11% antimony might be a bit higher than needed, depending on calibre and desired characteristics - meaning penetration and/or expansion.

Lyman's #46 manual lists a number of alloys suitable for casting bullets, from Monotype at 28 BHN to pure lead at 5 BHN.
BHN- meaning it's # placement on the brinel scale.
Lyman's #2 brinel is rather hard, at 15.

It is comprised of" 90% lead, 5% tin and 5% antimony.

1:1 mix of linotype (22BHN) and lead (5BHN) will yield an allow of 15 BHN.

Alloys with some arsenic, ie: American/Canadian lead shot, and non-zinc, non pure lead wheel weights which usually runs 9 to 12 BHN, respond well to heat treatement.
common
US wheelweights (non pure or zinc) usually are comprised of: 95.5% lead, .55 tin and 4 % antimony.

Tin/lead mixes, common with black powder ctg. shooters, in mixed from 10:1, to 30:1, do not respond to heat treatment. thus, a tin/lead mix can be used on a WW bullet as a soft nose, as it will not harden as the base will, if heat treated. Thus the base can be made up to about 32 BHN and penetrate like a solid, while the nose expands like a Nosler SP. Such a bullet, when driven by a slow powder and lubed with something like LBT Blue, can be driven up to 3,00fps without leading. I have personally run a .375 to 2,750fps with 270gr. GC bullets without no leading & 1 1/2" accuracy with cast bullets using heat treated WW and LBT blue.
Lyman's #2 alloy easily runs to 2,000fps in most rifles, with a good lube, of course.
The .458's and larger can use softer bullets for those speeds, allowing penetration and expansion. I've found 1:1 Pure and WW mix worked well in my .50 Sharps, .50RB and .45 cal. Sharps all the way to 2,000fps (RB). I kept the Sharps in below 1,850fps.