I use 750, 650 and 400 all on the same test cases. The 750 goes on the neck and to the junction of where the shoulder meets the body. The 650 goes from mid shoulder to about 1/2" below the edge of the shoudler, and the 400 goes from the head to about three quarters up the body.

Using a Bench Source annealer w/dual tourches 22-250 cases take 3.6 - 3.7 seconds, 6mm Rem/ 6mmAI take 3.4, and 6mm Coyote (wildcat from a 6.5x47) takes 3.6-3.7 seconds. The blue pencil thin flame is about 3/4" away from the cartridge neck/shoulder area on both tourches.

The 750 is melted down the neck and about 1/2 way down the shoulder, the 650 starts where the 750 left off and is melted from mid shoulder to about a eight of an inch down the body and the 400 might have just started to burn where it takes over for the 650 which leaves about 80% of the remaining case wall untouched by any damaging heat.