45 Load - large difference in velocity

I am loading 4.56 GB VV n310, Nosler 185 JHP, Winchester Primers, 1.20 OAL, 0.471 crimp.
I chronographed the load with case lenghts measured in 3 groups: 1.8855-.8875, .8875-.890 and >.890
I am getting velocity deviations of 111, 94, and 91 respectively with average velocities of 701, 706 and 711 respectively
This is a 13%-16% deviation - NOT GOOD!
I am using a Dillon square deal and the powder measure is very consistent as far as my testing indicates (and scales (both beam and electronic) that only go to 0.1 GN

Does anyone have any ideas why I am getting such poor consistency? or things I can try to get better results?

Thank you
Marc

How's it shoot?

You may want to tighten your crimp up some, try .4690 - .4695. The jacket bullets like to be hugged tightly! Everything else looks very close to my loads (I have never measured case length) and they run a STDEV of 16.79. Are you using mixed brass? Different wall thickness will vary your crimp, thus your change in velocity.

I shot some factory Remington loads today that ranged from 773 - 837 that surprised me!

sorry, I forgot to mention I am using all Federal brass (reusing from previous reloading, but all federal or all of the same type if using other mfgr when testing to minimize differences)

Steve - it shoots pretty well: 50 yds, a 6" delta from high to low (hence the velocity difference)
Joe - very surprising/disappointing for factory loads
I will be velocity testing some federal 185 match soon

I do not put a lot of value on bench resting and chronographing loads. It would be interesting to see if you could associate the high and lows to shot placement. I just have a hard time thinking that even 75fps would dramatically change POI.

In my testing today which was 100 shots on one target at 50 yards I had various bullets, brass and powder at velocities from 601 - 837 fps. all but 12 were in the black for a score of 888/1000. Bear in mind I was not trying to shoot groups, just get the velocity of the loads and not shoot the chronograph. I was searching for a specific combination to achieve 700 - 710 fps.

Does it shoot accurately and function in your gun? I have never chronographed a bullseye load. My brass is whatever I can get my hands on. I don't measure or segregate by case length and my crimp is just enough to remove the case mouth flare and this is checked by feel not measurement. Go shoot. A lot.

I'd suspect the chronograph technique. How far in front of the muzzle is the skyscreens? Maybe check it with some factory ammo.

Your crimp is too loose to get a consistent powder burn. A FMJ should be set at .467-.468 this is what all match grade factory ammo ive tested is crimped too.