GG,
How about you give us a more specific example of how one of your load charts might work, for example: sweet spot at 75 deg at 12noon( x amount of powder= y velocity fps),temp goes up to 85 deg at 2:00( what adjustments would you make and what results would you expect). Following morning 60 deg,etc. Are you trying to maintain a specific velocity throughout the day and thus stay in tune? If you weigh charges do you increase/ decrease weight to sustain a given velocity ?
You seem convinced that your program works and I would like to try it.
Thanks,
Joel
I'll sure try to explain it as best I can Joel. It is really similar, if not exactly the same as the load tables that Jerry SHaeffer outlined in his articles he penned for precision shooting and were then compiled into the Benchrest SHooting Primer book only he graphed H322 and I graphed out N133.
So the process is quite simple once you have a chronograph, a thermometer, and a notebook. The only difficult part (and it's really not that hard) is to be able to set up everything in a place that will let you shoot uninterrupted all day long and that has large temp swings from morning to afternoon. Of course, you can have little temp swings and still conduct the testing but your graph (or chart) will only contain as much data as you have in temperature variation.
The charting process begins with setting up a 100 or 200 yard target (I think 200 yards will put the load under a little more of a magnifying glass but 100 yards still works fine), and then shooting several loads to find the most accurate at that particular time. Then it is just a matter of writing down what the velocity was of that best load and then "mapping" it as the day gets warmer. You will see that to maintain that velocity, a certain amount of powder will have to be taken out of the load whether it be weighed or just thrown for volume. I have found that for every 10-15 degrees of temperature increase, the charge must be reduced about .3 grains which is roughly 30 fps with my current lot of N133 (other lots vary). Therefore, you can make a grid with temp on one side and velocity on the other and draw a line where you sweet spot is just like Jerry's diagram. Or you can just remember a starting temp and calculate what the charge needs to be based on the factors.
Now this seems to work in 90% of the barrels I've loaded for. However, there have been several barrels I've seen that didn't need a certain velocity but rather, they wanted a certain amount of powder in the case. Perhaps this is another form of a "hummer" barrel because it sure makes loading easy! You just simply have to stuff "x" amount of powder in the case and use it all day everyday. If you get one of these, HOLD ONTO IT for the big matches!
And if you want to take your chrono session one step further, you can load up a load ladder in .3 grain increments and watch the standard deviations fluctuate. If your particular lot of powder had large deviations each side of the best shooting load, then you will have to monitor the temp swings very carefully. If your load "window" is wide (meaning the deviations stay low on each side of the most accurate load) then your gun will afford you a little more slack as far as tweeking the load as the day goes on. But, there will still come a point no matter how wide your window is that your gun simply will not shoot up to expectations anymore and the charge must be altered. And sometimes you might just get lucky. For whatever reason, with the bullets and brass and gun that I'm using right now, I can actually feel a difference in my bolt lift when I've gone over the accuracy point. I'm not talking about the "pressure is too much" point. It is still very mild as far as pressure is concernced but I can feel when I've got too much powder in the case for the load to be shooting accurately. When I feel this, I'm approaching 3300 fps and I know I've got to be down around 3240 for this barrel to shoot.
On a side note, velocity is proportional to pressure and there are ways to change pressure without adding powder. But you will never know what they are or how to manipulate them without a chronograph. So it becomes a very useful tool in my mind and you will never see me sneer at someone for putting up a chronograph.
