Understanding Press Cam Over...

[ArrowJ]

Sometimes die instructions will reference press cam over. I did a search and found what I expected...several "experts" that disagreed. Maybe we can muddy the waters more?

I am using a Redding Big Boss II which some guys said does cam over and some said does not. I used a Lee Classic cast in the past, and the same story. Also, some said it was a sign of a quality "modern" press, while others disregarded this claim.

Does cam over really effect how I set my dies, specifically my carbide dies?

[Bullwolf]

Sometimes die instructions will reference press cam over. I did a search and found what I expected...several "experts" that disagreed. Maybe we can muddy the waters more?

I am using a Redding Big Boss II which some guys said does cam over and some said does not. I used a Lee Classic cast in the past, and the same story. Also, some said it was a sign of a quality "modern" press, while others disregarded this claim.

Does cam over really effect how I set my dies, specifically my carbide dies?

While I don't use Redding a Big Boss II, I do have a couple presses that do cam over. It's pretty easy to see if your press does this or not.

Screw a sizing die down (don't use a carbide die for this) all the way until it touches the shell holder.

Can you move the ram still, or does it get stuck on the die from cam over?

If your press cams over, you will have interference between the shell holder the now flush sizing die, and will not be able to move the ram.

If it does not move, back the sizing die up a very small amount until you can move the ram again.

Cycle the ram again, watching closely between the shell holder and die for any cam over movement. If your press has any cam over, it's pretty easy to spot if looking closely this way. It's actually much easier to do this than it is to explain it.

The issue as I understand it with carbide dies is that the carbide resizing ring is brittle, and can shatter or break if pinched between the shell holder, and the die.

Also, the carbide ring in carbide die sets are typically only pressed in, or glued in. While you can potentially break the carbide ring... More often than not you will find that you simply loosened the carbide sizing ring, and it will fall out of the die.

I've had to re-install, or press back in in a carbide ring in a sizing die using heat/cold, and managed to keep the carbide ring back in place afterwards using Loc-tite.

I assume those are a few of the reasons why they say you should not bottom out a carbide die, when using a cam over press.

If there are other reasons that I am not aware of, someone else will likely mention them in this thread.

Cheers.




- Bullwolf

[claude]

FWIW I have zero experience with any Redding press, however every RCBS press I have ever used does have cam over, and no Lee press I have ever used has cam over.

The cam over is built into the linkage and the concept involves circular motion and linear motion, meaning when the ram which travels in a linear path reaches full extention, the linkage which is traveling in a circular path can move through the 0 degree mark and go to a negative degree. Another swirl of the mud, the linkage acts somewhat like a crankshaft on a car and allows the ram (piston rod) to break over top dead center (cam over) on RCBS presses, on Lee it does not.

[labradigger1]

For me, I prefer cam over for many functions including,
Bullet swaging, this allows me to to get exactly the same pressure on the squirt die and allows me to let go of the handle and let the pressure do the work. case sizing full length
Fwiw, my rcbs 2A is the press I use to cam over. I broke the Lyman tmag 2 the first time I tried to cam over.

[avogunner]

My press also "cam's over". It's my Pacific Mulit-C that is my first (and only) single stage press that I've used continuously for 35 years (since I started reloading in 1981). Honestly, until this thread, I just assumed all presses did that (well, really never thought about it) and you're supposed to adjust/set your dies when the ram at the top of the stroke. I did have the carbide sizer ring come out of a die once but it was a Dillon SDB sizer die and repaired it just like Bullwolf mentions but using a vice.

[Ole Joe Clarke]

I also have and use a Pacific Multi Power C, an "O" type press that I bought about 1975. It still works great, and I guess it cams over. Unless you swage, it's much ado about nothing.

Have a blessed day,

Leon

[ironhead7544]

At one time it was thought best to leave about a nickle sized gap between the shell holder and a carbide die.

[dudel]

At one time it was thought best to leave about a nickle sized gap between the shell holder and a carbide die.

My Hornady reloading manual said to run the ram to the top of travel, then seat the sizing/decapping die till it made contact with the shell holder.

The key part is running the ram to the top of travel, not necessarily till the handle hits the stop. On a cam over press, (using the crankcase example), the ram may be a bit below TDC when the handle it at the stop. If you set the die at that point, there will be more pressure on the die as the ram passes through cam over.

[ArrowJ]

So I called Redding. He said when using steel dies you touch the shell holder then lower the ram and screw the die in a little more, for carbide it is the opposite. Then he asked what cartridge and I told him 9mm at which point he confirmed what he said. This makes me wonder if it is different for different cartridges when the dies are steel. Either way, the procedure is as suggested above at least for the Redding Big Boss II.

