Big velocity jumps on Chrony??

[imohunting]

I'm working up a load for a 300 win mag and had some big velocity jumps through the chrony. First string was 2852, 2840 then 3085. Next string with a grain up went 2962, 2925 then 3065. Stopped there. Had 3 different loads up to there and nothing unusual. I'm loading a 200 grn berger with fed 215 primer and retumbo powder. Is my chrony on the fritz? Haven't experienced this before. Thanks for any imput.

 

[Broz]

It could be that the unit was too close to the muzzle. I have found 18 feet to be a minimum on a magnum.

Jeff

 

[curiousaussie]

Not a tight necked chamber custom is it?

I experienced large velocity jumps and large pressure spikes and poor accuracy in a tight necked 22-243.

Once I neck turned to give a good 3 thou clearance then all problems disappeared and accuracy superb.

Matt

 

[imohunting]

Thanks for the help guys. I'll try putting that chrony out to 18 feet, had it around 12, probably way too close. See if that does it first.

 

[ecomeat]

What Chrony are you using ? I had similar problems with a .284 Win shooting over a Shooting Chrony Beta Master.
My problem went away when I smashed it to pieces as advised by many others with prior experience, and replaced it with a MagnetoSpeed.
The very slightest change in light (ie cloud,sun, wind causing tiny variations) saw my velocities fluctuate wildly, just like yours.
No such problem since I killed the Shooting Chony !lightbulb

 

[SavageShtr]

I second the magneto speed!! I also have two shooting chrony's and since I switched I don't have any issues.

 

[Nimrodmar10]

It might also be because of differences in neck tension. This could be caused by non-uniform loading or by brass that needs trimming. If the brass gets too long it can jam into the end of the chamber causing the case to crimp into the bullet, causing higher pressure and velocity. Just a thought.