Thank you very much for taking the time to contact us here at Winchester Ammunition. We are always glad to hear from our many friends and customers who share in the shooting sport.
WSP is a Small Pistol Primer. WSPM is a Small MAGNUM Pistol primer. They are not the same.
For current Winchester Reloading data go to
http://www.wwpowder.com
Thank you again for contacting us here at Winchester Ammunition. If you should require additional information, do not hesitate to contact us.
Sincerely,
Winchester Technical Department