in2anity wrote:It's notably slower that AR2205, so just 100% fill should be safe. But it's important to keep density up. Would you agree Blade? Is there risk of SEE (considering the case would be completely filled with "too-slow")?
My understanding is slower-than-optimal burning powders that can safely be used for the cartridge based on if they will fill at least 80% case capacity, preferably 86% or more - even some compression is probably ok. To me, a neat 100% makes sense - just be prepared for poor velocities, big muzzle flashes and un-burned granules scattered everywhere...
No, SEE is not going to be a problem as you need as much powder as you can cram in there.
I'm experimenting with 9mm currently.
A full case of AR2206H is 12.5gn, or 9.5gn to the base of the bullet (I'm using Winchester 124gn Ball - I bought heaps of them).
I was doubting the chronograph due to lots of errors and cloud cover. But giving it some thought, I think they're in the ballpark. A 124gn bullet is roughly a third the weight of a 3/4oz shotgun load (328gn plus the wad, so around 365gn), and a low-recoil 3/4oz training load makes around 1100fps, but still has noticeable recoil. 9mm Para makes around 900-1000fps with 124gn bullets. So if I were making 900fps or so I would expect to feel some degree of recoil, which I'm not, at least nothing noticeable. My first test shots were fired with the gun one-handed at arms reach just to be safe.
8gn gives me around 300fps.
9.5gn gives me around 500fps.
No indication of pressures, and the soot around the case mouths would confirm they're quite low pressure loads. 8gn leaves some empty case volume, 9.5gn doesn't, it's not compressed yet but almost doubles the velocity. Next step is to compress it significantly, so I'll try 11gn next. I think I can get 12.5gn in and still be able to seat the bullet to 1.170", but it'll be heavily compressed. If we need more powder still I think I'll have to drill out the base of the bullet (also lightening the bullet and driving up the velocity requirement), and vibrate the powder charge to maybe fit a 14gn or 15gn charge in there.
To make Minor with 124gn bullets I need to make 1010fps out of my 175mm barrel. So, about double what I'm seeing from 9.5gn - it's not looking good. But it might be possible to get a practice load that will cycle a handgun at least. To make Major would need 1330fps which would probably require a liberal sprinkling of TNT in the powder

I know most of you guys are using cast bullets for IPSC, but I want to concentrate on whether this is achievable with a bullet that I know works already. If I can get the velocity we need from common rifle powder, then I can put some additional effort into casting a bullet that works with it. I don't want to waste time making a bullet that works only to discover that that we can't get it up to minimum velocity anyway.