.357 Magnum Load Data Paradox?


October 26, 2010, 10:22 AM
I ran into a strange situation looking at my load data the other day and I am looking for any guidance or experience you might have.

I am loading Hornady 180 grain XTP into .357 Magnum, using Accurate No. 9 Powder. I haven't loaded any yet because of the following:

My Hornady 7th edition reloading book says: 9.3 start 10.5 max
My Accurate Powder reloading data says: 10.8 start 12.0 max

Both sets of data use WSPM primers, A No. 9 Powder, and Hornady 180 XTP bullets specifically.
(The Accurate data has the oal 1.585, Hornady at 1.590)

I called both companies today, I told them both the situation and Accurate said they stand behind their load data but I could start lower and that would be ok. Hornady said I shouldn't exceed their data, and I should work up the load.

I will be loading these for a GP100 if it matters.

Where to start? Trust the powder company or trust the bullet manufacturer?

If you enjoyed reading about ".357 Magnum Load Data Paradox?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!
October 26, 2010, 10:34 AM
Personally, I would trust the powder maker as they do pressure testing and it is THEIR product that can do the most damage if the data is incorrect. Start at the bottom and look for pressure signs and inch up accordingly

October 26, 2010, 12:23 PM
To further compound your confusion:
Lyman #49 says:
180 XTP - AA #9
11.2 Start - 12.5 MAX.

I would trust them too.

We know for a fact all companies didn't use the exact same test barrel on the same days atmosperic conditions so all three sets of data are correct.

You have reached a MAX load for your gun when cases become hard to extract.

But besides that, your best accuracy will probably come somewhere before either data sets MAX loads are reached.


October 26, 2010, 12:28 PM
I trust the powder company. They do all checks for you. Start low and work up.

October 26, 2010, 12:31 PM
This is at the essence of reloading. Extrapolation has proved invaluable. I too tend to favor the powder company's numbers...

October 26, 2010, 01:43 PM
More info from Midway's .357 LoadMap series.
Accurate #9 powder---WSPMagnum primer---Win case--10" universal receiver
1.570" as tested-- Hornady 180XTP-HP
Midway shows pressures, has a dotted line and says use extreme caution loading above the dotted line and has colors on the chart and says to use caution loading in the yellow or red zone. Yellow is just below the dotted line with red above it. Won't list all the data but will give the range of data.
start AA#9---8.7 grains-25900 psi-968fps
9.9---33100--1088 This is the last load under the USE CAUTION going higher
Just for your info, recommended maximum pressure is 35000 psi and in the LoadMap it lists a load of AA#9 of 10.2 grains giving 35000 psi at 1119 fps. This is with the above components and in their test. Use this info for comparison only. Doesn't look like with this data that to get another 31 feet per second that it would be worth it to increase charges to maximum levels. Notice the velocity listed goes up 20 fps with each 0.2 grains and pressures up 1200 psi. ???? Just some more data for comparison.
Also, Accurate Arms Manual #1 lists 10.5 grains at 1003 fps and a maximum of 11.7 at 1140 fps and 35000 psi. Overall length tested at 1.575" using CCI 500 standard primers and Hornady case in a 8 3/8" barreled S&W K-38

October 27, 2010, 01:46 AM
I usually trust the powder company too BUT, when the bullet company loads their bullet and they reach the Max charge they are usually correct. Because there are so many different bullets out there these days with all different lengths I would go with the bullet company. If you reach the Max listed by the bullet company and you aren't achieving the desired velocity and there are no signs of excessive pressure you can probably go higher with the charge. This is just my opinion, you do what you think is safe...

October 27, 2010, 08:25 AM
Load 3 rounds at 9.3gr and work up from there.

October 27, 2010, 08:51 AM
When this situation happens to me, I usually start somewhere in the middle of the most conservative data (in this case, probably 9.9gr of AA #9), and chonograph the results to see where I am in reality. I'd also consult QuickLOAD to forecast what the load should do in the barrel length I'm using for load development. All these things working together help me develop good, efficient loads that don't overstress my weapons.

October 27, 2010, 08:01 PM
I have loaded 180 XTPs with 11.5g of AA #9, WSPM primers, and a heavy roll crimp with no issues at all out of my smith (used lyman data). Very accurate too. And they hit like a freight train! Whitetail didnt take a step! I plan on working up to 12.5g to see what happens. 11.5g seems to work great, so I may not mess with it. You will like #9. I really like #9.

If you enjoyed reading about ".357 Magnum Load Data Paradox?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!