistent then with my little Lee press

Looks like you got it nailed to me. No use in trying to make it harder than it really is.

 

[Webster]

When you set up a FL or body die before you start sizing, if your headspace, die and shell holder combination is problematic, in that it is hard to get a proper bump, one that is actually needed, without which the case would be tight at the shoulder, here is a factor that can potentially solve your problem. I found it close to 40 years ago. The chamber was .220 Swift, the die a RCBS one piece FL die. When I set up the die touching the shell holder, and then looked at the setup with a case in place, with the ram at the top of the stroke, I saw a slim gap between the die and the shell holder. I grabbed my feeler gauge set and measured it at .006. I took this to be linkage stretch, on the Rock Chucker, and realized that I had an additional .006 to work with if I needed it. Beyond that I could go no farther, without modifying the die or the shell holder. Fortunately I did not have to. Sometime later I got the Stoney Point headspace gauge (now sold by Hornady), and discovered that I really didn't want the die that far into the press. The point is that for some situations where you have tolerance stack, you may in fact get a case farther into a die by adjusting past the point where the die touches the shell holder with no case in place. I hasten to add that I never set a die without careful measurement, and remind the rusty or novices that a full turn of a die lowers or raises it .071, so those that talk about going a quarter or half turn past are not IMO giving good advice for any kind of precison loading, with a FL or body die.

For a seating die, setting the press to toggle slightly can result in more uniform ogive to head measurements by putting a little stretch on the linkage so that the relation of the shell holder to the bottom of the die is more constant, instead of varying slightly with the seating force.

There are some things about presses and sizing that are subject to the stiffness of the press. They require a study and trade-off to see if cam-over or hard contact is the right way to go, or if you get away without it.

In the context of having a low stiffness press, and a high dispersion in the sizing force, you owe it to yourself to study the cam-over option. This option takes the press stiffness and size force dispersion out of the equation.

I don't think anyone has ever given the proper analysis of cam over. With the forces involved I don't see how you could bend or stretch a large piece of cast iron. I use very lttle force to size my cases. I pulled tensile specimens every day at a Reseach Center for 9 years. Some of the presses are said to have a rotory motion to the linkage. What Boyd said was interesting and I need to look for clearance as he did. Need to reread his post. My RCBS press has two large cast iron pieces that act as a positive stop for the linkage movement. Need to see if contact is made with the stop when I size.

My guess is that the ram comes up reaches a high point then the linkage comes over the top of the rotory cam like motion and then lowers a little. Isn't that the definition of cam over. Something like a car engine lifter riding up the cam lobe then lowering once it's over the top.

I need to try and exam the motion of my RCBS linkage and see if I can identify an over the top motion. Actually I don't worry about any of this I am happy with my ammo. I do feel a slight cam over when I size brass. Need to feel if the force on the handle increases or decreases during cam over. Without a die in my press it looks like the ram comes up and there is no unusual movement to the ram height at the end of travel. Any small downward motion on an up stroke would be had to see. Any force on the press lever should remove any clearance at pivot points.

 

[MagnumW]

STOP thinking about hard camover for sizing (shellholder truly firmly against die) unless you have modified shellholders or fancy $500 dies that adjust shoulder bump from the top .

You shove brass into the die until it meets a constant resistance (gap or light pressure between shellholder and die) or until it reaches a constant depth (hard camover between modified shellholder and die)
You decide which is the better constant to use - resistance or depth. If using hard camover without modifed shellholders you are most likely bumping shoulder excessively.

 

[BoydAllen]

I don't think anyone has ever given the proper analysis of cam over. With the forces involved I don't see how you could bend or stretch a large piece of cast iron. I use very lttle force to size my cases. I pulled tensile specimens every day at a Reseach Center for 9 years. Some of the presses are said to have a rotory motion to the linkage. What Boyd said was interesting and I need to look for clearance as he did. Need to reread his post. My RCBS press has two large cast iron pieces that act as a positive stop for the linkage movement. Need to see if contact is made with the stop when I size.

