CCI primers are more sensitive, easier to seat, and more compatible with progressive loading equipment than ever before. 209 primers are for field & target loads in all gauges. 209M is a true magnum primer designed for heavy charges of slow-burning propellants which makes the 209M a superb choice for waterfowl loads. 1000/bx.
Big Book Catalog, Issue:68, Page:545
Sinclair, Issue:5A, Page:117