Eric Cortina on setting the dies for shoulder bump

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PeteFox
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Eric Cortina on setting the dies for shoulder bump

#1 Postby PeteFox » Sat Sep 26, 2020 2:50 pm

I really like the way Eric goes about doing this.
No fancy clickable dies like the Whidden, just a straight forward method using stuff I‘ve already got.

https://youtu.be/htvk1UYOXm8

Pete

Gyro
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Re: Eric Cortina on setting the dies for shoulder bump

#2 Postby Gyro » Sat Sep 26, 2020 4:05 pm

Just another way to skin the same cat I thought Pete. Good in that he uses a few tricks that illustrate the fundamentals at work, which after all are everything.

I use the comp shellholder system which works well too, BUT ya gotta check the shellholders with a depth mike to make sure they are right ! Mine weren’t.

Annealing comes into this discussion too ( I think ) because even applying EC’s technique there will be some cases that don’t size like their mates ………. so maybe they are the ‘springy’ ones that need annealing ?

Perhaps the whole point of ALL this reloading metrology stuff is to properly understand wtf is actually going on and manage it ? Alas many don’t. And many won’t.

6.5x55ai
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Re: Eric Cortina on setting the dies for shoulder bump

#3 Postby 6.5x55ai » Sat Sep 26, 2020 4:41 pm

You can learn a lot from Eric. Like his vid this week where he loaded up a bunch of ammo, went to the range to test, and first shot was 250 fps over his normal velocity. Blew the arse out of the case. Massivly overloaded. End of range session.

Bigtravoz
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Re: Eric Cortina on setting the dies for shoulder bump

#4 Postby Bigtravoz » Sat Sep 26, 2020 8:05 pm

6.5x55ai wrote:You can learn a lot from Eric. Like his vid this week where he loaded up a bunch of ammo, went to the range to test, and first shot was 250 fps over his normal velocity. Blew the arse out of the case. Massivly overloaded. End of range session.


No couldn’t have happened! EC is the foremost expert on everything reloading, nobody has any idea compared to him! LMBFARO.

Redhawk
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Re: Eric Cortina on setting the dies for shoulder bump

#5 Postby Redhawk » Sat Sep 26, 2020 8:09 pm

Love the internet jockey comments:) Guess most with comments have the shooting results to support those egos:)

Good videos by Eric!

williada
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Re: Eric Cortina on setting the dies for shoulder bump

#6 Postby williada » Sat Sep 26, 2020 8:26 pm

Excellent choice Pete. Gyro you are right to mention annealing. The bump is important and the .002" covers variable expansion on the day. This highlights the fact brass is in a constant state of change and over time even if left alone it will harden. Its also important to sort brass by neck wall thickness too or turn it to constant dimension with a turning tool that is set and forgotten otherwise brass and pressures will be too variable. When brass is sized even from the same batch its chemical composition distribution in the brass may vary with a few cases after firing. You may find some have more springback even after annealing. You can mitigate this to some extent by leaving the brass in the die on the sizing stoke for a few seconds rather than rattling them through. Size, count to three then extract. Little things matter. There is the old saying about counting the pennies and the pounds will look after themselves.

pjifl
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Re: Eric Cortina on setting the dies for shoulder bump

#7 Postby pjifl » Sat Sep 26, 2020 9:10 pm

Most of these problems are bypassed by using a collet die. But maybe Eric does not want to know about that !

Peter Smith.

KHGS
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Re: Eric Cortina on setting the dies for shoulder bump

#8 Postby KHGS » Sat Sep 26, 2020 9:25 pm

pjifl wrote:Most of these problems are bypassed by using a collet die. But maybe Eric does not want to know about that !

Peter Smith.


Very good point Peter, I love collet dies. 40 degree shoulders tend to negate the need for regular shoulder bumping as well,
I love 40 degree shoulders too.
Keith H.

williada
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Re: Eric Cortina on setting the dies for shoulder bump

#9 Postby williada » Sat Sep 26, 2020 10:36 pm

I took the view fellas that Pete like a lot of guys wanted to know a straight forward method with the stuff they have already got. EC fulfills this approach well and is not pretentious or tongue -in-cheek in this posting. Nothing wrong with collet dies but there comes a time when shoulders and web have to be re-worked because of brass flow by full length sizing. On the down side when the necks thin with brass flow, collet dies can be found wanting. Alignment might be sound but pressure variables sneak in. The solution is to size the neck to the point a mandrel expands the neck to desired dimension. Both alignment and neck tension is then stabilised.

