Dwell Time When Sizing -- Any Actual Basis in Fact??

[ireload2]

The contrary positions to the .001 to .002 variations that are eliminated by adequate dwell time are:
1. You are claiming that slam bang operation of your reloading press will produce more consistent shoulder position than will slow deliberate operation of the press.

2. You are claiming that the meticulous maintenance of the shoulder position by FL sizing and by shoulder bumping produces worse accuracy than inconsistent technique when resizing your brass.

I think If you examine the contrary positions you will find they are very good arguments for carefully controlled press technique.

 

[BoydAllen]

Another variable in this is press linkage spring, which is why more consistent results are usually obtained if the shell holder makes contact with the die to the point of their being some resistance. Unfortunately this is not a method that can be employed in all cases, and the need to reset dies as cases harden makes custom fitting parts somewhat impractical. In effect the linkage of presses similar to the Rock Chucker operates as a very very stiff tension spring of limited travel that applies force to the case at the top of the stroke if the brass is resistant to sizing. This pressure continues to the point where the brass deforms enough to reduce it.

 

[Medic505]

I found a deal at an iron & metal salvage yard. The deal involved 30/06 cases

 

[riflewoman]

Another variable in this is press linkage spring, which is why more consistent results are usually obtained if the shell holder makes contact with the die to the point of their being some resistance. Unfortunately this is not a method that can be employed in all cases, and the need to reset dies as cases harden makes custom fitting parts somewhat impractical. In effect the linkage of presses similar to the Rock Chucker operates as a very very stiff tension spring of limited travel that applies force to the case at the top of the stroke if the brass is resistant to sizing. This pressure continues to the point where the brass deforms enough to reduce it.

A mechanical press applies a displacement not a force. The force comes from the resistance the brass exerts being reduced by the die. As some have said here in this thread, case lube, brass condition, grain size, brass thickness, etc, all play a part in this resistance. It should be noted that the Lee hand press is capable of FL sizing a 30-06 case so the forces created aren’t t that high. (I was told once by a tech at RCBS that resizing a case takes about 1200-1500 pounds but I have no data to confirm but it seems reasonable).

The upshot of this debate is there are too many variables to determine if dwelling is beneficial. But there’s no basis for it mechanically except for the deliberate action of the operating the press to the fullest stroke. Which is where some if not all of the variance lies.

 

[jimmymac]

As reloaders, we get in to habits that may or may not actually help. I fall on the dwell side of the equation. I also size, then give the case a little spin then size again. Once again, I do not know if this helps me. What I do know is that my brass sizes pretty consistently, the gun cycles smoothly and the targets tell me I'm not screwing up in my loading process, so I'll continue with my ritual. YMMV.

 

[Bart B.]

One can use a multiple compound leverage calculator...

https://en.wikipedia.org/wiki/Compound_lever

... to calculate force on case heads pushing fired ones into dies. Measure link lengths and angles precisely to get accurate results.

 

[BoydAllen]

I when the mechanical linkage of the press is stretched by the force applied by the operator and the stretching of the linkage stores some of that force, the press can continue to apply some force to the case even with the operator's hand in not on the handle. This is much easier to do when the linkage is made so that the ram is at its maximum height when the handle is in the full down position, stopped by the linkage. Essentially this is what makes dwell time have an effect.

 

[Howland]

If it takes several firings to expand the case shoulder all the way to the chamber shoulder, then controlling variability in setting the case shoulder controls case volume. The number of firings to get to end of case life is really a moot point for me. The higher the better but it's neither good nor bad, it's just a number.

You probably could never measure the effect on targets at 100 yards, but maybe at 300 yards, probably at 600, almost certainly at 1,000. The reloader controlling the process to +/-.001" is going to have an advantage vs. the reloader willing to accept +/-.003", especially given that the former is likely OCD enough to segregate brass by weight and eliminate the variable of brass thickness.

Perhaps someone with Quickload can calculate the difference in mean MV for the same load with case volume difference of .000168 cubic inches per .001" headspace variation (an extra 1.25g of water weight), then extrapolate that to difference in drop at 1,000 yards per thousanth. Yeah, I actually calculated that volume from the SAAMI specifications for .308 Winchester. That puts me squarely in the OCD group and, yeah I did just get 1,000 new IMI Match and weighed a representative sample and was disappointed to measure case weight variation of +/- 1.4%. I guess I'll be doing some sorting.

 

[fguffey]

I found a deal at an iron & metal salvage yard. The deal involved 30/06 cases

An arsenal issued a recall, the salvage company that purchased the brass was not given instructions, again, I thought the cases were magnificent cases. I do not believe the arsenal knew if the problem involved all cases but I do know many rounds of the stuff was shot as MATCHED ammo.

Like some members I am impressed with the speed the cases fly through those machines, I am more impressed with the annealing of the cases between the dies. And that is the reason the cases were being sold by the pound at the iron and metal salvage yard. Again, it was believe the arsenal decided it would be faster and cheaper to manufacture the cases if they eliminated one of the annealing process.

And one day I was at another iron and metal salvage yard in Yonkers, Yew York; they made me a deal I could not afford to pass up. They had 23,000 cases in buckets and barrels by the pound. All once fired.

