A die float experiment

[BoydAllen]

Many years ago I did this experiment that was and I think still is unique. I came up with a way to give a die complete freedom to move in the threads of my Rock Chucker press, without being able to rotate. It is a simple setup that would be easy to replicate. The only part that required fabrication was a piece of steel that I found that was a couple on inches long and exactly the right size to fill up the slot in the top of the press that is designed to hold the primer feed tube assembly. I brazed a tightly radiused U shaped piece to one end that was slightly wider, between its "prongs" to accomododate the diameter of an extended set screw for a lock ring that was not of the split type, but rather the solid type that has a set screw that is at right angle to the axis of the die. I threaded this lock ring on the die so that it was several turns above the press with the die properly adjusted. In that position the long lock screw extended between the "tines" of my fabricated "fork" which was itself firmly clamped in the slot in the top of the press frame. With this setup I could test various FL dies by sizing cases first with the setup as described, and later with a conventional setup with a lock ring tightened against the top of the press. The results were not uniform. Some dies did better floating, while others sized straighter locked down. I will admit that this setup did not really allow much in the way of lateral shift. What it did do was to allow the die to shift around within the rather loose fit of dies within the presses threads. This would be an easy setup to duplicate. I think that a fork could be designed to be 3D printed. If it turns out that one of your dies does better with this sort of float than using this setup would be advantageous while also being inexpensive.

 

[three percent]

Ive wondered if lee breech lock presses would be better left floating the die rather than turned slightly more past the detent that snugs it tight?
Maybe not same thing your describing but would have to center up and hit threads same way

 

[BoydAllen]

Ive wondered if lee breech lock presses would be better left floating the die rather than turned slightly more past the detent that snugs it tight?
Maybe not same thing your describing but would have to center up and hit threads same way

If you want to see how loose my setup was, just screw a die into a Rock Chucker with the lock ring an eighth inch above the top of the press, grasp the top of the die and wiggle it around as far as it will go. The dies were pretty loose. In contrast, my Harrell's presses have a much closer fit to dies' threads.

 

[three percent]

I might try it both ways and see what happens.if I get any self centering improvement leaving it loose over locked down .
Good idea

 

[BoydAllen]

I might try it both ways and see what happens.if I get any self centering improvement leaving it loose over locked down .
Good idea

In my test some dies produced better results floating, while others did better locked down. If you do the test, pleas let us know of your results.

 

[Ray123]

I messed around with that idea, and it didn't seem to make much difference...nothing definitive. But maybe the Forester Co-Ax had the slight edge and it floats. I just test for runout if it's good it gets used. Also tried different seating inline micrometer Wilson and Forester micrometer were very close with the Forester Co-Ax press and Forester seating die.
There was an accuracy test with respect to bullet runout, In their test, it seem to make little difference on the 100 yd target on TIR all the way to .005" TIR with the .002" TIR the slight winner over the .0"- .001" in this test, with one rifle. But I just look at the runout ...if its good its loaded with that die press combo. Even a skim neck turned 50BMG can get nice runout figures with RCBS dies and RCBS press...I built a heavy duty fixture to check it.

 

[dcali]

If anyone has any interest in playing with this sort of thing, I'd be happy to design/print something to do the job.

 

[K22]

Using a conventional FL die, I experimented with German Salazar's No. 17 "O" ring under the lock ring to test, (1) the ability to make easy and quick sizing adjustments and to a lesser extent of interest, (2) to access improving run out.

In the first case, I could not obtain consistent and repeatable bumps. Perhaps due to the age of my press or my inability to align the die with "sharpie" memory marks method he used. I found that I obtained more consistent datum line measurements with my bump gauge with the die securely tightened on the press. Eventually, I evolved into using Skip Shims to make bump adjustments and this has worked extremely well for me.

On the run-out test, the results were inclusive. Perhaps the results were not reliable because I was using an old RCBS runout measuring device. But because of the undesirable results of the first case, this became a moot point since I was not going to use the "O" ring under the die.

For run out improvement, I experimented with placing the "O" ring under the expander assembly and raising the height of the expander button. Using the better Sinclair run out measuring device (on loan from a fellow shooter), I definitely saw a reduction in run out. However, this required a separate operation, depriming with a deprime die.

What surprised me was that the improved run out did not translate to improvement on target. Granted, I'm not in the ultra-precision game of benchrest or long-range shooting but I was still surprised. Consequently, I abandon the practice in favor of not having to add an additional reloading step (i.e., de-priming separately).

