Run Out & O rings

[K22]

At the range today a fellow shooter was ravening about reducing run out by placing a rubber O ring under the locking nut of the expander ball assembly allowing it to "float" while full length resizing. He was using conventional RCBS dies which interested me since these are the same kind of dies that I use. This sounded logically and simple but I've learn that if it sounds to good to be true, well...

Have any of you tried this method and found it advantageous?

P.S. I remember reading an article by the highly respected German Salazar adovcating placing an O ring under the locking nut of the sizing die which is not the same as described above. I was reluctant to try this since I was concerned about obtaining consistent sizing with the die moving around and potentially becoming lose.

 

[BoydAllen]

There are bigger factors as far as concentricity with a one piece die. If you brush out necks, but leave some fouling, use a dry lube, such as Imperial, before applying lube to the outside of the case, and pull the expander through the necks....as slowly as you can manage. All of this after polishing the expander to a mirror finish. I always look at the die from the bottom and fiddle with the decapping stem until it looks to be well centered when the lock nut is tightened. By the time that the expander in in the neck, the case isn't touching the interior of the die.

 

[watercam]

I first heard of it from articles written by German Salazar. It does make nothing but sense as long as you index the dies to a specific 'crush' point with marks on dies and press that you can align. Being an old underwater guy I would add that a thin coating of silicone would help keep the O-rings from wearing and thus changing the relationship (distance) between the top of the ram and the die position.
Personally I seem to have been blessed with perfectly aligned ram face and die seating face - my run out with just about every die I use is just about 0.00 - 0.001". Can not explain it but my concentricity gauge is very happy!

 

[Zia Hunter]

I use o-rings on the decapping rods of my FL dies and in my case it has reduced runout. The lock ring should be just touching o-ring and not applying much pressure. Give it a try and see if it works for you. Based on my own personal experience, the single most contributing factor to runout when using FL dies is variations in neck wall thickness.

 

[necchi]

I've done it for years and it works great.

I de-cap with a Lee Universal de-capper, then size with the RCBS.

Another little tip if you do it like I do is to raise the inside neck button high in the die, it's not needed to be real low to de-cap as that's already done.

Guy's can beleive it or not but I consistantly get runnout of less than .0005-.001 with common RCBS dies useing this technique.

 

[spclark]

I've used o-rings under my die lock rings for years.

Took out the decapping pins too, along with the expanders.

I decap with a Wilson punch and base before wet-cleaning cases to keep grit out of my press rams.

Use expander mandrels too when needed, otherwise just bushings for sizing necks.

Starting with quality brass, runout averages 0.0" - 0.0015" on 75% of my cases firing after firing.

 

[1066]

I have been using the Lee locking rings on my Redding dies for several years.
The Lee rings already have the "O" ring in place and also it makes wince to screw a grub screw into the die body threads.

 

[CoverDog]

Below is the article by German Salazar

www.accurateshooter.com/technical-articles/reloading/o-rings-on-dies-may-reduce-run-out/

 

[mikecr]

I wouldn't put an o-ring under the die itself.
There is more to sizing than runout. We need the cases sized exactly the same.
Press flex, and springback of the brass, is enough to adjust for already without adding more variance.


Expansion by itself is another matter. This can be floated to self center without affecting sizing.
I hand decap, bushing size, mandrel die expand (it's floated).
http://www.neiljones.com/html/decapping_tool.html
http://www.sinclairintl.com/.aspx/pid=38807/Product/Sinclair-Generation-II-Expander-Dies

 

[BoydAllen]

