Thread: 357 mag subsonic reloading data

Originally Posted by Muddyundy

Definitely I always work down.
A glance at X700 data has a start of 3.4gr for LSWC for 867fps in a 10” barrel. Could be a contender.
ADI shows 6.5gr AP70 in 18” barrel using LSWC at 1350fps and 5.8gr behind a 158xtp for 1059fps is minimum load. I have tried 5.8gr behind SWCHP and found it to be faster than speed of sound. Worked back from there and ended up at 5.5gr. Here is where the ES opened up and I’m below 45% case capacity. Shock horror I know but was rolling between 950-1100fps. I stopped there.
I have read stuff in the past about flash hole opening or changing primers.


As I say, just checking to see if anyone else has been here and done that and whether they had some good results.
After a quick ph around today, no-one seems to have any Trailboss and don’t know when it will be around again.

You are not going to get flash over or S.E.E in a pistol cartridge; do not open flash holes in any case all it does is stuff the case,
The reason your ES open up is the pressure drop below its optimal level go to a faster powder 700X is still a good choice velocity
wil be higher as there is no cylinder gape to bleed off pressure,
Trail Boss is probably not that much use in the .357 Mag any of the fast pistol and shotgun powders will do and are easier to find,
Hornady list 7 powders with start load velocities of 1000fps with their 180 grain XTP in a Rossi 92 16" barrel
If you are interested there is One box left in stock at Steve Wholesale.