Revolver case sizing depth ?

Status
Not open for further replies.
Been reloading for 28 years.......rifle and pistol......and I've always full length resized my handgun brass. I shoot tons of .38/.357 Magnum, 9mm, .45acp and .44 Magnum. All fully sized. I find no reason to partially resize the brass.

I've never seen instructions from RCBS that says; "the die should be adjusted to size only the portion of the cases that was expanded while being fired. Never try to sized the full length of the case as a small ring may appear, which is undesirable, and could weaken the case." Sorry, that's a bunch of baloney.

I just pulled up the instructions from the RCBS site ans this is what is says to do for carbide dies;

Sizing with carbide sizing dies
Screw the Sizer Die into the press until the die touches the top of the shell holder when the shell holder is brought up to the top of the press stroke. Tighten the large lock nut. DO NOT CAM OVER.
 
What's the purpose of 'cam over'? Once the die makes firm contact with the holder, any additional pressure is for naught as far as brass is concerned. Brass isn't moving any further into the die so all that additional pressure stresses the press/die. Sounds imprudent.
 
What's the purpose of 'cam over'? Once the die makes firm contact with the holder, any additional pressure is for naught as far as brass is concerned. Brass isn't moving any further into the die so all that additional pressure stresses the press/die. Sounds imprudent.
consistency is the reason, so the thicker brass gets sized the same as the thinner.

murf
 
45 long colt is the only handgun brass I partial size (3/4 of the length is sized). the 45 colt chamber is tapered quite a bit and if I fully size the case, the back end will rattle around in the cylinder. this only works in my gun since all chambers are different (some companies now actually cut straight chambers for this cartridge). case life is determined by the mouth, not the base.

luck,

murf
 
My old RCBS instructions that came with their carbide dies stated to screw the sizing die down till it just touched the shell holder and then to back it off the thickness of a matchbook cover so the die did not contact the shell holder when it bottomed out. This was to prevent the carbide ring from being cracked from pressure on the shell holder. It's what I have always done and it has worked well for me.
 
Been reloading for 28 years.......rifle and pistol......and I've always full length resized my handgun brass. I shoot tons of .38/.357 Magnum, 9mm, .45acp and .44 Magnum. All fully sized. I find no reason to partially resize the brass.

I've never seen instructions from RCBS that says; "the die should be adjusted to size only the portion of the cases that was expanded while being fired. Never try to sized the full length of the case as a small ring may appear, which is undesirable, and could weaken the case." Sorry, that's a bunch of baloney.

I just pulled up the instructions from the RCBS site ans this is what is says to do for carbide dies;

Sizing with carbide sizing dies
Screw the Sizer Die into the press until the die touches the top of the shell holder when the shell holder is brought up to the top of the press stroke. Tighten the large lock nut. DO NOT CAM OVER.
Been reloading for 28 years.......rifle and pistol......and I've always full length resized my handgun brass. I shoot tons of .38/.357 Magnum, 9mm, .45acp and .44 Magnum. All fully sized. I find no reason to partially resize the brass.

I've never seen instructions from RCBS that says; "the die should be adjusted to size only the portion of the cases that was expanded while being fired. Never try to sized the full length of the case as a small ring may appear, which is undesirable, and could weaken the case." Sorry, that's a bunch of baloney.

I just pulled up the instructions from the RCBS site ans this is what is says to do for carbide dies;

Sizing with carbide sizing dies
Screw the Sizer Die into the press until the die touches the top of the shell holder when the shell holder is brought up to the top of the press stroke. Tighten the large lock nut. DO NOT CAM OVER.
20191205_064943.jpg here's your baloney
 
More consistent than the die kissing the shellholder on every cycle?
the "cam over" applies to bottle neck rifle cartridges, not straight wall pistol cartridges or bottle neck pistol cartridges that headspace on the case mouth. it is very important to push the shoulder of the case back the same amount on every case as these cases headspace on that shoulder. different case wall thicknesses require different amounts of force to push the shoulder back, so the "cam over" requirement ensures the press ram travels the same distance every time.

if one adjusts the sizing die to just kiss the shell holder, the flex of the press body, when sizing a case, will cause the press ram to "come up short" and not touch the shell holder to the bottom of the die. setting the die to "cam over" assures that the shell holder touches the bottom of the die every time.

murf
 
What's the purpose of 'cam over'? Once the die makes firm contact with the holder, any additional pressure is for naught as far as brass is concerned. Brass isn't moving any further into the die so all that additional pressure stresses the press/die. Sounds imprudent.
" Cam over" is a fallacy that more consistent sizing is done when the case goes past top dead center and starts down again. Correctly adjusted dies with a solid stop are just as, or more consistent than running a case beyond top dead center. When "cam over" is used the die is adjusted to the point of sizing needed when the case goes as far as the press allows then starts down. Using dies adjusted for a solid stop, the die is adjusted so as to allow the case to enter so far and stop... (life long machinist/mechanic and 35 year reloading experience)
 
" Cam over" is a fallacy that more consistent sizing is done when the case goes past top dead center and starts down again. Correctly adjusted dies with a solid stop are just as, or more consistent than running a case beyond top dead center.