My guess is that the ram comes up reaches a high point then the linkage comes over the top of the rotory cam like motion and then lowers a little. Isn't that the definition of cam over. Something like a car engine lifter riding up the cam lobe then lowering once it's over the top.

I need to try and exam the motion of my RCBS linkage and see if I can identify an over the top motion. Actually I don't worry about any of this I am happy with my ammo. I do feel a slight cam over when I size brass. Need to feel if the force on the handle increases or decreases during cam over. Without a die in my press it looks like the ram comes up and there is no unusual movement to the ram height at the end of travel. Any small downward motion on an up stroke would be had to see. Any force on the press lever should remove any clearance at pivot points.

 

[RegionRat]

I don't think anyone has ever given the proper analysis of cam over. With the forces involved I don't see how you could bend or stretch a large piece of cast iron. I use very lttle force to size my cases. I pulled tensile specimens every day at a Reseach Center for 9 years. Some of the presses are said to have a rotory motion to the linkage. What Boyd said was interesting and I need to look for clearance as he did. Need to reread his post. My RCBS press has two large cast iron pieces that act as a positive stop for the linkage movement. Need to see if contact is made with the stop when I size.

My guess is that the ram comes up reaches a high point then the linkage comes over the top of the rotory cam like motion and then lowers a little. Isn't that the definition of cam over. Something like a car engine lifter riding up the cam lobe then lowering once it's over the top.

I need to try and exam the motion of my RCBS linkage and see if I can identify an over the top motion. Actually I don't worry about any of this I am happy with my ammo. I do feel a slight cam over when I size brass. Need to feel if the force on the handle increases or decreases during cam over. Without a die in my press it looks like the ram comes up and there is no unusual movement to the ram height at the end of travel. Any small downward motion on an up stroke would be had to see. Any force on the press lever should remove any clearance at pivot points.

If you think about your work in tensile testing, then you are familiar with how results can be skewed by trying to use the coarse position of the cross beam versus a properly placed extensometer.

All the contact points and lash in the cross beam position adds up to errors that are bypassed by measuring the deflection directly on the test sample.

So, if you picture the ram linkages, there are several simple pin joints with clearances, each one of them involved in the force path. The majority of the cam over stretch you feel comes from the slop being taken up and then the Hertzian Contact Stress/deflection of those joints.

As you pointed out, the sizing forces are often too low to account for bending or stretching the frame or linkages themselves, but the cam over deflections are mostly the result of the pins in their holes. The line contacts start to load up as the slop and tiny errors are taken up, and then the stiffness increases as the contact changes from points and lines into an area contact.

When you consider those stiffnesses and deflections in the linkages start up as the brass starts being worked in the die, and then continue if you cam over, it shouldn’t be difficult to imagine how cam over works in most presses.

The main concept is that when you account for dispersion in sizing forces, and that those forces and deflections may vary on the order of the desired shoulder bump, then cam over to a solid stack in hard contact takes the stiffness of the press out of the picture.

 

[Old Navy]

No cam over on my Rock chucker. It comes up to TDC and if the die is touching simply stretches all the slack out of the linkage. You can stick you head down under and watch the ram come all the way to the top. Forcing the handle down until it hits the stop does nothing except bend my linkage a little side ways. Yours might work different than mine?

 

[BoydAllen]

No cam over on my Rock chucker. It comes up to TDC and if the die is touching simply stretches all the slack out of the linkage. You can stick you head down under and watch the ram come all the way to the top. Forcing the handle down until it hits the stop does nothing except bend my linkage a little side ways. Yours might work different than mine?

From your post I get the idea that you actually do not push your press handle down until it hits the linkage stop. I think that that is not the way that the press was designed to be operated.

