Winchester Supreme 7MMWSM 160GR Accubond 20rds
Winchester primers come in WSP, WLP, WSR, and WLR flavors – small pistol, large pistol, small rifle and large rifle. They use the same primer for standard and magnum loads, which in essence means they are all magnum primers, and they act that way on a chronograph, with larger standard deviation in velocity than I get with a standard primer from CCI.
My preference in primers for standard loads is CCI, and generally speaking in a good load I can get standard deviations in velocity in the high single digits or low teens, where the same load may have and SD of 25-30 with a Winchester primer.
I’ve had good luck using CCI primers. From what I understand CCI benchrest primers are usually easier to ignite than their regular, magnum and military style primers. And the military and magnum primers need a harder strike to ignite.
I had my best groups at 100 yards using CCI BR primers in my AR-15 in 5.56. However, I don’t recommend using them in an AR because they would be the ones most likely to slam fire.
Never had a misfire or slam fire with either the CCI #41 or BR in the AR. Remington Small Rifle Bench Primers #7-1/2 Box of 1000