has anyone had this happen????

[tony212]

We have been working up a load for a .270 win.  We are using Winchester cases, Federal 210 primers, 130 grain remington PSPCL, and IMR 4350 powder.  We worked from 52 grains to 53.5 grains.  At 53.5 we were getting 2930 FPS through the chrony.  Our goal was 2950 to 3000fps. We moved up to 54.5 grains and our average velocity went down to 2866 fps. Everything was the same except on our first few outings the skies were cloudy so we didn't use the skyscreens.  We had no errors and the Chrony seemed to work well.  On the last time out it was a sunny day and we used the screens.    Could using the skyscreens make the chrony read the velocity different?   And if it does which is the accurate one??  Has anyone else had this happened?
thanks
Tony212

[Questor]

Conditions do affect results, depending on the chrony and the angle at which you were shooting. If, for example, the first session was shot with the gun level and the second session had the gun pointing up or down several degrees, that could make a difference.  Also, some powders are sensitive to humidity and cases loaded in dry conditions can have a different velocity than cases loaded in humid conditions.  Also, if you used cases from a different lot, or a different lot of primers, that could do it too.

[Graybeard]

While not overly common it is NOT all that umcommon either when you pass the safety zone for your rifle.

When moving up and nearing max it is best to not move in one grain increments but in half grain. When you're reaching your gun's max it will some times show a reduced rather than linear increase in velocity. That's a real good time to stop and back up some. The next thing you know you might be seeing huge increases and blown guns. There are just no reliable visual pressure indicators and folks who think otherwise are kidding themselves. Sooner or later they'll blow a gun. Been there done that and don't plan to do it again.

GB

[New Hampshire]

What Graybeard refers to is what is commonly called "the law of diminishing returns."  Its when you reach a point that performance (and sometimes your safety) drops off with the more powder you add.  Remember, reloading manuals are just "guides."  They are not set in stone which is why they tell you to work up loads.  you've done good by using the chrony.  Its pointless to try and keep stuffing powder into a case just for the heck of it, especially when you start getting poorer and poorer results.
Brian M.