Mikecr,

The die is restrained on the up stroke by its threads in the press, not the lock ring, that only serves to hold the dies rotational position relative to the press. Using and O ring under the lock ring, or a Lee lock ring allows the die and press threads to align true to each other. With a metal to metal fit between the lock ring, and the top of the press, the die can be locked down slightly cocked. I have a lot of experience doing it both ways. The only down side to the Lee lock rings is that it is easy to move the ring on the die when removing the die from the press. I have solved this by putting a split lock ring above the Lee, setting the die, and then snugging the split lock ring down onto the top of the Lee ring (shile being careful not to move it on the die) and then tightening the screw so that it is jammed into position against the Lee ring, and both rings on the die. I use this with an index mark for a starting point for fine adjustment of the die, and set up so that I have a little O ring compression (giving rotational position stability) at the highest point of adjustment that will be used (for new brass). Since brass hardens as it is repeatedly fired and sized the FL die must be reset as this happens to maintain the desired amount of shoulder bump. With the proper setup, the entire range adjustments can be done with one lock ring setting (with an O ring), without the Lee ring going metal to metal on the top of the press. Because I work with more than one set of brass, that have different amounts of work hardening, I reset my FL die for each lot, and at the beginning of each loading session, using my index mark as my starting point. It only takes a few tries on the first couple of cases to set the die, and by resetting it each time, I avoid accidentally using a hard brass setting on new brass, and having too much bump.

Obviously, to maintain consistency of work hardening, within any given set of brass, I fire and size in rotation, running through the cases to the end, and then starting over at the beginning.

I check my brass for consistency of bump and concentricity. Switching to the Lee lock ring has slightly improved the concentricity, and has not changed the consistency of the bump, so there is no disadvantage, and there is some advantage.

The other things that have given me straighter sized brass and straighter ammunition, are switching to a carbide neck bushing (more dimensionally correct) and switching arbor press seaters, to one that has a much closer fit on the case.

Because my loaded ammo had runout (on the bullet) that was less than .002 before I made these changes, the amount of improvement that could reasonably be expected was small. But each of the three things that I have described has made a contribution to improving the average concentricity of my loads.

 

[Immike]

I use Redding s- die. Take out the expander and only push in one direction. I dial the shell holder looking for imperfections and improvements. Then go thru a process of elimination till the crooked link is found. Then it's out!

 

[mikecr]

I'll look at it Boyd. When I can locate a dang indicator base around here, I'll check to see what die threading -preloaded only with an o-ring- allows for die movement under use.
I agree that the die needs to rest plumb to the ram/shellholder. But I'm predicting that preloading the threads to at least that applied with use, will reduce vertical die movement in the press.

 

[BoydAllen]

The whole purpose of the system is to size the case to the desired dimensions....so if the cases are good, we are good to go....and they are. My bump is consistent, and runout slightly better than a locked down die's. One thing that I have noticed is that having measuring tools can make us obsess on things that do not affect the outcome. Of course I have never fallen into that particular trap. One of the old timers in our sport once said that unless you can be sure that everything is perfect, that it is better to let it float than to lock it down. A locked die ring assumes that the bottom face of the ring is perpendicular to the axis of its threaded bore, that the top of the press is similarly perpendicular to the axis of its threads, that the threads are well centered over the ram, that the shell holder is concentric with the ram. IMO better a little float so that the die threads can at least center in, and have a chance to bear evenly on the press threads. My next little experiment, that I keep forgetting to pick up an O ring for, is to remove the spring clip that holds the shell holder in the ram, turn the rim of the shell holder that fits in the ram slot down a few thousandths, and fit an O ring to the external groove as a flexible retainer, that will require a little more work to change the holder, but not too much if the mod, improves results.

 

[Leaddog]

Previously had run out of .0005 (one half of one thousandth), now near zero using a #17 O ring between press and lock ring. I use Redding S type FL die and a Rockchucker press. The improvement is slight, but it is there.

 

[Chuckhunter]

I have a Co-Ax Press and it consistently produced straighter rounds than my single stage RCBS. After reading Germans article, I placed an O-Ring under the dies lock nut and also removed the spring clip that holds the shell holder and used an O-ring there also. Basically, I turned my threaded press into a Co-Ax and my single stage press now gives me ammo that is very straight and basically equals the Co-Ax. I'm not real scientific but I do know how to measure and my personal results indicate that Germans process works and I thank him for that.