Gyro
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Re: Eric Cortina on setting the dies for shoulder bump

#10 Postby Gyro » Sun Sep 27, 2020 7:28 am

Pete, some personal rambling about our reloading techniques to get the gun to shoot : I for a time thought collet dies were the greatest and best way. Now those dies sit rusted in the back of the cupboard. And I heard guys were finish sizing the necks with a mandrel pushed through as the last step. I also made a few “reaming dies” and bought from Oz some Guhring reamers to be set up nicely guided in the die to cut out all traces of the dreaded doughnut. And I blueprinted all my dies so I knew they were straight. And I ran all tight neck chambers because I wanted to have perfectly prepared necks. They never were ! And for a few years I ran a special lube in the neck to prevent cold-welding between the bullet and neck wall so bullet release was consistent. Lots of time in the shed having fun. Then I went to a two day shoot and hadn’t done ANY of the above so just ran brand new brass and a hard jam and the gun shot incredibly well. That was three years ago and I only now think/hope I may have a gun that shoots as well. Quite frankly I suspect if ya have a gun that wants to shoot well it will likely tolerate any reasonable kind of reloading method.

Lots of fundamentals to attend to with the reloading Pete. Here’s one : be aware when trimming the brass OAL that ya not leaving a bunch of nasty jagged burrs on the case mouth, both inside and out. Some of these fancy cutter setups do a totally shite job of this ! DO NOT TRUST THEM. I’m building an inside-outside neck wall cutter now ( when I get time ! ) and the inside cutter head I bought is just crap and is never going to make a nice cut. After I have carefully stoned it hopefully it will be ok. Blah blah blah ……

Tim L
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Re: Eric Cortina on setting the dies for shoulder bump

#11 Postby Tim L » Mon Sep 28, 2020 10:03 am

williada wrote:The solution is to size the neck to the point a mandrel expands the neck to desired dimension. Both alignment and neck tension is then stabilised.

This is the bit I find flawed with bushing dies.
The process is totally reliant on the neck material to do what you want. ie compress evenly and subsequently expand evenly. I don't believe this is a reasonable expectation. It will "give" at the weakest point and compress/stretch at/from that point.
The lee collett die applies a force all round the neck. If there is a weak point it just moves first, once in position the die then moves the more resistant brass. ie the process is reliant on the tool, not the material. It may even correct those weak points by making brass flow radially around the neck (just a thought there, no evidence at all to support it)
The process is still reliant on the neck material for spring back but if all the brass is annealed this should be consistant regardless of weak spots.

Also, a personal, totally unproven theory, is that fl sizing is responsible for more brass flow than firing.
Firing applies an internal pressure, evenly, across the entire surface of the case. With no part of the brass free from this pressure, why would it flow? There is no unsupported point for it to flow to?

FL sizing, however, applies force at the base which is transfered to the bottom of the case wall first. As the case moves into the die that force moves up the die wall untill it reaches the shoulder. We then bump the shoulder. During all this the brass is having to move out of the way to allow the case to be forced into a hole too small for it. I would suggest it's exit point it the top of the case.

williada
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Re: Eric Cortina on setting the dies for shoulder bump

#12 Postby williada » Tue Sep 29, 2020 3:14 am

Never had a problem Tim. Yep, I anneal and together with a neck lubricated on the inside, use an aligned mandrel of correct size that matches my dies and custom chamber - its damn smooth, with controlled spring back. Yes, over working brass with dies that don't match the chamber will shorten case life. I design my chamber reamers to match my dies in FO. I don't send brass away to get the die to match the chamber as many do with custom dies. EC did a sound job on how to set up dies in the press which also promotes a proper working of the brass.

Other issues are created by neck reamers rather than by mandrels. I make my own. With reamers there is a tendency with the hand operated ones to leave marks and misalign the necks. More consistent results, at the future problem area of the junction of the neck and the shoulder can be obtained with an expanding mandrel right from the word go to align everything and give the correct clearance for the mandrel for neck turning operations for an appropriate and even wall thickness in the neck that balances gas seal and case spring back. Jim Boatright was a stickler on correct mandrel size in that operation. It takes about three firings to break in cases. New cases tend to shrink on the first firing particularly at the shoulder neck junction. A mandrel sorts that. I use a smaller diameter mandrel following neck turning and after case sizing is used to expand the neck to size, leaving that internal neck nice and smooth; and is critical in work hardening the case a tad after annealing to produce consistent neck tension and pressure. The slight working of the brass with mandrel in lubed necks also mitigates against donut formation which is a product of forward brass flow in subsequent firings. A collet die does not work harden the internal neck surface after annealing. This is where I think pressure variables sneak in with those dies. With everything there is a tradeoff with the variables. An Ackley improved case keeps the shoulder from stretching as far. Matching the spring back to the degree of shoulder bump required if any is less with Ackley cases.

