[mec]

I got high spreads with WW magnum primers, 158 xtp and 13.5 2400. Went to 14.5 grain compressed load and still got high velocity spreads. Switched to STANDARD CCI primer and things got a lot better:

[mec]

the actual velocity of the magnum primed 14.5 grain load is 1282 I attempted to swap picturers and was stopped.

[Standing Wolf]

I've been happy with CCI primers for years, but have had mixed results with Winchester. I generally make up light target loads rather than loads like yours, but it's interesting to see someone else has encountered the same phenomenon.

Excellent presentation of data, by the way!

[mec]

same here- somebody else with the same experience. the only problem that shows up with the ccis is when you have a light spring. Hard to set them off.

[mec]

I got hold of some CCI 550 magnum primers and loaded from the same exact setup using virgin Starline Brass as before. the only change is the CCI Magnum primer.

This ninety caliber group is the smallest I've fired from the 6" gp
http://www.thehighroad.org/attachment.php?s=&postid=229986

[HerbG]

I've experienced the same velocity spread using 2400 regardless of the primer. A heavy crimp and minimum expanding of the case neck help reduce the spread. Like WW296, 2400 needs a good crimp and tight bullet/case fit.

[mec]

exactly, These were all put up in either vergin or once fired brass with strong crimp.

[357Man]

Interesting stuff. The latest Speer manual has a note in their .357 data about them retesting their loads with 2400 and switching from magnum primers to standard primers. They note they got much better consistency with the standard primers.
The Winchester Magnum is the hottest small pistol primer out there, hotter than some of the small rifle primers.