Mike TX, when you say "close enough" do you mean that for gas check v no gas check and such that the .08ish percentage's?
I am looking at casting for .357 in my Rossi M92. I have a very basic understanding of casting and am trying to learn more.
thanks for the info!
Well I'm not real sure I understand just what your asking, but heck that never stopped me from trying to answer.
A couple of things on casting, velocity, pressure, and hardness.
First off once you start to shove lead down your barrel without the jacket on it, it becomes a balancing act so to speak. Your matching the bullets to the bore, the velocity and pressure to the alloy, and the hardness to all of the above.
It isn't real difficult, you simply have to look at it somewhat sideways compared to shooting jacketed bullets. With them you start at one point and move on to another with your powder charge. Nothing really changes that much except the pressure behind the bullet. Where as with cast, not only does the pressure effect the velocity, but it also can play havoc on the bullet as it get slammed into the rifling. Too soft and it skids to a start. Too hard and likewise. Sort of like three bowls of porridge. You want the one that's just right.
Luckily there have been many tons of lead flung downrange ahead of you and I so it is a LOT easier nowadays to figure it all out. Just going on what I have learned, if your wanting to load to run int he magnum class loads, you are going to need an alloy somewhere in the 12-15 BHN range for your rifle, possibly a touch more but not a whole lot. Also it can be a plain based or it can be a gas check if you want a bit of insurance from leading. That is not to say it will eliminate it entirely, but greatly reduce the chances and severity.
Also the lube which you use will go a LONG ways in both helping to prevent it from starting and keeping it from building up.
If you will take the time and spend a few hours reading through some of or more of what is posted over at this site, it will answer just about any questions you might have.
LASC - Index to all Articles
While your there pay special attention to the listings by Glen Fryxell as well as the "Cast Bullet Notes".
I spent nearly a year and half reading, taking notes, printing stuff out, and saving a ton of it to my PC for reference. Then I started asking questions, and getting things together to start pouring my own. Once I hit the ground though I was off to the races. I've been loading my own ammo for right at 40 years, but I started very young under a VERY watchful eye. That said I have only been pouring my own bullets for about 2 years now. In those two years however I have not only learned a lot, but I have put a lot of what I learned into practice. Quite a bit was gathered from the above site, and another good bit was from over on Castboolits. It wasn't overly hard for me to put it together once I got it straight in my head, but believe me I am still learning something new with each new mold or alloy.
My best advice is to either locate a good source of lead first and gather up a bunch of it. Or if that isn't an option start looking for it in the classifieds. Look for folks who have sold before and have repeat customers, or have at least been around a while. Also try and stick with the basic types of lead like wheel weights, or pure. You will also need to locate some type of tin, whether it be solder or rounding up pewter at discount places and such. It will come in handy. If none of those are options you can purchase certified alloy from Rotometals, and know for a fact what your getting.
Also as I mentioned above if you will look for that calculator over on Castboolits, it is simply a spreadsheet, but it will help you get your known alloy softened, or hardened up with a pretty close and pretty easily repeatable formula that will also give you an approximate BHN of what it will end up as. Like I mentioned above, it might not be exact down to the last digit, but it is close enough to get you in the ball park and shooting with an alloy that you can easily replicate once you blend it up.