7.65x17 Case capacity


#1

Hello guys!

My question is exactly as the topic’s title, what is the case capacity of 7.65x17 mmSR Browning (.32 ACP)? I tried calculating (rough method) myself as follows: half the bullet diameter squared * pi * case length. Converting it to cubic centimeters, I got 0.8566 cm3 (13.22 gr).

Also, I’ve done it secondly by subtracting 0.3 mm from 17.3 (case length), this being the length from base of the cartridge to the beginning of the case. I got then 0.8417 cm3 (13 gr).

I even tried applying the volume formula of the truncated cone using some values from CIP and SAAMI. I got 0.91 cm3 (14.04 gr). Strange as my values tend to raise compared to the ones contained on this page which are halved - https://www.thehighroad.org/index.php?threads/why-is-it-so-hard-to-find-a-list-of-case-capacities-online.582478/.

So, where am I wrong and what’s the exact value? Would you find them in the CIP or SAAMI data sheets? (I have not…)
And I also ask you guys, the Wikipedia values of case capacities of cartridges how are calculated? Are them good enough?

Thanks for the answers!

Bogdan


#2

Bogdan,

Volume of a cylinder is calculated as: (pi * dia. squared / 4) * length or (pi * rad. squared) * length.

To measure a case’s volume, it is common practice to weight the amount of water it holds and convert that to the equivalent volume of water in whatever units one desires.

Dave


#3

Yes Dave, that’s exactly what I have done, I squared half of the bullet diameter (radius) * pi * case length. And by measuring, I don’t own any tools required…


#4

QuickLoad software says that .32ACP holds @ 9.25grains of H2O to the brim or 0,601ccm of water.


#5

MarchHatchet,
from what you wrote I gather you overlooked the thickness of the base (primer etc) which for 7.65 Browning is about 4 mm, if the drawing I have is correct. Also, case walls increase considerably in thickness towards the base. Every maker uses his own internal dimensions, which are not standardized at all.
From the number Chickenthief gave you, subtract the volume which is taken up by the bullet inside the case.
For the latter you can use your formula: pi * radius^2 * seating depth.

The Lee manual, mentioned in the link you posted, lists the “useful” capacity. That is the case capacity minus the volume that is typically used by the seated bullet. Chickenthief cited the case capacity as 0.601 ccm and with a seated bullet, according to Lee, 0.45 ccm remain for the propellant charge.


#6

Ok Peelen, thanks for the answer. And one more thing, the case capacities that are found on Wikipedia pages are, as you mentioned above, with the bullet seated? And are the values of case capacities written on CIP or SAAMI data sheets? Thank you again!


#7

Sorry to have no better answer to offer, but neither SAAMI nor CIP define case volume. And my experience tells me not to trust data published on Wikipedia.