Air pressure in case?

by Mike38 Thu 19 Sep 2019, 5:33 pm

Something very odd happened while reloading some .32 S&W Long with 98 grain hollow base wadcutter bullets a couple days ago. First, a little recent history. The bore on my pistol is .314, loading .314 diameter bullets. But the expander I was using only opened up the case to .312. So I'm swaging the soft wadcutter bullets when I pressed them in. I had a custom expander made to .315 and as deep as the wadcutter bullets, figuring "spring back" would give me .314. Well, the spring back part works, leaves me with a fit that allows seating the bullet with finger pressure, so I'm not swaging the bullet. But, when I insert the bullet, air pressure in the case pushes the bullet back up about half way. It must be a perfect fit that will hold air, yet allow me to push the bullet into the case by finger pressure only. During the crimping process, on 5 of 50 rounds, this trapped air pressure pushed the bullet up, and I have a too long overall length. I discarded these 5 bad rounds.

How do I stop this from happening? I'm thinking about putting the expander in a lathe and use 1000 grit sandpaper to bring the expander diameter down from .315 to .3145. Then with spring back, I should end up with .3135 which may be enough to hold the bullet in place long enough to crimp.

Your thoughts?

by Dcforman Thu 19 Sep 2019, 5:50 pm

Try expanding only about 85-90% of the bullet length. When you seat, the bottom 10% of the bullet will be swaged down a bit, but I'd bet this won't affect accuracy. The unexpanded portion of the brass should hold the bullet in place.

At least it's something to try.

Dave

by fc60 Thu 19 Sep 2019, 6:26 pm

Greetings,

Brings back memories of when I was loading 32 ACP bullets. They were "popping" back up from the trapped air pressure.

I selected a sizing die 0.001" smaller.

Cheers,

Dave

by DA/SA Thu 19 Sep 2019, 6:27 pm

Mike38 wrote:Something very odd happened while reloading some .32 S&W Long with 98 grain hollow base wadcutter bullets a couple days ago. First, a little recent history. The bore on my pistol is .314, loading .314 diameter bullets. But the expander I was using only opened up the case to .312. So I'm swaging the soft wadcutter bullets when I pressed them in.

Your thoughts?

Have you pulled some projectiles and measured above the skirt to confirm this?

Have you shot and compared targets with both expanders?

The object of HB projectiles is to conform to the barrel bore easily under pressure.

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