Cartridge shrink while drying in oven

Feb 6, 2013
319
71
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Copenhagen, Denmark
#1
After sizing and then wet-tumbling the cartridges I let them dry in the oven at 100°C / 212℉ for an hour. When I measure the cartridges afterwards they have shrunk from 50.95cm to 50.80cm (1.5mm) Testet with cartridges from the same batch. Cartridge that hadn't been dried in oven was 50.95cm and the ones who had been dried was 50.80

Is this normal?
 

pmclaine

Gunny Sergeant
Nov 6, 2011
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#2
Are they made of wool.

I think the physics would require brass to expand in heat (someone with brains will correct me on this).

Perhaps they do expand and they "spring back" more on cooling........

Im more familiar with the phenomenon of "shrinkage" in cold water but my experience has little to do with cartridges..
 

mijp5

Gunny Sergeant
May 7, 2009
4,804
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#3
After sizing and then wet-tumbling the cartridges I let them dry in the oven at 100°C / 212℉ for an hour. When I measure the cartridges afterwards they have shrunk from 50.95cm to 50.80cm (1.5mm) Testet with cartridges from the same batch. Cartridge that hadn't been dried in oven was 50.95cm and the ones who had been dried was 50.80

Is this normal?
move the decimal to the left
 
Likes: 1J04 and KZP

mijp5

Gunny Sergeant
May 7, 2009
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#5
Only thing I notice is that wet tumbling for over 2 hours, or even less time than that will often peen the mouths, and make the brass appear shorter, so pre and post tumble has the variance. But I am talking about a few thousandths. You are talking about 50 thousandths, which is insane. I would try setting the oven at 150 and checking
 
Likes: KZP
Jun 13, 2008
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#9
Are they made of wool.

I think the physics would require brass to expand in heat (someone with brains will correct me on this).

Perhaps they do expand and they "spring back" more on cooling........

Im more familiar with the phenomenon of "shrinkage" in cold water but my experience has little to do with cartridges..
hehehehe
 

pell1203

Full Member
Dec 27, 2007
1,025
154
63
Bellevue, WA
#10
After sizing and then wet-tumbling the cartridges I let them dry in the oven at 100°C / 212℉ for an hour. When I measure the cartridges afterwards they have shrunk from 50.95cm to 50.80cm (1.5mm) Testet with cartridges from the same batch. Cartridge that hadn't been dried in oven was 50.95cm and the ones who had been dried was 50.80

Is this normal?

:eek: Kristian, I've got to admit I got a few chuckles out of this too when I first read it, :) but we all have to start the learning process somewhere and asking questions is a good way to do it... so here is a straight answer with a few corrections along the way: :cool:

The case measurements provided are expressed in mm, NOT cm. Look closely at your calipers. If they are the digital kind, the button to toggle between Imperial and metric measurements is labeled "in/mm". With this in mind, the math below highlights the length differences you found.

50.95 mm - 50.80 mm = 0.15 mm size reduction = 0.0059 in. ( you can round up and just call this 0.006 in. )

That said, your shrinkage has nothing to do with the oven drying process and everything to do with peening the case mouths during the wet-tumbling process. Your tumbling media (assuming you are using steel pins) is effectively impacting or hammering your case mouths and slightly denting/deforming the mouths as suggested earlier by mijp5.

To completely convince yourself this is what's happening, run your experiment again. Size the cases as you did before, wet-tumble half the cases and simply rinse the remaining half to remove the sizing (no tumbling). Then, oven dry both batches at same time while still keeping the two lots separate from each other for later comparison. Once dry and cooled, measure cases from both lots.

You will find the cases run through the wet-tumbling process are shorter than the ones you simply rinsed. This should convince you that the oven drying had nothing to do with the observed shrinkage... or you can just take my word for it! ;) :)

(y)Two Thumbs Up! (y)
 

Spblademaker

Don’t tell my wife
Oct 24, 2017
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#11
If you’re worried about case shrinkage from drying them in the oven? Hell, dont ever take them swimming. quickly turns the 50 BMG into a 44 Mag.
 
Feb 6, 2013
319
71
28
38
Copenhagen, Denmark
#12
Yeah, it was a typo when i wrote cm instead of mm.

Anyway, I can see that no one has experienced the same. I agree that stuff would expand in heat, but the cases do shrink by approx. 0.15mm

It was the same batch and only half of the cases could fit in the oven, so I have half a batch that's 0.15mm smaller then the batch that never got heated. and no, I didn't swap the batch. The smalls ones are still on the oven plate and the large ones are still in a jar.