Finally got a Chronograph!

[sawdustdad]

I don't know how I have lived without this thing. It is so cool. I picked one up in the LGS the other week, it's the RCBS bullet shaped thing. I tried it out yesterday--had it set up in front of a safe berm at home. I kept going back into the house and shop, finding another gun and load to test, had a blast. Clocked a half dozen loads in several different guns. Made up a notebook to record my findings. For the first time I actually know what is going on with my loads and can measure them for consistency with the SD function.

So now I know the Avg Velocity and the SD, as well as extreme spread.

What else interesting do you use your chrono for?

 

[Nick_C_S]

Ave Velocity and Extreme Spread are the two biggies.

In the pistol world:

How you use the data depends on your application. If you're loading for a Power Factor for competition, you need to do the calculations to find the minimum velocity for the bullet. Once you find the load that just achieves minimum velocity, then you want to find one just slightly higher that has a low SD. That's an over-simplification of the process, but it gets the point across.

For hot Self Defense rounds, you want to monitor velocities, while checking for pressure signs - or while staying within your comfort level, whatever the case may be. Usually, in a range of power levels, there will be one that shows a low SD - that is probably the best loading for that particular gun. Certain load levels tend to "settle down" compared to loadings on either side of it. Those are usually the keepers; and naturally, tend to be more accurate.

A lot of over-simplifying there.

Usually, when you gather chronograph data and crunch it, it raises more questions and prompts you to load up some more stuff for the chronograph I'm not sure the process ever ends

 

[wogpotter]

Load development.
Make 3 "batches" one "min" one "MAX" & one 1/2 way in between. For safety I usually check several books & pick the hottest "min" & the Coldest "MAX".

Then you can draw a a graph of "how many Gr of powder do I need to get "x" FPS? all I do is pick where on the sliding scale I start loading. Another way is to express it as "Each "x" Gr of powder for this exact load is "Y" FPS!
This is such a graph comparing different powders & bullet types.

(Image & data (C) Wogpotter 2009)
It saves a LOT of load workups.

 

[sawdustdad]

So wogpotter, I assume you are plotting avg velocities? Data looks surprisingly linear. Maybe over this small a range, that's to be expected. Very cool, Thanks for sharing.

Yes, Nick, there's a power factor rule for CAS, and I can check my loads for that, but I don't think anybody I've talked to is very concerned about it. Maybe above the club level it matters more... I was surprised my CAS loads averaged about 625fps, while I thought they should be closer to 750 based on the load manual.

The min power factor for CAS is 60, or equal to a 100g bullet at 600fps. Since I'm using 125g bullets and avg 625fps, I should be good.

 

[wogpotter]

Data looks surprisingly linear. Maybe over this small a range,

It is, that's the secret! The bottom is the minimum, the other horizontal lines are the various max data from manuals.

The solid lines the published data extrapolated from min to MAX. Dotted lines above MAX are theoretical only.

If you look carefully the dashed line is my actual firing data for the 165 Gr .30 cal Sierra GameKing HPBT. You can see where there are little deviations from the various makers data tables. That's one of the advantages also you can deduce that YOUR data is exactly how different from the factories.

Yes the velocities are my average of a 5-round group if I'm firing.
If I'm taking data from a manual to create a load there is no average yet, just published data.

 

[Mac Sidewinder]

I guess the best use of my chrono when I started reloading was to help me gain confidence in my reloading technique. If my loads were close to what the reloading manuals said I "felt" better. I could also tell which powders my reloading equipment "liked" and which they had a harder time keeping consistent throws. They are not a must but they sure help at times.

Mac