I have a GP100 .357 in 6" and not sure which powders and primer to reach true mag velocities (match Buffalo Bore):

XTP bullets:
125 gr 1675-1700fps
158 gr 1450-1500 fps
180gr 1325-1360fps

I have the following powders but not sure if these will get me there:
Tightgroup
Longshot
Blue Dot
LIL'Gun
AA# 9

If you get the chance look at the Hodgdon data they offer it is good stuff and still includes the pressure values for their published loads.

Here is some Alliant 2006 data

Your listed powders-burn rate applicable for 357M full power loads
-Tightgroup-way too fast to use
-Longshot-slightly too fast
-Blue Dot-of the powders you listed probably the best
-Lil'Gun-too slow
-AA#9-too slow

I have to pick up some primers so I'll pick up some 4227.

I was planning on starting with 9 grains of BD and the 158 gr XTP and going from there.

Thanks for the input

4227 is a little too slow burn rate to attain the velocities you want,you'd probably have to use highly compressed loads. probably also,with 4227,you'll need a very heavy crimp to assure completely burning all the powder.

You will want a good crimp rolled into the cannelure of the bullet...Because that is why they have a cannelure is to allow the rolled crimp a place to fold into and secure the bullet...  The slower powders need secure crimps to allow for a full ignition.

Did you check out the .357 Magnum sheets?

All the best and worst in every weight. You should find something there to set your hair on fire 

https://docs.google.com/spreadsheets/d/12cjblt0pDB-csBqvoDoCLQH_SLRlUNLHkBVDxge1O2k/edit#gid=4

I got to sorting through my brass and found that I only have 50 pieces (300 .38 special) of .357 mag brass so I placed an order with Starline.

Once I receive the new brass, I'll start working on load development and post up my results.

I greatly appreciate the input all.

Ruger .357 , GP100, 6" Model 1707

I'm reaching the velocities in the Lyman #49 manual. However, I'm finding unburnt powder on the bench and on top of my chrony so I'm guessing that I need a tighter roll crimp.

Note: I matched my crimp (mine actually looked more consistent) to some Hornady factory loads.

No signs of pressure

Bullet: Hornady 158 gr XTP HP
Case: Starline 1.285"
Primer: WSPM
Powder: Blue Dot 9.0 grains
O.A.L: 1.590"
Velocities: Average 977 fps
Five shot Group size at 25yards: 1.25"
.........................................................................
No signs of pressure

Bullet: Hornady 158 gr XTP HP
Case: Starline 1.285"
Primer: WSPM
Powder: Blue Dot 9.5 grains
O.A.L: 1.590"
Velocities: Average 1057 fps
Five shot group size at 25yards: 1.25"
..........................................................
No signs of pressure

Bullet: Hornady 158 gr XTP HP
Case: Starline 1.285"
Primer: WSPM
Powder: Blue Dot 10 grains
O.A.L: 1.590"
Velocities: N/A
Five shot group size at 25yards: 1.35"
..........................................................................
No signs of pressure

Bullet: Hornady 158 gr XTP HP
Case: Starline 1.285"
Primer: WSPM
Powder: Blue Dot 10.5 grains
O.A.L: 1.590"
Velocities: Average 1185 fps
Five shot group size at 25yards: 4 @ 3/4" & 1 flier 1.50"

Note: When I started seeing unburnt powder and extreme velocity spread of 110 FPS

Yes a good crimp is needed but with Blue Dot you need a saturated loading...
My personal loading would scare some, I suppose...I have shot these at 11.5 grains

Lyman 358429 Keith Style SWC 165 grain
Caliber – 357 Magnum
Powder- BLUE DOT 10.5grs
Case – Mixed
Primer – CCI  550
COL – 1.620"   Sized .358"
Velocity – 1280 – feet/per sec  6" Barrel

Speer #9 shows the 158 grain JHP and JSP being used with Blue Dot  Ruger Security Six 6"  1:18.75" twist
11.0 @ 1149 fps
12.0 @ 1264 fps

