Major loads arnt major anymore! Why?

[nikdanja]

5.7 grains got me around 930 FPS with a 180gr bullet back in August for Area 8 and again in may for a sectional match. Now that same load is averaging 910 FPS with the same bulllet. I know the cold negatively affects bullets but that seems like a lot. 

 

This is the first time if ever shot a fall uspsa match so I had to reason to track this. Is this normal? 

 

Im using a Win. WSF pushing a 180 extreme bullet. 

[L9X25]

Different lot of powder?

[caspian guy]

I don't recall if wsf is temperature sensitive.   I know that winchester super target is. Thats what a 2% drop? Temperature sensitivity or lot to lot variation could easily explain that... or even different light conditions on your chrono.

 

 

Edited November 3, 2017 by caspian guy

[Hi-Power Jack]

20 FPS is a small difference - if you fired 20 of each cartridge, you'd probably range more than 20 FPS

between the two groups.  That's why you don't want to load to PF166 - need to get up to PF170 - 175.

 

 

[jwhittin]

OP - How were these two measurements taken? We're both results of the match chono? Did you check one yourself? If so how many rounds? 

[perttime]

How much temperature difference? That alone COULD explain it.

[jwhittin]

There is no way to know using the PF chrono results. 

 

Maybe the powder manufacturer knows the sensitivity or you could test your ammo at different temps.  Then load for worse case conditions.  

[open17]

Interesting.  WSF has a reputation of being REVERSE temperature sensitive----faster at lower temperatures.  My own experience

seems to bear that out, a 172 PF open load at 45° went 165.1 PF at Area 2 where the temperature was  85°.   

           

[Rwm983]

That can be the difference in Chonographs. None of them read the same. If you know anyone with a Labradar try it. They are the gold standard for accuracy.

[OrondoShooter]

Lot variation of powder, or temp even though it's noted as being opposite above, maybe Chrono differences too. Could be your powder implementation throwing off charges, I'd start there making sure you're getting 5.7 grsins every time. Of course, you should test some longer (10-20) strings of shots to see what your ED and SD are overall.

[jwhittin]

One huge problem is you can only load to 930 if your STD is below 6.5 fps.  Assuming a reasonable STD of about 15, you would need to load to 950 fps.  

 

What is your 8 round STD? Add at least twice that to velocity needed to meet PF for you bullet weight.  Problem solved!

Edited February 26, 2018 by jwhittin

[Hi-Power Jack]

I always run 20 rounds thru the chrono, and I want ALL of them to meet PF