 

[jo191145]

FWIW I removed the shellholder retaining clip years ago and replaced it with,,,err,,, nothing.
Takes a little getting used to but my ring finger was'nt doing anything else at the time.

 

[queen_stick]

FWIW I removed the shellholder retaining clip years ago and replaced it with,,,err,,, nothing.
Takes a little getting used to but my ring finger was'nt doing anything else at the time.

When I get home from work, I'm going to have to try that... never thought about it before. If I don't like it simply sitting there, I'll throw an O-ring on it.

while we're discussing it, I have a small single stage press from Smart Reloader.. the ram has a TON of play in it. I actually bought it for that reason, thinking that it might produce some straight ammo (it was cheap ). I haven't played with it yet to see if all that play is a good thing or bad thing. It seems like a light duty press, so I was thinking about using it for bullet seating and see what happens. One of these days I'll get it mounted and try it out.

 

[hogan]

Ain't the O-Ring supposed to be under the lock-ring, not the decapping stem locknut?

Don't want the decapping stem to float, not even if you have no size ball on the stem.


Ya wanna tighten your decap stem locknut once it is centered in a case's flash hole to center it.


Maybe you want to use a Universal decapping die and then size your brass after it's been deprimed?


Sizer ought to have the sizing ball on the upper end of the seating stem so that alignment is retained and
ball can be set to clear neck as deprime pin is clearing flash hole; or at least in aligment with it from insertion point.

Might be worth checking flatness of top of your press-to-die mount surface and the flatness of your depriming die lock-rings...

Also, talking bout Lock-Rings... The cross-thread fasteners like Forster uses and older RCBS die sets employed will not impart any cant of off-center effect to the die. I use Forster sliding die-chamber seaters. Would prefer the lock-ring from that die to be on my sizer than the seater. Getting the sized brass correct from step one is more important to me; but I use cross-fastening lock rings wherever I can...

 

[jo191145]

Ain't the O-Ring supposed to be under the lock-ring, not the decapping stem locknut?

Don't want the decapping stem to float, not even if you have no size ball on the stem.


Ya wanna tighten your decap stem locknut once it is centered in a case's flash hole to center it.


Maybe you want to use a Universal decapping die and then size your brass after it's been deprimed?






Sizer ought to have the sizing ball on the upper end of the seating stem so that alignment is retained and
ball can be set to clear neck as deprime pin is clearing flash hole; or at least in aligment with it from insertion point.

Might be worth checking flatness of top of your press-to-die mount surface and the flatness of your depriming die lock-rings...

Also, talking bout Lock-Rings... The cross-thread fasteners like Forster uses and older RCBS die sets employed will not impart any cant of off-center effect to the die. I use Forster sliding die-chamber seaters. Would prefer the lock-ring from that die to be on my sizer than the seater. Getting the sized brass correct from step one is more important to me; but I use cross-fastening lock rings wherever I can...

hogan

I heard years ago about the O-ring trick. At that time it was said to put an O-ring under the decapping stem lock nut if you use an expander.

The theory is the die sizing will give you the best possible run out scenario with ones particular set up. The expander thats allowed to minimally float will have a tendency to pull straight out even if theres "something" that wants to force it crooked. In other words it will have the freedom to follow the brass and not some defect in the stem/die configuration.
I have O-rings under all my standard dies decapping stems and never had a problem with depriming.

I realize theres a million or so arguements that could be made why this won't work. It works for me even though I have never checked any cartridge for concentricity in my life.
JMO but with a floating ball the lower the expander the better. Creates more float that way.

Your right, I found a rather large error in ram top to die stop face on my press. Filed the ram square with the die stop.
I can't imagine those two planes being different could help anything
Machinest types might have a better way but I felt good just doing that in Cro Magnon style.


Me personally, I would'nt want an O-ring under the die locknut but for all I know its beneficial.

 

[tensnxs]

I assume we're talking sizing dies on a thread down type press and this O-ring method isn't necessary on Forster's Co-Ax press?