7WSM Superformance Starting Load ??

[Sled2live]

I wanted to try some Hodgdon Superformance powder with some swift sirrocco II 150 gr bullets in my 7WSM, but am having trouble guessing a starting load. Checking out the load data for the 300WSM and 150 gr bullets the hodgdon site shows a starting load of 67 gr of superformance maxing out at 74 grs. I figured that I could start the same place for the 7WSM since their case capacities were similar (the 7WSM about 1 gr larger).

Now the confusing part. I looked at other direct weight for powder charges between the two cartridges (i.e. 150 gr bullet and H4350 and H414) and see that the 7WSM starts quite a few grains below the 300 WSM and in some cases max loads are reached in the 7WSM before the beginning loads for the 300WSM. That doesn't make sense to me. It looks like they load the 7WSM to 61K pressure wise and the 300WSM to 63K...but doesnt explain why the starting charges are so much lower in similar capacity cartridges.

Has anybody come up with a safe starting load for superformance in their 7WSM. Possibly someone could run QuickLOAD and give me a starting point for 150 gr sirrocco IIs and superformance.

I am open to all advice.

Thanks
Scott

 

[Sled2live]

So is superformance powder not in any version of QuickLOAD?

 

[wboggs]

Your bore is smaller than the .300 and with an identical case capacity so loads for the same weight bullet of 150 grs will be less in the 7mm. I use 72 grs in my .300WSM with the Barnes 150 for almost 3300fps and it is a pretty hot load. Start well below the .300 loads in your 7mm.