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Don't increase your loads over book until you determine some things: How much taper crimp are you putting on? If you use an accurate micrometer, you should mike a case, run it into the t. c. die and be able to read .002" reduction in mouth diameter. This is average. Some reloaders go a thousandth more on lead bullets.
Find somebody who has a well proven out load (one that has been chronographed) or buy a box or fmj rounds that will give you a place to start checking your chrony. If it is reading right on the 835 or whatever the velocity has proved out on another chrono or factory velocity on a lot of ammo, you know where to begin. A very small variation in screen distance makes a big difference.
It is best to check your chrony against another chronograph of proven accuracy, if you can persuade some kind handloader to set up on the next bench.
Once you know what the problem is, you can begin experimenting to solve it.
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