 

[BoydAllen]

Using a conventional FL die, I experimented with German Salazar's No. 17 "O" ring under the lock ring to test, (1) the ability to make easy and quick sizing adjustments and to a lesser extent of interest, (2) to access improving run out.

In the first case, I could not obtain consistent and repeatable bumps. Perhaps due to the age of my press or my inability to align the die with "sharpie" memory marks method he used. I found that I obtained more consistent datum line measurements with my bump gauge with the die securely tightened on the press. Eventually, I evolved into using Skip Shims to make bump adjustments and this has worked extremely well for me.

On the run-out test, the results were inclusive. Perhaps the results were not reliable because I was using an old RCBS runout measuring device. But because of the undesirable results of the first case, this became a moot point since I was not going to use the "O" ring under the die.

For run out improvement, I experimented with placing the "O" ring under the expander assembly and raising the height of the expander button. Using the better Sinclair run out measuring device (on loan from a fellow shooter), I definitely saw a reduction in run out. However, this required a separate operation, depriming with a deprime die.

What surprised me was that the improved run out did not translate to improvement on target. Granted, I'm not in the ultra-precision game of benchrest or long-range shooting but I was still surprised. Consequently, I abandon the practice in favor of not having to add an additional reloading step (i.e., de-priming separately).

forester decapping unit in rcbs die ?

I just installed a forester decapping unit in an rcbs die to try to reduce runout I believe that it is set up correct per forester instructions with the expander ball lower third lined up with the vent hole in the die , but I am still getting 4 to 5 thousandths of run out on most of the brass...

www.longrangehunting.com

 

[RegionRat]

Just going to point out a few things that I have encountered while helping to find sources of case runout for home reloaders, which is similar in many ways to production tooling.

The way tooling and dies are viewed in relation to each other when designing ammo production must include at least a 4 degree of freedom concept for the die and shell holder. There are two for translation or X-Y, and there are two tilt angles, Alpha-Beta.

First for background, each part of the system really has six degrees of freedom however since we don't care about the rotation along the die axis, or the shell holder, we can ignore 2 degrees for each and that leaves us looking at the main 4 which are the X-Y or position of the die, and the alpha-beta tilt angle rotations or how orthogonal the tilt of the centerline of the die is with respect to the ram axis. And...

Then, we consider if the shell holder surface of the die is tilted in systems that don't "cam over" since cam over tends to straighten the shell holder to the die axis in most press systems. That leaves the X-Y position of the shell holder with respect to the ram axis.

In all the discussion above, keep in mind that unless the shell holder is properly aligned to the ram, some distortion can be caused by the case bottoming out on the shell holder and being over constrained. If however the shell holder is properly positioned, the X-Y position of the shell holder no longer matters since the case will be translated on the clearance whin the die axis position.

In a normal situation, there is nothing stopping a case from translating or tilting in a shell holder. The shell holder alignment should always leave enough X-Y clearance for the case to float to the center of the die body.

Making sure the case can still float within the shell holder within the misalignment of the die is important.

The clearance of the case head to the shell holder is usually large enough that unless the press is a reject, the ram should place the shell holder within a reasonable target true position of the die threads.

That will leave us with the tilt of the shell holder with respect to the die body. Any tilt here distorts the case head to the axis, but the shell holder does not have any moment constraint on the case body when just pushing the case into the die. If the bottom of the die is pressed hard onto the shell holder, and they are cut straight, then at least the tooling doesn't contribute to the problem.

If we discover runout at the case head, it almost always traces to case wall thickness unless the shell holder tooling is way too tight or misaligned in X-Y.

Turning to the case forming and sources of runout in the plastic yield of the case near the neck, the wall thickness of the brass and inconsistent material properties are often the cause even when put into "perfect" dies.

So try not to drive yourself crazy with low quality brass which will "banana" no matter what you do.

I have also found that it is difficult to discuss runout no matter what, because it doesn't have standardized terminology. On an inspection print, we mark actual dimensions against the drawings, but in discussing it in the open folks may call things differently. It helps to be specific about case inspections and cartridge inspections.

Also, poor lubrication or running dry can cause enough shear friction to distort otherwise good brass, so again try not to run yourself in circles by not paying attention to your lubrication workmanship. The discussion above regarding pulling a ball expander through the neck, should always consider case wall thickness and lubrication to avoid going in circles.

Good discussion, carry on, as always....

