Perplexed by loads

[Joshm28]

Just a little background...I got into reloading about 2 years ago. I finally got around to buying a chronograph to check fps in order to order some Kenton Turrets. I tested 3 rifles, a Sig SHR970 300wm, a tikka 300 wm and my custom 6.5-284. All loads have been developed based on 100 yard group accuracy. The 300 loads shoot just under an inch and the 6.5 will shoot .25" if I do my part.

Now the question I have is in regards to the Extreme Spread and Standard Deviation of the loads. The Loads for the sig produced an ES of 38 and a SD of 19.3, the load for the Tikka was a little better with an ES of 23 and SD of 11.8. What surprised me the most was the 6.5, it produced an ES of 88 and SD of 31.9.

I use Lapua Brass for the 6.5 and run 48.5g of IMR4831. I manually weigh each charge on a digital scale and check throughout the process with a balance beam scale. Bullets are 140g SSTs, which was not my number 1 choice but they shoot so well I decided to just keep running them. What could be causing these higher numbers? My process seems to be working based on the other loads but this is perplexing.

Any help is greatly appreciated.

 

[g0rd0]

if you are getting accuracy like that with 88es I cant see a problem. What kind of accuracy are you getting with that load at 500 yards?

 

[Wyo7200]

What chronograph did you get and what was the weather like when you shot through it? Some overcast weather can effect those light dependent chronographs ability to read the bullet.

Lots of variables can be at play...

 

[RockyMtnMT]

I agree with the chrono giving possible errors. I have chased chrono readings around in circles too much. Then there is always the doubt that comes later. Is the speed accurate?

Finally got a magneto speed.

Steve

 

[FearNoWind]

I agree with the chrono giving possible errors. I have chased chrono readings around in circles too much. Then there is always the doubt that comes later. Is the speed accurate?

Finally got a magneto speed.

Steve

Me too ...................
Bought the Magnetospeed and never looked back. Love that little puppy ....

 

[Joshm28]

I'm using the Competition-Electronics-ProChrono-Digital-Chronograph. Weather was mostly sunny with temps in the mid 50s. I have not shot these loads at distance yet but like I said its under a half inch all day long at 100 and 1/2 that on MY good days.

 

[Engineering101]

Joshm28

That chrono is one of a handful that are decent so I suspect it is telling you the truth. A good way to find out is to stretch out to 600 yards or so. If the ES is really that bad you will have a relatively large vertical. If it holds the same MOA at long range that it does at 100 yards then there may be chrono issues. You can actually run the numbers using the velocities you already measured and predict what you would have gotten had you been shooting at 600 yards. Then go shoot at 600 yards and you will know what you are looking for. If you see the spread vertically that you predicted, you have more load work to do. I never work up loads at 100 yards for this very reason.