Chrono reading help? Shot over one for first time.

[cath8r]

Hey guys, wondering if I can pick the collective reloading brain here. First I'll give you the gun and load info then what is going on.

I had a rifle assembled by one of the gunsmiths here and I'm pretty pleased. Its exactly what I want for coyote hunting. Trued rem 700, McGowen 1/8 rot barrel cut to 22 1/2" chambered in .22-250. Bedded into a BDL walnut stock. Chambered to the Hornady 75gr Amax where I load the bullets to 2.565" OAL to just be into the lands.
My load is 75gr Amax over 35 grs of H 4350 and winchester primers. Zeroed the gun 200 yards and its under sub MOA. Maybe 1 1/2" groups but I have to get used to the rifle more as I'm getting called fliers that are opening the group up but the bullets are landing where the crosshairs are. I'm weighing each charge on my RCBS balance scale. Gun was broken in as per gunsmiths instruction and I've got about 25 shots through it so far.

Today is calm so I set up a 300 yard target and my chrono. First shot reads 3018 fps, 2nd reads 2987 fps and 3rd reads 2947fps.
#1 lands 2 1/2" low dead centre.
#2 lands 5" low dead centre
#3 lands 8" low and 6" right.
Started raining so I packed up. I know I still have to get used to this gun more and I'm not a guy that gets to shoot all the time. I know i'll get the groups to improve with work on me and my reloading technique. But the question is:

Is it normal to get readings to jump down like this on the chrono?

 

[Longwalker]

You're expecting too much if you think you can interpret a trend from three shots. Yes, it is normal for a "jump down" - or a jump up, or any other variation from shot to shot. Shoot a string of ten and that will tell you a lot more useful information about how variable your loads are. A string of five shots is the absolute minimum in you are trying to measure uniformity and not merely checking "average" speeds. If the load you have tested varies a lot, you should probably fine tune it with different charge weight, different powder or a different bullet. But you need to shoot enough to establish a trend.

 

[cath8r]

Thats about what I figured. I would have shot more had it not started raining. I just found it odd that the 3 shots in succesion all went down in speed. Almost 40 fps each shot. I'm gonna keep at it.

 

[rral22]

There is a level of "randomness" in reloading that everyone tries to eliminate in the hope it will improve accuracy, but it is impossible to wipe out completely. That means you must think about statistical facts like sample sizes, standard deviations, and averages and means, in order to understand what the numbers tell you - and what they don't prove at all.

The science of reloading (and it should be approached scientifically if you want to beat the factory stuff, because they do it scientifically) is lots of interesting fun.

 

[cath8r]

Thanks. Next chance I get I'm going to shoot 10 shots spaced apart from a cool barrel to see what I come up with. I'm going to dry fire alot at 300 yards to get the hang of shooting that far too.