Case Stretch after FL Resize

[Oso]

I was setting up to resize 223AI Brass (fully-formed and fired in my rifle) with a Redding 223AI Full Length Type S Bushing Die (.247 bushing) with Imperial Wax for lubrication. The FL Die is setup as per manufacturer's instructions and is making contact with the shellholder with medium cam-over pressure. While setting up the die, I was using a case micrometer to measure the shoulder bump. I was taking measurements from fire-formed cases, both before and after resizing, and it was showing a .001"-.002" growth at the datum line in the shoulder.

This turned into a science experiment - I set out 5 sets of 10 cases to run through several different shellholders (RCBS, Lee, Redding) with the plunger in the die and removed. The resulting measurements were fairly consistent with the stretch about the same for each shellholder. After removing the plunger (edit: expander button) from the die, the resized cases still showed case stretch at the shoulder.

I realize this is minor amounts of movement (0.001"-0.002"), but I am trying to bump the shoulder back that much, and not the other way around. Before I start flirting with some idea of shortening a shellholder, I sure would like to understand why the movement forward. What is causing the case stretch at the datum point in the shoulder? What am I missing???

 

[PopCharlie]

You're squeezing the brass like a tube of tooth paste. The brass has to go somewhere. I would screw the die down a little more. You will ultimately bump the shoulder back. You may need to trim the cases after sizing. Also, give each case a 5 count the top of the stroke. This tends to minimize spring back.

PopCharlie

 

[rwj]

Did you check if the sized cases (albeit longer) will fully go into battery? If yes, the cases likely have not yet have fully formed to the chamber which may require several firings. If they won’t go into battery, the offset from the die end face to the shoulder is longer than in the chamber. As the case is being radially sized, some of the material is moving forward towards the die shoulder. Correcting this will require material removal from either the die end face or shell holder.

 

[NorCalMikie]

And don't be trimming your brass till you know the "measured length" of YOUR chamber. Most reamers cut to about .020 "longer" than max trim length.

And if by chance you want to modify a shell holder, chuck it up in a drill press and run it down on an oiled sharpening stone. Measure first and grind as needed. It comes out looking like it came that way from the factory.

 

[D-4297]

Nobody has mentioned the good ole Fox in the chicken coop . Try removing the expander ball from the Die , and see what happens . Sounds like the expander ball may be "pulling" the shoulder back up as it's being extracted from the case . Some .223 cases tend to be very pliable and I learned this working on some "once fired" for a friend . Possibly running them through a small base Die first might aid insetting the base diameter , and moving the brass forward , before sizing them .

 

[wagonman]

my 260ai took 3 firings before they got snug, and then I bumped shoulder 1.5 thou. ackley cartridge's take a lot more blowing out to fully form to your chamber than standard.

 

[JMayo]

Cases can be pulled back up if not lubed well.
I had a bit of pull back today. When it's a strong pull back I run em up again not banging the shoulder.

 

[wagonman]

I was setting up to resize 223AI Brass (fully-formed and fired in my rifle) with a Redding 223AI Full Length Type S Bushing Die (.247 bushing) with Imperial Wax for lubrication. The FL Die is setup as per manufacturer's instructions and is making contact with the shellholder with medium cam-over pressure. While setting up the die, I was using a case micrometer to measure the shoulder bump. I was taking measurements from fire-formed cases, both before and after resizing, and it was showing a .001"-.002" growth at the datum line in the shoulder.

This turned into a science experiment - I set out 5 sets of 10 cases to run through several different shellholders (RCBS, Lee, Redding) with the plunger in the die and removed. The resulting measurements were fairly consistent with the stretch about the same for each shellholder. After removing the plunger from the die, the resized cases still showed case stretch at the shoulder.

I realize this is minor amounts of movement (0.001"-0.002"), but I am trying to bump the shoulder back that much, and not the other way around. Before I start flirting with some idea of shortening a shellholder, I sure would like to understand why the movement forward. What is causing the case stretch at the datum point in the shoulder? What am I missing???

embrace the idea of shortening your shell holder my ai redding die did what your experiencing grind the shellholder easy fix

 

[JFrank]

You're squeezing the brass like a tube of tooth paste. The brass has to go somewhere. I would screw the die down a little more. You will ultimately bump the shoulder back. You may need to trim the cases after sizing. Also, give each case a 5 count the top of the stroke. This tends to minimize spring back.

