Case Growth/Shrink

[wkdickinson]

I bought 100 new Peterson SRP 243 "match quality" cases. When I got them I checked their length and while not as close to length as represented they were accepable. Now after 2 firing I decided to check the case length. They went from 2.038 to 2.045. I realize for 243, 2.045 is the max length. What I don't understand is why the big variation in length from the same rifle? Any thoughts?

 

[JohnKielly]

Likely the result of them expanding to fit your chamber.

 

[perazziguy]

No first hand experience with the 243 but my 22-250 cases grow. Depending on the load. On the lower end, not so much, up to true 22-250 velocity, trim required after every resize.
Jonathan Taylor

 

[wkdickinson]

My question really is about the lack of uniformity. If they grew or shrunk uniformly then I would have a better understanding of what's happening. I should have also said I am using a Redding Type-S FL Sizing die.

 

[Twicepop]

The case design of the .243 Winchester is the reason for the case growth. It has a goodly amount of body taper and a fairly shallow shoulder angle. Most cartridges designed up until the last 20-25 years share this common malady. Most every cartridge that can trace it's roots to a military cartridge have this problem also when pushed to their upper limits. When designed if they did understand that minimal taper and steep shoulder angles seem to be better for optimal accuracy, these were designed to be fired once and extract once with 100% reliability, reloading was not a concern. To stop the case growth, Ackley-ize the rifle, the almost non existent body taper and the 40 degree shoulder angle will stop case growth.

 

[Sniper338]

Your questions been answered!

 

[BoydAllen]

There are a couple of other factors involved. The amount that shoulders are bumped back when the cases are sized, and the amount of reduction in the body diameter of the fired case that the die produces. If one has a die that sizes the diameter(s) of the body minimally, and it is set to the minimum bump, there will be less case growth. Did you set the shoulders back after the first firing? Generally, that is not needed. I learned another lesson in this area from a .220 Swift. Shallower shoulder angles are more easily driven forward during firing. Keeping the bump to the absolute minimum gives the case less of a run at the chamber shoulder and minimizes the effect.

 

[Bc'z]

^^^^^what @BoydAllen said.
Another problem is tight dies.
Wilson just replaced a 06' die for me that was to tight dimensionally, forcing me to trim every firing, where my Redding type s didn't.
Same scenario with a 6x45 small base die by rcbs, agian Redding die fixed my issue.

 

[K22]

I'm not familiar with the "S" type dies but on standard full sizing dies if you are full sizing and don't make contact the shoulder of the case you can extrude the case and it will "grow" longer. So if you taking the measure after sizing this could be an issue.

Also, if you're taking the measurement before sizing and have not removed the spent primer you could be getting an erroneous measurement.

 

[Herzo]

You may have a headspace problem. I have 2 - 6mm Grendel AR's with which stretched cases are a problem as I was seeing head seperation. Checking new commercial ammo against the same cartridges fired from them showed the headspace to be on the high end. My solution was to purchase a set of 5 Redding shellholders from Bruno's Shooters supply. These will allow you to reduce the amount of shoulder setback by up to 0.010" in 0.002" increments. Just be careful to order the correct ones in that their numbers are all not the same as other manufacturers. Their .223 is a #10 whereas RCBS is #4.