Forster Co Ax clone ?

[Unclenick]

HD,

Not only do the shell holders have the horizontal play, but another difference in that system is the shell rests on a platform that supports the rim all the way around with no gap as you have in a conventional shell holder. It may be a small factor, but it is better symmetry.

Earlier you said alignment was over-thought, but I'm going to suggest that proving something can't work by logic when experience shows it works anyway is also over-thinking. What is needed is, perhaps, a new analysis. It may be some other factor none of us have considered here. Or it may be that shell holder and the flat backing are the main trick.

That suggests another experiment. At some point, when they were on sale, I bought the Forster adapter for the Co-ax press that lets you use conventional shell holders with it. I had in mind to use it with the Redding Competition Shell holders, but that hasn't proved necessary, so I've never actually had occasion to try it out. But if I put it on the press and that deteriorates final round runout it would confirm the shell holder is the key difference. I'll have to think about that.

Another experiment that could be tried is taking a conventional press and swapping out shell holders. If you look at charts of shell holders from different makers, they don't use the same number systems and some brands will use the same number for two different cartridges that another maker has different numbers for. As a result, you can find shell holders for a cartridge that are looser in one brand than in another and that will provide some horizontal wiggle room. I have some Lyman and RCBS as well as Lee holders for the .473-0.010" head rimless cases ('06, 308, 45 Auto, etc.). Maybe one will be loose enough.

Well, now I've got more things to try than time. I'll bookmark this thread and come back to it when I have some results.

[hounddawg]

I use Redding fl dies for autoloaders and adjust the decapper when the case is in the die to ensure it is centered. It makes a big difference but still see some.003 and occasionally .004. Feel free to share techniques.

I found that if I decap before sizing and use no expander ball with a Redding S Bushing die I get less than .002, normally around .0005 - .0015. I did a test last year and compared that to using a Redding body die and a Lee collet neck sizing die and found almost no statistical difference

Just removing the expander ball and decaping rod rod and leaving the bushing adjustment backed off 1/16th of a turn to allow a little float in the bushing is my only "trick"

here is a 300 yd target from a match, my lack of wind and mirage skills killed the score on this one but 19 of the 20 rounds were a little over .4 MOA in vertical spread. The 20th shot at 11 o'clock in the ten ring would put it up to .6 MOA vertical

https://i.imgur.com/vA22xF9.jpg

The ammo did it's job, they guy behind the trigger was the weak link. Even if the group had been centered I would have still dropped 4 or 5 points so it's not great shooting at all but it does show what the ammo can do. You don't get vertical spreads of .5 MOA at 300 if your ammo has a lot of runout. The only real tests of what your ammo can do are conducted at the shootijng range. If you are getting small verticals then the ammo is working fine and no changes in equipment or load are necessary, those pesky horizontal spreads are the fault of the guy or gal pulling the trigger wind reading skills nine out of ten times. No amount of money spent on anything other than range practice change that

speaking of which it's time to pack up for a range session

[RC20]

edit - just watched a Forster video and I wasn't aware the Forster shellholders also have play in them. I thought the brass was held more rigid, I guess that gives them even more play so the die and the brass can align. They are nice machines and can see why people like them

Yipeee.

Sigh, no shooting unless I do it in the cold, range with the heat overhead is close till January.

[hounddawg]

RC you make me feel bad for thinking 55F and sunny is cold

Not only do the shell holders have the horizontal play, but another difference in that system is the shell rests on a platform that supports the rim all the way around with no gap as you have in a conventional shell holder. It may be a small factor, but it is better symmetry.

I am of the thought that the more play the better. The shell holder(jaws) job is to retract the case from the die when the ram( platform) lowers. Now I suppose when the shellholder or jaws allowed to retract the case if it tilts on the way out could tilt the case and possibly misalign the neck...odds are low but its something to think about. My thought is that the expander ball on the dies tend to tilt the case and that is why my runout is less when I remove the expander ball from the die

regardless I get great runout numbers the way I am doing things and while I wouldn't mind a new toy but I don't think a press is going to win out

[oley55]

edit note: comment deleted by myself

[hounddawg]

Oley 55, The die in a conventional press is locked, but the case floats for alignment. Put a case into the shellholder and wiggle it side to side, up and down and at an angle. That is your float. A good die in a name brand press should be within a couple of ten thousandths of center. You case has several thousandths play in all directions to allow itself to align to the die. If something stopped it from aligning you would ruin the case

[oley55]

edit note: deleted by myself

[hounddawg]

same way the case goes into the chamber, it is not perfectly aligned when you start closing that bolt but it aligns and enters the chamber because it is floating on the bolt head just like it is floating in the shell holder. It "chambers" in the die the same way it "chambers" itself in the rifle

@Uncle Nick, think you could maybe make a drawing showing how a case floats in a shellholder and aligns as it enters the die. A lot of people,such as my wife, can't visualize spatial relationships without a visual aid. You guys have no idea how many furniture mockups and scale models I have built over the years when buying or building new furniture and appliances over the years

Best way I can explain it is with the closing the bolt on case scenario. If you look at the bottom of your sizing dies they all have a radius chamfer to act as a 360 degree loading ramp. I can think of other examples such as pistons, hydraulic cylinders and rams etc. I used to work on this one high pressure pump. Only pumped a few cc's per minute but at 10K pounds output. Piston was solid alumina ceramic with no rings. The cylinder was a sleeve of silicon carbide. Replacing the piston was on the same principle, radius chamfer the cylinder and let the rod find its way into alignment

[Unclenick]

I'll have to think about how to present that. It needs to be exaggerated to be visible. The float is easy to show perpendicular to the case. But a case that starts into a die whose axis is imperfectly normal to the plane of the shell holder deck will be subject to asymmetrical stress and extra force leaning on one side of the rim during sizing. But in real situations that error is generally small. Most of the damage to coaxial alignment is, as you mentioned before, necks being pulled off-axis by a sizing die expander.

Someone had commented the ram in an old press of his had a lot of wiggle in its fit in the journal in the press frame, but that it seemed to work just fine. Extra float.

[reynolds357]

and on non co ax presses the case floats in a case holder and floats and aligns with the die....same thing accomplished. Nothing involving a floating object is precise. The precision lies in the dies. All the press does is just pushes them into and pulls them from the dies, as long as either the case aligns to the die or the die aligns to the case depending on which is floating then the two are pressed together then the mission is accomplished accomplished.

You take different presses and test the run out you get when seating, you will change your mind. I have 3 Rock Chuckers, a Lee classic and an Orange Crusher. Rock Chucker #2 gets all the bench rest seating. Crusher gets all the bench rest sizing.

[oley55]

edit note: deleted by myself

[hounddawg]

So back to my attempted point. If a brass case is held firmly in place (intentionally or accidentally jambed against the side of a shell plate with no wiggle room), and is then forced into a very solid and firmly held in place die, can you not see where the brass case would be reformed off axis?

of course it would, that is why the brass has freedom to move in the X,Y, and Z axis when it is in the shellholder which has been the point of every one of my posts. It ain't rocket surgery


Not trying to be insulting but I would think a airtraffic controller would just walk over to his press, place a piece of brass in the shellholder and wiggle it and immediately grasp the concept how the brass floats in the shellholder and aligns itself to the die as it enters it. If you can't see that then there is not much else I can do for you