I've been loading for a number of years, mostly using Unique, and Hodgdon Universal, with a short flirtation with Bullseye. Fairly recently, I had a talk with one of the Speer people, asking about loads for use with their shot capsules. Their data recommends 5.5 gr. Unique in 38 Spl. brass. As it happens, that has been my go-to load for years, only in 357 Magnum brass...IPSC, plinking, etc.
I asked about using 4.5-5.0 gr. Unique, for perhaps better patterns out of my 4" revolver.
The tech said NO! and something about airspace in the cartridge causing problems. (?)
That's the first I had ever heard of airspace problems in a pistol cartridge, and I have used as little as 4.5 gr. Unique in 357 brass, behind 125, 150 and 158 gr. cast bullets with no problems so far. I can seat the shot capsules to the recommended overall length for .357...1.590 in., with no problems.
Except...there was a time I wanted to see how small a charge would get a boolit out of the muzzle, and 2.5 gr. Unique stuck it in the barrel. Why would I do that? Well...this article in a Gunzine suggested really low velocity loads were fun, and the scribe said he went as low as 2.2 gr Unique! That resulted in a little kid at the range asking his mom;"Why is that man hammering on his gun?"
Somebody please school me, what are the hazards, if any, of using the smaller loads of Unique (4.5-5.0 gr.) in 357 brass for shot capsule loads, and with cast boolits, too?
Thanx