Can changing seating depth change chrono sd?

[LynnJr]

KingFamous
The chronograph will tell you were the node is but it might take more than one trip to the range to find it.
When using a chronograph to find the node you ignore the accuracy because you have to concentrate on getting your shots downrange in an even increment of time regardless of the conditions.

Here is an example of what your looking for.This is only an example not actual numbers.All extreme spreads will be for evenly spaced 3 shot strings.The guns barrel should be be clean and dry then 4-5 fouling shots should be taken to even out the barrels velocity.

2650 fps extreme spread 89 fps.
2690 fps extreme spread 73 fps.
2730 fps extreme spread 57 fps.
2770 fps extreme spread 38 fps.
2800 fps extreme spread 21 fps.
2845 fps extreme spread 45 fps.
2910 fps extreme spread 98 fps.

In this example the node will be near the 2800 fps load.As you incrementally increase your powder charge your extreme spreads will shrink as you approach a node and they will increase as you leave a node or have what looks like a waist or hour glass shape if plotted out.

You can then go back and change your starting powder charge and repeat your test using the same increments and this will tell you if your centered up or off to one side of the node.

If you hit the node and your extreme spreads are too high this is when you would do a primer swap.

Primers will change your extreme spreads dramatically and at $5 a 100 they are the cheapest component in your reloading arsenal for accuracy.

Don't worry about group size when chronographing and concentrate on getting the shots off in a nice even spacing.If you let a round sit in a hot chamber it will have a higher velocity throwing off your extreme spread and your standard deviation.

This is why most long time shooters will ignore chronograph numbers unless they actually know the person doing the testing.

While your at the range shoot 3 shots spaced at 30 seconds apart then place the 4th round immediately in the chamber and wait 60 seconds before pulling the trigger.Your 4th round will be 50-125 fps faster than your first 3 rounds if your close to a node.If your not close to a node the 4th round may get lost in the extreme spread if it is large.

[BLR81]

What's the standard deviation of a Chronograph? Are they that accurate? You hear all the time about crazy readings related to the light source.

Plus what is the vertical difference at 500 or 1000 yds of a 2800fps 308 vs. a 2820 fps 308 muzzle velocity out of the same rifle.

It seems like this is way beyond the accuracy needs of the average marksmen. We're not trying to land a rocket ship on a moving asteroid. And, anything other than long distance, the additional drop will be insignificant compared to wind or markmanship skills.

[CK_32]

Yes it will change MV and pressures.


Also know that even high end chrono's can be off to 20fps from actual MV. Reason most that the average and pop it in cause it's about.