Huge Velocity Variance...?

[Seeking_Coyotes]

No idea what is going on... Been reloading about 12 - 15 years.

Getting 100 fps velocity delta between ten rounds I shot through the chrony! This was a ladder test load that was putting five inside an inch but tonight is the first time I took out the Chrony. Sig Sauer M400 Predator AR-15, US Optics MR-10 scope, etc.

Using a Rockchucker, CFE 223, Lyman digital scale, small rifle primers. 60 grain Nosler Vmax, mixed brass. Full length sizing (always). COAL within a thousands of an inch. What the heck could be causing this...what am I missing?

Anybody ever had this happen and diagnosis the culprit? These are huge swings in velocity and overall slower than I expected by about 200 fps.

[Seeking_Coyotes]

Here is the velocity data:
3027
3091
3064
2851
2965
2931
2996
2965
2902
2933
2961
2888
2966
2991
2986
2958

[Hippy]

My guess would be "mixed brass" as brass varies volume between manufactures

Jim

[Hog Patrol]

Can you try another chronograph? That may be the culprit.

[GrocMax]

Does factory ammo do OK?

Could be a gas and timing issue with the slow powder.

[SmokinJoe]

Might try a hotter primer, sometimes ball powders respond well to that. However, I don't remember CFE223 being particularly hard to ignite.

[ramos]

It may, or may not be the mixed brass. Until you eliminate that possibility, you will never know. In other words, I would start there and see what happens.

[TAJ45]

As was said, is the chrony wonky? It would seem that much variation would show up in group size. Or am I greatly mistaken?

[Bill K]

First I would load the same charge/bullet/etc in all the same brand/marked case's and see how they do. Could well be the issue. Then go from there, if you obtain the same results. Bill K

[Dean2]

If you have been loading 15 years and still use mixed brass then you are volume loading for spray and pray. No accuracy loader would ever think of doing this.

Your SD is wide, and your extreme spread is REALLY wide, but in rapid fire under 100 yards it won't make any difference. Th biggest issue you have is if you increase the charges to max book a number of those rounds will likely be quite a ways over the pressure limits. As it is you are loading light enough that the case differences shouldn't cause a problem. If you want to clean up your SC ES go the matched brass of the same weight.