Tim, you say, "Firing applies an internal pressure, evenly, across the entire surface of the case. With no part of the brass free from this pressure, why would it flow? There is no unsupported point for it to flow to?

Here's a couple of situations for you to consider Tim:

The greater the distance the shoulder is bumped back, the easier it is for the case to lie in the six o'clock position in the chamber. Most cases lie in the six o'clock position in the chamber and on ignition the case thrusts back onto the bolt face and the upper surface of the case expands before the lower surface because it has somewhere to go unsupported, then the brass stretches forward to engage the shoulder. In sloppy chambers this thins the upper wall and can lead to banana cases and bad run out or some degree of it. Then in subsequent firing the gas flow and turbulence in the case will vary. In the extreme, cases can be indexed. In match chambers this issue is small and indexing is not required but the issue exists. Ever wondered why new brass performs well compared to subsequent firings? In EC's video, you will notice how easily his bolt closes on the case. The case sits at six o'clock in that set up otherwise the bolt would not close. His tolerances are sound however and are a trade-off with other variables. He is getting consistent thrust on the bolt face.

If on the other hand, you like a jammed fit on the shoulder of the case, its not long before you do lug damage to the action camming the cases home. Lugs should be lubricated. One of the benefits of a jammed bullet, as opposed to a jammed case is that it centralizes everything because the case is relatively unsupported. In that scenario the brass flow is allowed to expand evenly contrary to your proposition. I always jam bullets on case break-in for that reason but also to create the correct spring back memory in the brass to facilitate an even wall thickness for less turbulence and alignment issues. I note Gyro's success with new cases which are probably .006" or thereabouts short of headspace would rest at 6 o'clock if he did not jam the bullet into the lands or close to them. New cases blow out and forward with the forward hot gas flow towards the muzzle. Hot gas softens the brass to allow it to flow more easily at the thinner neck wall in tapered cases. Ignition starts at the rear of the case with a greater volume of powder in a tapered case and gas flow moves forward from resistance to no resistance at the muzzle pushing the brass with it because the brass can't go back past the bolt face. Unburnt powder is doing the same thing. The case is also unsupported in the end of the chamber allowing the brass to flow more easily in the neck. Its not uncommon to see .020" or much more longitudinal case clearance in barrels. Some say there is a minimum of about .005". I go a tad more for safety when I trim. Problems arise here with carbon deposit if that clearance is reduced. Because brass does flow forward, case necks thin and donuts may form because brass is retarded at the shoulder. Collet dies are less functional for correct neck tension as the brass thins at the neck unless you can make an interchangeable mandrel or renew cases more often to match dimensions. If brass didn't flow forward I would never have to trim a case.

There is a final thing to consider with how the case sits in the chamber. EC uses .002", I go a little closer, but that depends on the brass composition. Some brass is harder than other brass. The point is that the brass will expand or contract with the heat of the day. I feel EC is accounting for that with a general figure. What varies is the tension on the barrel thread if the pressure on the case is inconsistent. This will interfere with harmonics and weak barrel joints, particularly with switch barrels.

Gyro
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Re: Eric Cortina on setting the dies for shoulder bump

#13 Postby Gyro » Tue Sep 29, 2020 5:28 am

Some more rambling : MANY cases come out of the box with doughnuts. They continue to form after firing for maybe 3 times then they go away. If ya do a super anal case neck reaming system ya get to notice this. Do donuts matter ? Not if your clearances and systems allow for them.

Brass does not allways thin out as it apparently moves forward. Sometimes it can thicken in the neck area and compromise clearances.

Ya run a hard jam on the 1st firing to avoid initiating case head seperation dynamics.

The amount of axial clearance that exists in the chamber between the case OAL and the 'front' of same chamber matters and needs to be understood and managed.

And collet dies are absolutely useless and no shooter ever using one wins hahah.

PeteFox
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Re: Eric Cortina on setting the dies for shoulder bump

#14 Postby PeteFox » Tue Sep 29, 2020 7:56 am

Wow, and I thought it was just a video about adjusting dies.
Pete

AlanF
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Re: Eric Cortina on setting the dies for shoulder bump

#15 Postby AlanF » Tue Sep 29, 2020 8:07 am

Gyro wrote:...The amount of axial clearance that exists in the chamber between the case OAL and the 'front' of same chamber matters and needs to be understood and managed...

And here's an inexpensive gadget that helps you do that :

https://www.sinclairintl.com/reloading-equipment/measuring-tools/case-gauges-headspace-tools/sinclair-chamber-length-gage-prod32925.aspx.


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