.38 SuperComp Case Shrinkage

[Star4Ever]

Having just starting in the game with .38 SuperComp, and finding little if any real data on this caliber,

I decided to begin keeping stats and tracking a batch of cases to ascertain the case dynamics over their

useful life.

The cases are StarLine .38 SC. all from one large lot purchased recently. I have put 300 cases of the 1000

I have purchased into a firing pool. These cases will be reloaded as a unit and counts will be kept as to

number of times reloaded. Out of the 300 cases, 10 have been set aside as the virgin control group, not fired

and to be used as the basis of comparison.

After 3 loads and firings, here is a report on 10 random cases....

Starting with the new control group....

Overall case length for New Starline .38 SC:

Median = .8945" (the number closest to the middle of a set of numbers)

Mode = .894" (the number that most frequently occurs in a set of numbers)

Set Spread = .893 to .896

Now on to cases which have been loaded and fired 3 times:

Median = .887"

Mode = .887"

Set Spread = .883 to .889

Comparing the control group of unfired brass to the 3 times fired brass...

Average shrinkage per case = .0082"

Median shrinkage = .0075"

Modal shrinkage = .007

Worst case shrinkage = .013" Longest in control group to shortest after 3 firings

Best case shrinkage = .004" Shortest in control group to longest after 3 firings

So the numbers say there is some shrinkage going on after 3 firings.

The question is, will this continue at the same rate?

Tune back in after a few weeks and I will share findings...

[RH45]

I usually don't get enough of my sc brass back to actually keep track of, but, I inspect, and measure all my brass before reloading them, and when they shrink down to .88, I usually toss them.

[CocoBolo]

Interesting, I just shoot them till they split. I'll have to measure some. I do put them thru a CasePro before each loading, I'll measure some before and after the CasePro to see if they grow.

[Pat Miles]

What you are finding is actually compression. With the high velocities that the 38SC is shot at the base of the cartridge is pounded against the breach face during each firing and is compressed a bit. Full length resizing does not stretch the case as it does with rifle rounds. My last batch of SC had nine reloads on them before the primer pockets became loose enough to be replaced. Fortunately I get back almost 100% of my brass at local matches.

Pat

[latech15]

Are you measuring the fired cases after you have re-sized them or just after cleaning? It could be that your cases are bulging a bit (growing in Dia.) and shrinking in length and then once they are re-sized the length and dia. is restored. Are you using an undersized die for resizing?

I'm fairly new to reloading, but I have run probably 20-30k rounds. I have maybe 4000 pieces of sc brass and I haven't made it through the entire batch once. I just separate the ones that I have fired and mark the bucket that they are in as to how many times I have fired them.

[Star4Ever]

The measurements that I took were just after cleaning, not resizing. Interesting points made. I will resize a few to see if resizing extends the brass any. I suspect it will just a tad.

Thanks for the input.

[G-ManBart]

Cases will normally be a little shorter before you resize them. I've loaded some .38SC brass well over ten times, and they still worked fine. R,