Load to keep .45 Colt subsonic in Rossi 92?

[LivewireBlanco]

Here's the deal, I have a Rossi 92 with a 20" barrel. I'm using 250 gr lead flat point bullets and Unique powder. I'm wanting to push it as fast as possible while still keeping it subsonic. I'm thinking 8.5 gr of Unique but I don't have a chrono. Am I close? Should I just keep loading hotter until the tell tail crack appears?

 

[rcmodel]

Chase the crack and don't look back!

Lyman #49 says 9.0 gives 1,157 out of a 16" winchester with #454190 mold design.
And 8.2 gives 1,101 with #452664 mold design.

BTW: The crack changes speed at different air temperature too.

rc

 

[LivewireBlanco]

Yeah I know that there are a lot of factors that go into determining the speed of sound but I'm just looking for something close without going over. Hopefully someone has some info that can help!

 

[TooManyToys]

Sounds like your pretty close with 8.5 gr.
Every gun /bullet combo will shoot a bit differenly, so its probably time to load up a few rounds above & below and chase the crack.

Good louck! Let us know what you find.