Win vs FC Brass

[mwf008]

I did a full work up for my CA Mesa 7mm RM. In testing, I found a good .5 MOA load. First used the OCW method for POI then tightened up the groups with seating depth using bergers VLD method (shooting 168 VLD Hunters). All testing was done with Winchester once fired. Loaded up 20 rounds of my new load to chrono today and the groups opened up significantly. The new load is now shooting about 1.5-2 MOA. The only difference was I had a small lot of once fired Federal that was processed and primed so I used that instead of the Win. Assuming the rings are tight and its not the rifle, can brass make that big of a difference? It was all processed the same way. I thought the while point of the OCW method was to prevent these variables from making big differences like this? Chrono data with 10 rounds was ES-47 and SD-13. Its been about 150 rounds since a barrel cleaning so I'm going to try that first, I'm just not convinced thats what it is since the last range trip was well below 1 MOA. In fact none of the groups in the entire testing were any worse than this. Thanks for any thoughts y'all might have!

 

[tdhanses]

Imo, yes, different case capacity etc equals different pressures. Same goes for using different primers, consistency is key.

 

[JimGa]

In 308, Winchester has greater capacity than Federal, so I'd assume 7 mag would be the same. Yes, changing brass with different capacity can make a big difference. A chrony would show you the velocity difference between them.