The rationale for "cam over" seems to be that if you have gone over-center, there can be no question that you got the die as far down as you have it set to go... whereas maybe stopping at what the user perceives to be the top might vary from case to case depending on the sizing resistance encountered.

I've never had a press that would cam over, so I just have to make sure I run it to the end of the stroke.
 
...if one adjusts the sizing die to just kiss the shell holder, the flex of the press body, when sizing a case, will cause the press ram to "come up short" and not touch the shell holder to the bottom of the die.
Gotchya. 'Coming up short' misses the kiss and 'press-body flex' sounds like an imperfect press for the specific job, OK for handgun ammo but precision rifle, no. Flex denotes variability. I get the gist but wouldn't load on such a press for rifle, bulk fodder excepted. I have a Redding T7 and haven't seen the need to cam over. Which common presses advise camming-over by their mnfr? Thanks murf.
 
Last edited:
A tiny bit of flex on sizing revolver cases is no big deal at all compared to the discussion of whether to size them all the way down or partially.
 
Gotchya. 'Coming up short' misses the kiss and 'press-body flex' sounds like an imperfect press for the specific job, OK for handgun ammo but precision rifle, no. Flex denotes variability. I get the gist but wouldn't load on such a press for rifle, bulk fodder excepted. I have a Redding T7 and haven't seen the need to cam over. Which common presses advise camming-over by their mnfr? Thanks murf.

I mean, if you were able to screw the die in and out, there's some play in the system.
 
'press-body flex' sounds like an imperfect press for the specific job, OK for handgun ammo but precision rifle, no. Flex denotes variability. I get the gist but wouldn't load on such a press for rifle, bulk fodder excepted.
I'd be interested in which reloading presses you believe not to have any flex

I have a Redding T7 and haven't seen the need to cam over.
Turret presses, by their design, have more flex than a single stage press...otherwise the turret wouldn't be able to rotate.

Redding minimizes the inherent flex in two ways
1. The rear support block that supports the turret after it is tilted back by the ram
2. The bushing which is machine matched to each turret to minimize flex while still allowing rotation...that is why it is important to keep bushings with their corresponding turrets

The following is a part of a missive from a Redding CS Tech...from 2016:

"A turret press has to have some clearance, otherwise the turret head
would not be able to rotate. There will be some deflection when
running a case into a die. With the T-7 the Turret Head will tip back
and make contact with the support block in the rear of the frame. At
this point the press is a rock solid as any single stage press. This
deflection has been accounted for in the engineering design of the
T-7 Press. The mounting surface of the turret and support block are
cut at different heights and each turret head has been matched to a
bushing that is .001" taller than the turret."
 
Last edited:
I mean, if you were able to screw the die in and out, there's some play in the system.
I don't have such a problem - zero play when the lock nut is snugged. If you have play after snugging the nut, something is amiss.
I'd be interested in which reloading presses you believe not to have any flex.
I don't know presses (no time or interest) like others around here so I'll defer to the experts. I'm not a br shooter but I see plenty of them use a Redding T-7, same as me. It's very adequate for my needs.

'Flex' is a nebulous term. Rhetorical: at what point does it become insignificant, fourth, fifth decimal place? That's for each of us to answer on our own terms.
 
I don't have such a problem - zero play when the lock nut is snugged. If you have play after snugging the nut, something is amiss.

I "don't have such a problem" either. I'm saying that there is necessarily going to be some small amount of give when the force gets high enough.
 
I'm saying that there is necessarily going to be some small amount of give when the force gets high enough.
I understand but we need to narrow 'small amount'. I doubt it's as much as a thou and I don't have an instrument to detect a ten thou or a hundred thou, but that's more mental gymnastics than significance to this shooter.
 
Agreed. As long as that tiny bit of give stays consistent, it doesn't matter at all.
 
I don't know presses (no time or interest) like others around here so I'll defer to the experts.
I'll give you a hint...they all flex

but that's more mental gymnastics than significance to this shooter.
Then why open the discussion of "flex" with statements like:'press-body flex' sounds like an imperfect press or Flex denotes variability. I get the gist but wouldn't load on such a press for rifle
 
Which common presses advise camming-over by their mnfr?
actually, some die manufacturers require "cam over". the requirement will be in the instructions included with the die set. I don't think press manufacturers have ever dealt with this issue.

luck,

murf
 
I mean, if you were able to screw the die in and out, there's some play in the system.
Yep, plus for any "machine" to operate there must be tolerances in the working parts, in this case there are several connections between the handle and the shell holder (aka linkage "slop"). Each connection will have some amount of tolerance and result in some movement between parts or else the parts would be "frozen", too tightly assembled and unable to move as designed. It may be in the thousandths of an inch, but it's still there...
 
Status
Not open for further replies.
Back
Top