.357 Mag 125 gr JSP load with AA#9

[devils4ever]

Hi all,

I'm using a new combination of powder and bullets for my .357 Magnum. I want some load recommendations for the combination of Sierra 125 gr JSP and Accurate Arms #9 powder. My Sierra manual shows a range of 15.5 gr to 17.9 gr for AA#9 and 125 gr bullets. However, when I look at the Western Powder website, I see a range of 14.1 gr to 15.6 gr for a Nosler JHP bullet and AA#9.

I am using the Sierra 125 gr bullets, but I've never seen such a discrepancy before. I've been reloading for years, but the maximum of one manual is the minimum in another. ARGH! I'm not looking for a super hot load, just a safe, mid-range load for target shooting.

 

[kcofohio]

with 2 different bullets, the seating depth will not be the same. And there is probably a difference in the bearing surface.

I'd go with Sierra's data and start low. Be safe!

 

[devils4ever]

I contacted Sierra and will let everyone know what their response is. Stay tuned.

 

[devils4ever]

Here's Sierra's response:

My book says the same thing yours does, 15.5 to 17.9 grains of AA#9 with a 125 grain JHC in a 357 Magnum Revolver.
Ours is not a closed pressure gun but a Colt Revolver with a cylinder gap which does have a bearing on the pressure levels.

So, what I think he is saying is there is a gap in a revolver that reduces the pressure somewhat. A "closed pressure gun" is a lever action rifle which has no gap and will have a higher pressure?

I think I might start at 15.0 grains to be safe and work up from there.