[gwpercle]

My method of setting FL steel sizer , and this is for single stage "C" type press , Raise the ram, screw die down untill it touches shell holder , drop handle, lower ram and shell holder, screw die into press another 1/4 turn. If I can raise the ram fully , you will feel it "cam over " and come into firm solid contact with the die. If the ram will not cam over, back the die out until you feel it cam over and come in firm contact. It's something you have to play around with and you will get the feel for when it's right.
Without doing this you do not get total sizing effect.
With carbide dies the best you can do is to just touch the shell holder gently, if the carbide insert is pressed to hard it might crack...bad news there.
Steel dies are usually for bottle neck cartridges and carbide are for straight sided rounds. You can get steel dies for straight sided.
Gary

[dikman]

Interesting. I have two Lee Pro 1000's, both bought used, and the second one is obviously an older version - and it appears to have a "cam-over", as when the handle is down it has that slight extra movement that the other one doesn't. At least, I'm assuming that's what it is.

[DukeInFlorida]

OK, so here is the TRUTH on cam over, why, how, and when.........

1) Whether your press has cam over or not, DO NOT ATTEMPT to introduce cam over when dealing with CARBIDE dies. While carbide is very hard, and the smoothness of the carbide inserts allows you to skip the lubrication of the brass when dealing with pistol brass, the carbide insert is also very BRITTLE. If you try to over cam a carbide die, you risk breaking the carbide insert. Just don't even try to over cam any carbide dies. NOTE: Most pistol dies these days are carbide. Tighten the carbide pistol dies until they just LIGHTLY touch the shell holder. NEVER over cam those.

2) Rifle dies come primarily in steel dies (no carbide inserts). However, you CAN BUY carbide insert rifle dies. However, you should note three things:
A: Carbide rifle dies are made for the HIGH VOLUME commercial assemblers of ammo. The carbide provides them with extra long die life. Regular steel dies in a high volume operation would have to be replaced often.
B: Carbide rifle dies should NOT, just as is the case with carbide pistol dies never be subjected to an over cam situation. That will risk breaking the carbide insert.
C: Even if carbide rifle dies are used, the brass STILL NEEDS TO GET LUBRICATED prior to sizing. The carbide is there only to provide longer die life, there's still too much die to brass friction to get away without lubing the brass. Guaranteed stuck brass if you skip the lube. REPEAT: This is with regard to carbide rifle resizing dies.

3) Rifle STEEL DIES can, and should be over-cammed when your machine is able to do so! The steps for properly setting up your STEEL rifle dies is as follows:
A: Put the shell holder in the ram, and raise the ram to full or most upright position.
B: Do NOT yet put any brass in the shell holder, that comes AFTER "C"
C: Screw in the full length sizing die until it FIRMLY touches the top of the shell holder. Use a flashlight, and confirm that no light shines between the shell holder and the bottom of the die.
D: Lower the ram
E: Install a piece of LUBRICATED brass into the shell holder, and raise the ram to the top of it's stroke, and leave it there......
F: Use a flashlight again, and now check for light shining between the shell holder and the bottom of the die.

The light that you will see is because the press has loose tolerances between all the linkages. If you don't make an additional adjustment, you will not be bumping the shoulder back to it's SAAMI location. Remember, the shoulder does the job of sealing hot gases from blowing back into the chamber. The shoulder is a gas seal. So, another way to say this is that if you don't make an additional adjustment (lower) in the sizing die, the brass will NOT get properly full length sized. It's just that simple.

So:
G: Lower the ram with the brass still in it, and screw the die down a bit further. Continue adjusting until the bottom of the sizing dies completely touches the shell holder while full length sizing.

So, there are actually TWO ways to get there.

The better way is as I described it. Make adjustments until the spacing goes away while sizing.

The OTHER way to get there is to set the die so that it just touches the shell holder, NO BRASS IN PLACE, lower the ram, and just adjust the die so that it OVER CAMS a bit. That will achieve the same purpose.

If you don't properly adjust the steel rifle dies as described, you risk all sorts of situations:
1) Cartridges that won't chamber
2) Gases will blow by the improperly set shoulders, causing excessive blow back, reducing the life of the chamber
3) And, when gases blow back into the chamber, you also lose pressure that is supposed to be pushing the bullets down the barrel. Poor performance will result.
4) Eventual damage to the bolt, as the blow back can cause the brass to smash into the bolt face, creating excessive head space issues after a while.

I've been doing this stuff for almost 50 years now. And properly setting the die, per above has ALWAYS solved problems that students have called me about. I always show them the proper technique in my classes, and use the flashlight as PROOF of what's happening.

Try it, and see for yourself.

[ArrowJ]

Given all the problems caused by not setting it correctly for steel dies what prevents those problems from occurring when using a carbide insert die that cannot be adjusted down?

[M-Tecs]

I like presses that cam over. The advantage it that if your dies adjust properly with a cam over you can feel that everything is still in proper adjustment. Presses or dies that that don't allow cam over to solid contact work equally as well.