F. Guffey

 

[fguffey]

It should be noted that the Lee hand press is capable of FL sizing a 30-06 case so the forces created aren’t t that high. (I was told once by a tech at RCBS that resizing a case takes about 1200-1500 pounds but I have no data to confirm but it seems reasonable).

All we need is a member with a strain gage, problem, reloaders deal in tension with no way to convert tension to pounds. I have tension gages, I should get my money back because all of my tension gages are calibrated in deflection and or pounds, I also have strain gages.

F. Guffey

 

[LHSmith]

F. Guffey[/QUOTE]

An arsenal issued a recall, the salvage company that purchased the brass was not given instructions, again, I thought the cases were magnificent cases. I do not believe the arsenal knew if the problem involved all cases but I do know many rounds of the stuff was shot as MATCHED ammo.

Like some members I am impressed with the speed the cases fly through those machines, I am more impressed with the annealing of the cases between the dies. And that is the reason the cases were being sold by the pound at the iron and metal salvage yard. Again, it was believe the arsenal decided it would be faster and cheaper to manufacture the cases if they eliminated one of the annealing process.

And one day I was at another iron and metal salvage yard in Yonkers, Yew York; they made me a deal I could not afford to pass up. They had 23,000 cases in buckets and barrels by the pound. All once fired.

F. Guffey

Did you get the junk brass from these guys?

 

[Bart B.]

No one calls using a rifle bolt to check the fit of brass measuring.

I think some do with a layer of tape on the case head.

Sort of, if not exact. It's part of the rubber ruler syndrome. Been done for decades.

 

[ireload2]

I am aware of that method but the tape is the measuring device. The bolt is still a non measuring part of the rifle.
The case is not usually a known dimension either.
I have a VZ24 with a long chamber. I do not have a 8X57 FIELD gauge so I used tape on my NO-GO gauge.

I think some do with a layer of tape on the case head.

Sort of, if not exact. It's part of the rubber ruler syndrome. Been done for decades.

 

[ireload2]

Not really.
The brass case is much more elastic than the linkage and is prone to yield. When the brass yields it creeps.
You can easily compute the area of the case walls and they are not much compared to the cross section of the press members under the same load.

I when the mechanical linkage of the press is stretched by the force applied by the operator and the stretching of the linkage stores some of that force, the press can continue to apply some force to the case even with the operator's hand in not on the handle. This is much easier to do when the linkage is made so that the ram is at its maximum height when the handle is in the full down position, stopped by the linkage. Essentially this is what makes dwell time have an effect.

 

[Bart B.]

I am aware of that method but the tape is the measuring device.

Few, if any, measure the tape thickness. A .006" spread across them is common. Rubber rulers are usually used.

 

[ireload2]

It is easy to measure the tape thickness. Fold the tape on itself so the adhesive sides stick to each other. Then measure the doubled tape thickness with a mike and divide by 2.
You can also use metal shims stuck together with grease.

Few, if any, measure the tape thickness. A .006" spread across them is common. Rubber rulers are usually used.

 

[Bart B.]

It is easy to measure the tape thickness.

I've done that for years. Tape companies oft times list tape thickness in their product data sheets.

How much does the adhesive compress by the measuring tool pressing on the tape? Bolt, too, for that matter.

 

[suasponte]

Maybe they want to learn about the 3 P's (process, perks and pitfalls) others experienced before establishing their own objectives, conditions and standards. They'll end up with better test methods producing reliable data.

My dad told me about the 7P's
P rior
P roper
P lanning
P revents
P iss
P oor
P erformance

 

[BoydAllen]

Not really.
The brass case is much more elastic than the linkage and is prone to yield. When the brass yields it creeps.
You can easily compute the area of the case walls and they are not much compared to the cross section of the press members under the same load.

If you limit the ram's travel by using say a Redding competition shell holder, shoulder bump becomes more uniform. If the linkage did not have some give, it would not matter. Call it what you will, one of the tested means for making bump more uniform is to physically limit the travel of the ram at the shell holder. If the linkage did not stretch, you would not be able to follow the manufacturers instructions(which, by the way are wrong, if you want any brass life) for setting up a FL die, because the press handle could not reach the end of its motion, so that the linkage reaches its maximum position based on a built in stop.

Another thing that illustrates this is the difference in the relation between the top of the shell holder and the bottom of the die that you can see when you set a die to just make contact with the shell holder with no case being sized and compare that to the gap that can appear at the top of the stroke when a case is being sized. Years ago, with a .220 Swift case and die, the gap went from nothing to .006". Most of us who have been paying attention have observed this. It is the reason that manufacturers have you adjust their dies past the point where they touch the shell holder. Of course if the rifle is not at absolute minimum headspace, the shoulder will be bumped back too far at that setting, but those instructions were written when brass was a lot cheaper.

 

[fguffey]

I've done that for years.

Not me: I have never found shims necessary, I have never found grinding the top of the shell holder necessary, I have never found grinding the bottom of the die necessary. The only thing necessary when grinding is to know how much to grind (for those that insist on grinding)

I have never found it necessary to purchase the go-gage, the no go-gage and field reject length gage. And then we have bumpers: If a bumper can bump? a shoulder back to get .002" clearance why cant he bump it back .005" or .008" or .010" etc?

And then there are short chambers, for me? Not a problem. I make gages for short and long chambers.

F. Guffey