Speer #10 shows the 158 grain JHP and JSP being used with Blue Dot  Ruger Security Six 6"
12.0 @ 1231 fps
13.0 @ 1328 fps

Speer #11 shows the 158 grain JHP and JSP being used with Blue Dot  Ruger Security Six 6"
11.0 @ 1185 fps
13.0 @ 1349 fps

This is the Speer 180Gr Silhouette gas checked I load these with 11.0 grains of Blue Dot here is my results...
357mag RCBS 180gr Gas Check Silhouette COL – 1.660" (loaded i the normal cannelure)
Bullet is 0.8330" long  (will not fit some cylinders loaded in the normal cannelure)
Inside the case is 0.4600"
Outside the case  0.3730"


Velocity 1320 feet/per sec my S&W Mod 19 6" 1:18.75" twist
Intercooler's Ruger 4" GP100 @ 1237, 1234. Average = 1235.5 FPS/ 610 LBS.

I went to a Redding profile die and opened the flash hole .001". All my unburnt powder issues went away which improved the ES and SD (10-12).

After trial and error with various powders, OAL, primers, etc; I settled on the following load for hunting (for now):

Bullet: Hornady 158 gr XTP HP
Case: Starline 1.285"
Primer: WSPM
Powder: 300-MP 20.5 grains
O.A.L: 1.575"
Velocities: Average 1626 fps
Five shot group size at 25yards: 5 @ 3/4"

Note: Started to see some pressure signs.

1.48" group at 50yds.





Cast my first .357 Magnum boolits using clip on wheel weights mixed with 2% tin. The mold is a Lee six cavity .358" 158grain SWC.



Air cooled boolits have a BHN of 13.4 and the water dropped (cooled) have a BHN of 19.3 after 7days.

I powder coated the boolits using Eastwood Ford light blue powder coat baked in a toaster oven at 400 degrees for 20minutes.

Note: All boolits had to be resized to .358" because the powder coating added .003-.005"




Powder coating hammer smash test to see if the coating would flake/peel:




Now time to start working up target loads for my GP100.

Wow, went from "normal-ish" 357 watered down loads to a 927 ft lb monster load!  Awesome!  I'm starting to really like 300mp, it seems to get better once you get into the heavy for caliber bullets (180+ in 357, 300+ in 44, 340+ in 454) high resistance bullets it begins to get happy.  More velocity and less pressure than h110 or lil gun.    I learned a heavy crimp is needed to get it to burn completely as well, much more so than h110.

I was never able to achieve those velocities in a revolver with jacketed bullets without pressure signs.  I have pushed cast bullets to 1450 fps. and they shoot really good.  W296 has been the best powder for me in a 357 with all bullet weights down to 125 grains.

I took this 11 point whitetail last month with a Dan Wesson 357 using a 158 grain Hornady JFP traveling at 1330 fps. from a 8" barrel.



I recovered the bullet in the offside shoulder.  It weighed 140 grains.

Quote from: TXCOONDOG on October 17 2016 05:38:52 PM MDT
I went to a Redding profile die and opened the flash hole .001". All my unburnt powder issues went away which improved the ES and SD (10-12).

After trial and error with various powders, OAL, primers, etc; I settled on the following load for hunting (for now):

Bullet: Hornady 158 gr XTP HP
Case: Starline 1.285"
Primer: WSPM
Powder: 300-MP 20.5 grains
O.A.L: 1.575"
Velocities: Average 1626 fps
Five shot group size at 25yards: 5 @ 3/4"

Now time to start working up target loads for my GP100.

I bought some 300-MP a while back and haven't tried it yet.  I will have to load some 158's with it to try in my Dan Wesson.  Thanks for the report.

My old go to powder was Winchester 296. But after Obozo got elected and caused the powder shortages I had been forced to use Unique or Blue Dot since I had stocks of both of them. I finally did get an 8 pound jug of the Winchester so I am back to using it.