The purpose of tin in a bullet alloy is twofold. One, it makes the alloy flow better when liquified and that helps it take up the small crisp details of the mold when solidified. Two, it to an extent toughens the metal somewhat.
The primary hardening agents in bullet alloy are antimony and arsenic. Small amounts of arsenic will make heat treating more efficient.
Anything more than 2% tin in an alloy is totally unnecessary and an expense with no gain. In fact, as long as your molds will allow it, straight clip wheel weight alloy (with maybe a max of around 0.5% tin in my experience) may cast just fine and produce a good bullet.
With regard to 'virgin' alloy- just what the heck does it mean? That this batch of lead was mined and the ore was smelted and it was never touched by human hands in the meantime? To be frank, most sources for lead are from scrap recovery. The element Pb doesn't break down except to oxidize or combine with other elements, when smelted and purified it doesn't matter how many times previously it has been molded into something. The steel in your automobile ('Virgin'?) has been who knows how many things in the past. Smelting processes can remove contaminant metals by breaking down and removing the impurities to result in pure lead.
'Certified' alloys means only that the alloy has been tested and found to contain a specific blend of metals and a minimal allowable level of certain 'contaminants' such as copper, zinc, calcium, etc. There is an industry specification for purity standards for refining smelted alloys. Assuming that the metal is purchased from a respectable foundry, and the specification for the alloy is given to conform to the standard, it will be an acceptable alloy for bullet making.
All 'certification' means is that a sample of the pour was tested by the lab and found to conform to the industry specifications for the type of alloy ordered.
So words like "Virgin Alloy" and "Certified Metal" are really just about as useful as "Spring Water" or "Jumbo Shrimp". They are great feel-good advertising words but really don't mean a thing in and of themselves.
If you want to see the writeup of the process, here's a company in India which gives a general description of their process.
http://www.gravitaindia.com/
In my experience most casters make bullets too hard. For higher velocity bullets such as the Magnums (1400 fps or thereabouts) you need maybe 18bhn max and a properly sized and lubed bullet. Superhard alloys of 20+bhn really aren't the solution to leading.
The 327 has enough case capacity that you can use a 32-20 rifle bullet as long as you work up the load from a mid-range starting point. Sizing around .313-.314 will work just fine.
I cast the Lee 311-93-1R and it drops about .314" with my alloy of scrap. I load it in everything from 32 auto, 32 short, long and H&R Mag and 7.62 Nagant. It works just fine in everything and I only use ALOX tumble-lube.
As far as brass goes- good luck finding some. I sell thousands of pounds of brass and all I've ever found was about 150 of them over a couple years. They sold quick, too.