PopCharlie

They always seem to grow just before they bump...

 

[NorCalMikie]

And if you use "bushing bump dies", you don't end up pulling the necks on the up stroke.

 

[skeeljc]

An expander that is pulled back through the sized neck can distort the case (change the shoulder angle). Pushing an expander through a sized neck will have less effect on the case because the case is stronger in that direction.

 

[Bill Norris]

Removing that expander button normally does the trick for me.

 

[Oso]

Guys,

Thanks for all of the responses. During my testing I had removed the expander ball/button, which I mistakenly called the "plunger" and it still had case stretch. Also, I ran the test on cases that were 1x fired and 2x fired. Didn't see any real difference (everything stretched at the shoulder).

Tomorrow, I am back to the range to fire a few of the 2x cases for a 3rd round. At which point I feel very confident that they will be representative of this rifle's chamber (ignoring spring back). I then plan to modify one of the cases to use with the Sinclair chamber length gage to determine rifle's chamber length.

Based on tomorrow's 3x fired case lengths I will have solid idea of how much to remove/shorten the shellholder.

 

[Oso]

And if by chance you want to modify a shell holder, chuck it up in a drill press and run it down on an oiled sharpening stone. Measure first and grind as needed. It comes out looking like it came that way from the factory.

Thanks ... I hadn't even thought about using sharpening stone. This is way better idea to keep it flat then my plans to belt grind or diamond wheel.

 

[Oso]

Nobody has mentioned the good ole Fox in the chicken coop . Try removing the expander ball from the Die , and see what happens . Sounds like the expander ball may be "pulling" the shoulder back up as it's being extracted from the case . Some .223 cases tend to be very pliable and I learned this working on some "once fired" for a friend . Possibly running them through a small base Die first might aid insetting the base diameter , and moving the brass forward , before sizing them .

I just have clarified that I am using new LC brass and my rifle is bolt gun.

I have used small base dies for .223 Rem. to resize range brass that was fired through an AR15. I wasn't aware of a small base die for 223AI cases. How might this help my linear case stretch?

 

[fkimble@charter.net]

Seems to me a small base die would cause even more linear lengthening since it is reducing the diameter even more than a reg die.

Frank

 

[agr516]

When using a die that has an expander ball, using Hornady spray case lube can help a lot with that stretching. Just be sure to spray some into the necks of your cases from each side to help lube that expander ball when it pulls back through.

 

[RegionRat]

@Oso those results are typical. It is good to try and get a handle on the chamber size as you are doing. It does take a few cycles for the sake of getting an idea of the shoulder dimension.
I will add one caution to hold off removing material from the shell holder or die until after you finish stabilizing the measurement of the chamber’s requirements. Often you will find you don’t need as much bump, and that means a longer shell holder rather than a shorter one.
These shell holders are good to have for the example of where shoulder bump can be longer than a bottomed out die, while still allowing you to bottom the die. This minimizes the variation due to the stiffness of the press since the die can bottom on the shell holder and that is repeatable. BTW, even when you bottom the die, and have a matched set of brass, and use good lubrication, the shoulder dimension will still have some variation.

https://www.redding-reloading.com/online-catalog/35-competition-shellholder-sets

 

[Uncle Ed]

When you full length resize you are squeezing the case body diameter smaller causing the shoulder to move upward. Meaning it is possible to make the case headspace length longer than the chamber. It is the final part of the sizing ram movement that the shoulder is pushed back down.

With the Redding competition shell holders, you are told to start with the plus + 010 shell holder that pushes the case .010 "LESS" into the die than a standard shell holder. You then check to see if the case will chamber, if not you use the plus + .008 shell holder and push the case .002 more into the die. You keep working up with the plus + .006, +004, +002 until the case chambers without bolt closing resistance.

The bottom line, it is normal for the case shoulder to move upward, And it is up to you to set the die up to push/bump the shoulder back shorter than the shoulder of the chamber.

NOTE, in over 46 years of reloading I have only had to lap a shell holder once for a Czechoslovakian made Mauser .270 Win rifle with very tight headspace. Normally a sizing die will push the case shoulder back more than needed for your rifle.

 

[Coyotefurharvester]

Most important question, after sizing did the brass chamber(the way you want it to) ? If yes. Then the old spent primer trick, for determining space between case shoulder and chamber. If no, more sizing required, turn the die in 1/8. You will get there.