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

[BoydAllen]

I just did a dwell test two nights ago between once fired and 5x fired lapua 260 brass. All annealed every firing. No dwell, slight dwell, and 2-3 second dwell all produced brass with the exact same measurements. Reason for doing the test was out of the same curiosity of the OP. Was kinda surprised with the results considering how often it is brought up. Test sample for once fired was 25 as well for the 5x fired. All brass was same lot.

I will continue to periodically measure to ensure the desired results, test be damned.

Of course, the annealing is the reason.

I have never annealed and would not be bothered for varmint work. I have always shot all the way through a batch of brass and then processed it, which has kept the number of firings and work hardening pretty consistent within batches. For target work I have almost entirely shot short range group and no one that I know of anneals for that use for reasons that are beyond the scope of this discussion. Of course it is common for long rang target shooting for obvious reasons.

I took the question to be whether dwell time has an effect and for regular, non annealed brass that has been used enough to be work hardened. It does.

One thing worth noting is that in order for the dwell time to have that effect your press linkage has to be such that the ram does not come back down any at the bottom of the handle's stroke, which a lot of fellows do not take the trouble to accurately determine. I suppose that you could do it on a press that did not have this feature but trying to stop the ram at the exact top of its travel would be way too much trouble for me. The softer the brass the less that this will be true.

I personally think that it is funny to be dependent on books for things that you can so easily test. It is like someone has no confidence in their own ability to observe. Certainly they are fine for discovering why something happens, but for simply determining if it happens I fail to see the need unless there is some sort of danger.

In conclusion I will say that I do not use dwell time to vary bump because it is an imprecise process, that depends on the work hardening of the individual case. I use one stroke for everything and try to rotate through batches to keep the work hardening as uniform as possible. Doing it this way has given satisfactory results for the applications that I have been involved with. If I start loading for a purpose where annealing will be advantageous, I will do it, but only if the results on targets tell me that it is the way to go.

Test everything and believe your targets.

 

[alinwa]

.........If there was any significance to the “dwell” theory, then the presses would have to run much slower.

"or they'd have to be set deep enough to compensate for bounce-back" (sorry, HADDA' say it LOL)


But ennyways, Thank You for this. For an informed viewpoint.

 

[ireload2]

As a doubting Thomas you would not believe anything we say either way.
If you do not have a highly accurate and consistent way to measure shoulder location there is no way for you to learn or be convinced or what the real facts are. The tool I use is a Stoney Point case gage now sold as the Hornady Lock and Load Case Gage. With my calipers it appears to repeat to .001".

It is easiest to understand this concept when forming cases. Some of these guys will have indeterminate or no results because they try to speak while only bumping shoulders of work hardened cases back about 1 or 2 thousandths. You also cannot just size 2 or 3 cases and get an accurate understanding either.

You also need to be honest with your own opinions and agenda. After working on process tooling, set up and development in manufacturing for more than 40 years I have seen many cases where personnel make a process fail because they don't like the process or that it was not their idea. That is just humans being contrary.

I first studied this phenomenon in detail nearly 20 years ago after getting the Stoney Point tool. I formed 100 new Hornady Frontier .303 Brit cases to 6.5X53R Dutch Mannlicher. My initial goal was 100% yield. With the cost of new brass so high and so limited in availability I had no interest in scrapping any or buying more.

I stripped the Mannlicher bolt to obtain the best feel of case fit.
I started developing the process using older cases that had been fired a variety of times. I initially tried to form the cases in one pass which resulted in accordioned shoulders except with a few FC cases.
The process that worked easily used 3 intermediate dies before the final sizing with a trim die. During process development I ruined about 15 old cases before I got all good ones. Then I switched to forming the new cases.
As I found the exact die setting on the trim die I checked the case shoulder position repeatedly as I snuck up on the exact feel I wanted in the rifle. Not every case reacted the same way to the final forming stroke. I has cases vary and because I measured each one immediately I began to notice variations in shoulder position corresponded to the force I had to apply to the press handle. All of the following affected the shoulder position:
1. More or less lube
2. Faster or slower sizing strokes
3. More dwell , less dwell or no dwell at the top of the stroke.
4. Multiple sizing strokes at the same setting vs one stroke. You might say more strokes vs fewer strokes.

I was working with new brass and you might assume that it was all the same.state of anneal. But you have to assume fired cases with different work hardening states will cause variations too.

When forming these cases a fast sizing stroke gave a longer case.
Too little lube gave a longer case. No dwell gave a longer case. One stroke gave a longer case than 2, 3 or 4 strokes. Beyond about 3 or 4 strokes the cases never got any shorter.

There is always the possibility of variation if your sizing technique dies not form the case shoulder to the fullest extent of your die setting. To consistently get the full sizing permitted by your die setting you need the following:
1. Uniform lube
2. Slow steady sizing strokes
3. About 3 to 4 seconds dwell at the top of each stroke. It really does take time for the brass to creep to its final position.
4. After the first stroke retract the case about 1/2" turn the case 120 degrees. Slowly size again with the dwell. Then retract and turn the case another 120 degrees. Then size again with dwell. Now check the case length from the head to the shoulder. It should be exactly the same as all other cases sized with the same technique.
If this seems like a lot of busy work you have to ask yourself if you want it fast or if you want it right. You do not get both at the same time if your calipers are honest.
It takes very little difference in technique to make the process vary by .002". Over the 100 formed cases mentioned I measured each one and checked the fit in the chamber 100% as each case was formed. When I got a case that was .001 to .002 longer it always corresponded to something that accidentally varied. Those longer cases were sized again until they matched the rest. As I learned what caused the longer cases I changed my technique and the variations went away.
I learned that lube, speed of the sizing strokes, multiple strokes and dwell time could all contribute to a much more exact and robust sizing process.