Reading a number of the posts in this thread I see something in common. Guys do not seem to understand that the instruction by the die maker to adjust the die an eighth to a quarter turn past the point where the die contacts the shell holder is essentially bad information, an oversimplification of the proper way to set a die for a specific rifle. Doing it that way pretty much guarantees that your ammo will fit in any standard chamber, but in that is not our goal for precision reloading. We are generally looking for a more precise approach. What really amazes me is that anyone would use a quarter turn past touch as a starting point for die adjustment. for a long time we have had excellent affordable tools with which to measure fired cases, so that we can set our dies so that the shoulders of our cases are not pushed back too far. The reason that we do not want to repeatedly push shoulders back too far is that doing that repeatedly will lead to case head separations, with the attendant sharp reduction of case life.

One thing that I often wonder is whether a reloader really understands how much farther into the press one turn of the die moves it. It is .071". What this means is that if you are trying to hit a precise adjustment, to say .001", moving the die that much feels like you may not have moved it at all. Generally speaking, here is the way that I tell shooters to adjust their FL or body dies.

Frist set your die about an eighth turn up from touch. From there you size and measure adjusting in tiny increments until you get the shoulder bump that you want. For once fired cases I suggest you duplicate the measurement of the fired case with your sized case and try it in the rifle. This is because it usually takes more than one firing for a case to get tight at the shoulder. There are some other little details worth discussing but I will leave them for answers to specific questions should anyone ask.

 

[Old Navy]

From your post I get the idea that you actually do not push your press handle down until it hits the linkage stop. I think that that is not the way that the press was designed to be operated.

Reading a number of the posts in this thread I see something in common. Guys do not seem to understand that the instruction by the die maker to adjust the die an eighth to a quarter turn past the point where the die contacts the shell holder is essentially bad information, an oversimplification of the proper way to set a die for a specific rifle. Doing it that way pretty much guarantees that your ammo will fit in any standard chamber, but in that is not our goal for precision reloading. We are generally looking for a more precise approach. What really amazes me is that anyone would use a quarter turn past touch as a starting point for die adjustment. for a long time we have had excellent affordable tools with which to measure fired cases, so that we can set our dies so that the shoulders of our cases are not pushed back too far. The reason that we do not want to repeatedly push shoulders back too far is that doing that repeatedly will lead to case head separations, with the attendant sharp reduction of case life.

One thing that I often wonder is whether a reloader really understands how much farther into the press one turn of the die moves it. It is .071". What this means is that if you are trying to hit a precise adjustment, to say .001", moving the die that much feels like you may not have moved it at all. Generally speaking, here is the way that I tell shooters to adjust their FL or body dies.

Frist set your die about an eighth turn up from touch. From there you size and measure adjusting in tiny increments until you get the shoulder bump that you want. For once fired cases I suggest you duplicate the measurement of the fired case with your sized case and try it in the rifle. This is because it usually takes more than one firing for a case to get tight at the shoulder. There are some other little details worth discussing but I will leave them for answers to specific questions should anyone ask.

I do hit the stop but gently. My press is probably 35 now and wants to twist a little to the right when it does. Maybe it is time to take it apart to see if I can tighten it up. Or is it time to upgrade?

 

[BoydAllen]

I do hit the stop but gently. My press is probably 35 now and wants to twist a little to the right when it does. Maybe it is time to take it apart to see if I can tighten it up. Or is it time to upgrade?

Got it. Thinking about it with my RCII I have always just stopped when I felt linkage stop contact. Doing that, I do not see a twist, and my sizing seems to be OK. Recently I bought a new RCBS press, the Rebel. The thought was to keep the one that seemed to be the best. I kept my old RC and returned the new one, for several issues that I won't go into here. One that I did not list when I returned it was that it acted like yours at the bottom of the stroke, doing a twist that my older press does not. Funny thing, the ram fit on the new press is slightly tighter, the reason that I think that it did it was that unlike the older press the stop surfaces were not machined. The were just as cast, with powder coating. Unlike the older press they did not make contact at the same time, which is what I believe caused the twist. I was disappointed with how this detail was handled on the new press. My advice to someone getting started would be to look for a clean, "low milage" RC II like mine.