I have a carbine in 30-357 mag which was made by running the 300 blk reamer in short and cutting a rim.
I can get H4195 (adi Ar2207).
I’m wanting to load either fixed or breach seated with it.
It holds 1.4 grns I believe less than the 300 blk.
Anyone played with the blkout?
Rifle is a martini cadet and the twist is 1:8.
I’ve had success with fast pistol powders semi fixed seated like Martini Belgium does but they seem to be drying up here.
Any good heavy nose riding short base groove diameter bullets or others worth trying in this?
Here is a pic so you know it happened.
It’s mostly for fun shooting and not serious competition.
But it does shoot nice.
I don’t know what bullet to use for a couple of hundred yards sonic.
I have shot it a bit subsonic but haven’t got a wind cheating fool of a bullet to use in it yet.
Ideas / experience /suggestions welcome.
Thanks 
Bruce

H4198 is the fastest powder available here at the moment.
Otherwise I would be using a faster one.
Suppose I’m more worried if the unburnt kernels are going to do damage or not.
It will have to get me by for a while.
Thanks.

Well  tried 11 grns ar2207 with 180 pb #315 clone today.
At 50 yards showed promise.
I may have to make a blow tube to get rid of the powder kernels entering the martini’s action when extracting cases.
I tried single load ladder testing and at one stage it seamed to kick in.
I only went up to 14.2 grains and it went 1420 fps over a chrony.
I could pack in more powder but it seems that the powder maybe is getting kicked around by the primer and causing wild variances.
I may try some paper patched bullets but I will try a wad under the base on top of some filler and hope it might settle it some.
Looking around the house for a bit of tubing now.

I’m not sure it will like pb speeds at 1350 ish fps
I may try breach setting anyway.
At least I am fertilising the grass in front of the bench.
I wonder if a longer heavier bullet would help.
Bruce

1:8 twist
I use a 0.310" and "300 sizer that makes all bullets keep in the case neck when seated into the throat.
I may have extra case volume than normally sized bullets.
I was thinking the soft finger lubed bullets may contaminate the powder if I had to seat deeper.

Bruce