Question about pressures

dws1117 · Post by **dws1117** » Tue Sep 04, 2007 10:40 pm

This is basic information that I should know, but I don't. For example, if I load a .45ACP case with a 200gr lswc, 4.1 grains of Clays, and an OAL of 1.250 would the pressure increase or decrease if I were to shorten the OAL to say 1.225?

Thane · Post by **Thane** » Wed Sep 05, 2007 2:22 am

Pressures would, indeed, increase. You're burning the same amount of powder in a smaller space, which leads to greater force per square inch.

The amount that pressures would increase is something I don't know. Keep your handloads at or above the minimum overall length, and you'll be fine. The .45 ACP is a "relatively low pressure cartridge" anyway.

phddan · Post by **phddan** » Wed Sep 05, 2007 6:14 am

Dan

Houston1944 · Post by **Houston1944** » Wed Sep 05, 2007 9:49 am

The 9mm and 45acp are fairly forgiving calibers relative to OAL. You can adjust the oal on these without a lot of concern about getting into dangerous pressure spikes. The one you must be very careful about is the 40 S&W. The 40 caliber can have dangerous pressure spikes with even a small amount of decrease in the volume under the bullet.

Remember it is the space under the bullet that determines the pressure. If you are loading the 40 with a different shape bullet than the spec you are using then the oal is not the controlling dimension since the bullets may be different lengths.

mcub · Post by **mcub** » Wed Sep 05, 2007 10:29 am

If your are not loading to ward the maximums you have some room to work with. I load at, and only at the starting levels so my errors and variations in the cases are not a major concern. The closer to the max you get the greater the need to match the load data perfectly.

I'm wondering, why do you want to shorten the lenght??

mcub · Post by **mcub** » Wed Sep 05, 2007 10:35 am

Also, remember that when you change overall length, or case length, if youâ€™re trimming, you are affecting volume, not length.

Remember volume involves cubic equations so what would be a tiny change in length, can have a much greater effect than you think. This is why Over all length is in 1/1000 of inches.