Pressure Question

[Johnch]

OK I know this just Wrong in so many ways

But it works ....and lowers my bar bill when others bet me I am full of it

Well I know 9 mm and 380 ACP are not the same
Also they have different load data and head size

But in a screw up (by me) loading 9 mm with a Dillon 550 press
I loaded some 380 ACP cases with 3.8 gr of HP 38 and a 125 gr cast bullet ....slightly less than the starting load for a 124 gr jacketed bullet
But at the same OAL as the 9 mm load I was loading

So to not waste anything I shot the loads in my Glock 22 ...Err 17 .... I switched barrels
I also shot some in the High Power

Worked just fine
Extracted

Not as good of a group
Just had a different POI


Not in any way plan on shooting a any more of this loading as the 380 ACP case has a slight bulge IMO due to the chamber size

BUT I was just wondering what kind of change there would be in the chamber pressure
As both of the cases were loaded to the same overall length
But as the 380 ACP case has less case volume

I would think the pressure would be slightly higher

Thanks
John

[Bazoo]

It wouldn't be much of a difference because the cases are so similar in size internally, and you were at a low level. I probably would have shot them too.

You could trim a 9mm case the same as a 380 case and measure their respective water capacities.

[Cole440]

As the same OAL i bet the pressure difference is negligent... I would've should them too haha

[BrutalAB]

I would bet you that pressures would actually be slightly lower.
The inside of a 9mm case tapers and rounds at the bottom, 380 cases are much more straighter giving them slightly more 'below the boolit' case capacity. (At least i think so without doing any measurements.)
At any rate the difference is likely negligible.