To properly set bottle neck cartridges that headspace on the shoulder for best accuracy and case life you should adjust the sizing die to give you .001" to .003" clearance on your chamber.

http://www.sinclairintl.com/.aspx/li...th-Sizing-Die-

The RCBS case mic is my preferred gauge http://www.sinclairintl.com/reloadin...prod33476.aspx

but the Hornady gauges work well also. http://www.hornady.com/store/Headspace-Gauge-Kits/

Over sizing leads to case separation or shortened brass life. http://www.larrywillis.com/case_head_separation.html

Some basics on headspace http://bulletin.accurateshooter.com/...ng-the-basics/

[DukeInFlorida]

Carbide dies are typically only available and used by hobbiest reloaders, and then ONLY for pistol and straightwalled rifle cartridges.

The issue of overcam for properly setting back shoulders deals with specifically the necked rifle cartridges. Use steel dies for those, and overcam, and you will never have a problem.

Now, the subject of true overcam comes up. TRUE, some reloading presses do not technically over cam, per se.

However, the steel dies can still be set such that the press will pinch the die tightly against the shell holder when the ram is in the full upright position. That will take all the stretch and play out of the press. Problem solved, even in those presses which do not, by design, over cam.

Given all the problems caused by not setting it correctly for steel dies what prevents those problems from occurring when using a carbide insert die that cannot be adjusted down?

[DukeInFlorida]

99.9% of the hobby reloaders are not needing those levels of precision, but do still need to properly bump the shoulder to SAAMI specs.

The long distance bench rest type reloaders take all sorts of additional factors into account when reloading. Shaving necks to assure controlled neck tension, etc... Those are all common techniques for bench rest shooters, but fall far outside the needs for regular reloading.

Over sizing brass always leads to lower brass life, but that's the nature of brass. If you have a bolt action rifle, I urge you to use a neck sizing only die, on brass already fired in that rifle, to extend brass life. But, for those of us who fire, say 308 Win brass in an M1A, or in an AR10, or those who reload 223 Rem brass for an AR15, we're stuck with full length sizing every time

I like presses that cam over. The advantage it that if your dies adjust properly with a cam over you can feel that everything is still in proper adjustment. Presses or dies that that don't allow cam over to solid contact work equally as well.

To properly set bottle neck cartridges that headspace on the shoulder for best accuracy and case life you should adjust the sizing die to give you .002" to .003" clearance on your chamber.

http://www.sinclairintl.com/.aspx/li...th-Sizing-Die-

The RCBS case mic is my preferred gauge http://www.sinclairintl.com/reloadin...prod33476.aspx

but the Hornady gauges work well also. http://www.hornady.com/store/Headspace-Gauge-Kits/

Over sizing leads to case separation or shortened brass life. http://www.larrywillis.com/case_head_separation.html

Some basics on headspace http://bulletin.accurateshooter.com/...ng-the-basics/

[M-Tecs]

But, for those of us who fire, say 308 Win brass in an M1A, or in an AR10, or those who reload 223 Rem brass for an AR15, we're stuck with full length sizing every time

Then learn how to adjust your dies for optimal headspace for that rifle to maximize brass life. If you want to maintain the cam over get the Redding competition shell holders. http://www.redding-reloading.com/ind...ellholder-sets

Good basics on proper die setup to maximize brass life here http://www.massreloading.com/bottlen..._resizing.html

One more option for measuring shoulder proper setback http://www.larrywillis.com/

more options http://bulletin.accurateshooter.com/tag/shoulder-bump/

[country gent]

The other benifit of over cam not mentioned here is it helps to take the play out of the mechanisim of the press. All mechanical things need some clearences to function smoothly and easily. some clearance is also needed to account for slight miss alighnments and crud during use. A press that cams over goes to top of stroke and as the linkage moves past top dead center drops back down slightly. This helps to maintain a consistant top dead center hieght of the ram. As links pins and parts wear in this over stroke will slowly increase.

[DukeInFlorida]

Yes, it was mentioned. The play in the press ***IS*** the reason why you need to overcam necked rifle brass with steel full length reloading dies.

Please re-read my lengthy explanation:
http://castboolits.gunloads.com/show...=1#post3565688

[dverna]

Then learn how to adjust your dies for optimal headspace for that rifle to maximize brass life. If you want to maintain the cam over get the Redding competition shell holders. http://www.redding-reloading.com/ind...ellholder-sets

Good basics on proper die setup to maximize brass life here http://www.massreloading.com/bottlen..._resizing.html

One more option for measuring shoulder proper setback http://www.larrywillis.com/

more options http://bulletin.accurateshooter.com/tag/shoulder-bump/

An excellent post sir!!
Thanks
Don Verna