If you test enough cases you can reach your own conclusions.

 

[Murray Brook]

Riflewoman
With all due respect ammo companies deal only with new brass. The dwell time concept comes in to play with older brass. If I was always using new brass and only sizing once like the company then I could adjust my sizing die and not worry about dwell time. I would always get my .002-.003 bump. The problem starts after the cases have been fired a few times. In your experience is there a difference between the make-up of new brass vs old ones ? Does it's properties change with age or heat.

 

[alinwa]

As a doubting Thomas you would not believe anything we say either way.
If you do not have a highly accurate and consistent way to measure shoulder location there is no way for you to learn or be convinced or what the real facts are. The tool I use is a Stoney Point case gage now sold as the Hornady Lock and Load Case Gage. With my calipers it appears to repeat to .001".
.

IMO, there is a better way.

Simply size to a specific "feel" in your rifle. This is MUCH more accurate than measuring.

The technique is called "gauging."

 

[BoydAllen]

A lot of this depends on how the brass is built. For cases that have relatively thin shoulders it is less of a problem, but for some of the heavier built brass it can be a significant issue. A friend ran into this with cases with just a few firings on them, 7mmWSM and .338 Lapua. We could have simply increased the bump until the hardest loaded easily, but instead he bought a two torch rotary annealer that had an adjustable dwell time. With it we were able to keep enough hardness for hunting ammo fed from the magazine while softening shoulders enough that the total bump spread was .001. To keep that, annealing had to be done quite often. From that experience, I would say that for those cases there was excess variation in the factory annealing.

 

[ireload2]

No you are wrong which is typical for someone with an opinion that is not based on real experience.
Measurement to the nearest .0001" is far more accurate than your sense of touch. I do not have a means to measure with that accuracy but if I did I would sure use it.
Even so measurement to .001 is a real number that is quantifiable.
Measurement to touch does nit mean as much since touch from one person to the next is highly variable.
Like I said you can make it work or not depending on your personal agenda.

BTW gauging or gaging has different meanings. What do you call the use of a Hornady Lock and Load Case Gage? Gaging of course....

IMO, there is a better way.

Simply size to a specific "feel" in your rifle. This is MUCH more accurate than measuring.

The technique is called "gauging."

 

[LHSmith]

 

[6MMsteve]

where is Guffey he should have been all over this, maybe he be doing the Bump

 

[dgeesaman]

Us handloaders are an interesting lot.....for some reason snake oil seems to be an integral part of our repertoire.

I think the thing that comes up is coincidence versus causality.

Let’s say I’m working up a method or load and I note all of the things that went into creating it. How many of us simply recreate everything each time, rather than continue experimenting and removing things to eliminate the unnecessary elements. I suspect most of us go with the working method and don’t spend time or consumables trying to strip out the elements of it that don’t really contribute to the good result. If you ask what goes into that god result, you will have a lot of noise in there.

 

[Bob L.]

I was a structures design engineer for a major aerospace Company in the Seattle area for more years than I like. Does that count?

Counts for me, a structural engineer in commercial nuclear power for 35 years.

 

[Richard Coody]

whatever works for you.

to me inconsistent shoulder bumps are a sign of work hardened brass or something wrong in the sizing process. i anneal every firing for my precision rifles and have no problem having consistent .001 bumps.

 

[KMart]

You made me spill my coffee!

 

[ireload2]

Try watching the guys in a precision sheet metal shop bending 5052 H32 aluminum for a dozen years. It bends differently on the box flanges that run with the grain compared to the flanges bent across the grain. They also over bend the material to compensate for spring back.
When the work is critical they cut 10 or 12 extra blanks and test bend parts until the press is set just right. Then they bend all the parts from that sheet.
If they use another sheet they cut more blanks to test the setup. Then more parts are bent.

 

[nmkid]

I was a structures design engineer for a major aerospace Company in the Seattle area for more years than I like. Does that count?

But, have you ever stayed at a Holiday Inn Express??

 

[CharlieNC]

Funny @donovan we were just discussing this, and for the reason that it matters.

 

[riflewoman]

But, have you ever stayed at a Holiday Inn Express??

Matter of fact I have. The company was cheap when they sent me on travel.

 

[jds holler]

Thanks again for all input. Before I started this thread, I had just sized my batch of brass using a three second dwell at top-stroke. I don't have anymore fresh fired stuff to test with some of the methods mentioned.

Sorry, I don't have a comparator, and my primitive methodology will probably consist of gauging in my chamber for this batch that I'm loading right now. IF -- I don't notice any tight cases in this batch, I may take it as evidence that the dwell helped. I know this isn't really enough to be conclusive, and y'all can toast me for that if ya want.

Gotta go earn some more money right now to further my habit. Thanks. jd

 

[riflewoman]

where is Guffey he should have been all over this, maybe he be doing the Bump

He’s off somewhere doing the grind perhaps?

 

[ebb]

I think he has a sore back from taking his lathe with him where ever he goes.