YMMV

 

[BoydAllen]

IMO experiments dealing with variables that might affect case runout are extremely easy to do. All you have to do is size cases with and without the modification and see if there is a difference, and if there is, how much. Regarding the idea that shell holders have enough clearance to allow cases to align with dies, if the shell holder is off center on the ram that may not be the case. That is why several reliable sources have reported improvements from removing the usual shell holder spring clip in favor of an O ring. Test and believe your results.

 

[RegionRat]

Regarding the idea that shell holders have enough clearance to allow cases to align with dies, if the shell holder is off center on the ram that may not be the case.

I agree.
Sorry, I'm not a good writer, but was trying to point out that shell holder over constraint, or defect, is a very common cause for problems, so folks should also look down there, not just up at their dies.

 

[Gary in MD]

It’s been a while but I remember that there was an idea to help with the sloppy press threads and alignment of standard dies.
You needed to make a machined washer and take it and place on top of the shell holder as you raised up to the bottom of the die before you locked the die down. This would square the bottom of the die with the ram and shell holder. I’m probably not describing it very well and and it wasn’t floating the die but was supposed to help square thing up.
Gary

 

[Fairchaser]

I use a RCBS press with a hornady lock and load quick release rings that screw into the press and die allowing the die to be twisted into place with a 1/4 turn. The rings have an O ring that allows some play or slop which used to bother me until I figured it probably helped to self center itself. My runout is very good usually around .001-.002. Usually something with too much rigidity can induce problems. I agree with allowing some self centering to occur.

 

[Fuj]

If anyone has any interest in playing with this sort of thing, I'd be happy to design/print something to do the job.

Had an idea for the shell holder to be a type of ball swivel. It was
meant for something else but could be employed for maybe the
same principle.

 

[SeabeeKen]

I messed around with that idea, and it didn't seem to make much difference...nothing definitive. But maybe the Forester Co-Ax had the slight edge and it floats. I just test for runout if it's good it gets used. Also tried different seating inline micrometer Wilson and Forester micrometer were very close with the Forester Co-Ax press and Forester seating die.
There was an accuracy test with respect to bullet runout, In their test, it seem to make little difference on the 100 yd target on TIR all the way to .005" TIR with the .002" TIR the slight winner over the .0"- .001" in this test, with one rifle. But I just look at the runout ...if its good its loaded with that die press combo. Even a skim neck turned 50BMG can get nice runout figures with RCBS dies and RCBS press...I built a heavy duty fixture to check it.

I run a Forster and Redding BB2 side by side. Using the same dies, Ive seen no difference in dimensions or accuracy. Once in the die, the case was controlled by the die as long as it did not move than the play inside the shell holder.
@BoydAllen didnt you do a test comparing a loose ram and a tight press ram some yrs back? I recall someone doing it and the conclusion was that the loose ram was more accurate.

 

[dcali]

Had an idea for the shell holder to be a type of ball swivel. It was
meant for something else but could be employed for maybe the
same principle.

I've seen that done before - I can't recall where. It was an older press, and possibly modified? There was a ball in the base of the shell holder. In any case, I think the downside to this is that the ball doesn't allow for lateral movement. It would be better to put the ball under the shell holder, which is a good bit more complex.

 

[AlNyhus]

Excluding the die, the rest of the system has a very simple job to do. And that's to allow the case to self-center itself into the die.

Tight die threads, tight press threads, extremely close fitting rams, tight press linkage, tight shell holders, dies locked down to the top of the press...all these things (and more) get in the way of letting the die do the work.

Good shootin' -Al

 

[BoydAllen]

I run a Forster and Redding BB2 side by side. Using the same dies, Ive seen no difference in dimensions or accuracy. Once in the die, the case was controlled by the die as long as it did not move than the play inside the shell holder.
@BoydAllen didnt you do a test comparing a loose ram and a tight press ram some yrs back? I recall someone doing it and the conclusion was that the loose ram was more accurate.

No, I did not do that test, but I know of a very good shooter who intentionally took .006 off of his press rams to allow cases to center in dies. Although I have not seen any before and after runout figures, his shooting seems to suggest that it did not hurt anything.

 

[divingin]

Many years ago I did this experiment that was and I think still is unique. I came up with a way to give a die complete freedom to move in the threads of my Rock Chucker press, without being able to rotate.

How about putting a lock ring both on top and below the press head, set to be not-quite-tight? That assumes you have room to do so, of course.