POI shift with new IMR 4064 batch

[SubMOAR]

Hello,

I have been using IMR 4064 for my .308 Win for a while now with great results. I always get great accuracy and low ES/SD's.

My go to load is the Hornady ELD-Match with 39.7 grains of IMR 4064, seated at 0.020" off lands. CCI 200 primers with LC brass. This load has been 1/2 MOA if I do my part.

I have a problem now though, I am running out of my Swiss made IMR 4064, and just received a new Canadian made batch. I loaded up several of each, and went out to compare at 100 yards to make sure the transition will be smooth. Unfortunately that is not the case. My Swiss IMR 4064 is zeroed with a velocity of 2,330 fps. I tried the Canadian made- IMR 4064 and found that the POI was over 4" low. Velocity was 2,305 fps.

With all factors being the same except the powder manufactured in different parts of the world, how can this cause such a drastic POI shift, especially since the velocity was not greatly different either? Accuracy of the Canadian made IMR 4064 was the same as the Swiss. This has to be something with barrel harmonics, I just don't understand it. Anyone have any insight?

 

[MASH]

A different lot of powder is just like buying a different lot of loaded ammo. It may be close but they are never going to be exactly the same. Some lots of powder are hotter then others. As long as your group sizes have stayed the same adjust your scope 4 inches and go have fun gun)

 

[philipbrousseau]

harmonics and possibly position on the bags.

 

[SubMOAR]

That's what I'm confused about, is how it would change the harmonics to release the bullet at a different location in the "whip", yet retain the same velocity. I have yet to do a true accuracy test to see if the Canadian made powder has the same accuracy. I only did one group and it appeared to be sub MOA, but I never actually measured it.

Bag placement has not changed, I use an Atlas Bipod with a commercial rear shooting bag. My Bell and Carlson stock makes it extremely easy to manipulate the rifle the same way every time.

Maybe this is a sign for me to switch to those new Enduron powders or Extreme powders? Like IMR 4166 or Varget? If Varget was not impossible to find in stock, I would have switched probably long ago.

 

[Sargesniper]

That's what I'm confused about, is how it would change the harmonics to release the bullet at a different location in the "whip", yet retain the same velocity. I have yet to do a true accuracy test to see if the Canadian made powder has the same accuracy. I only did one group and it appeared to be sub MOA, but I never actually measured it.

Bag placement has not changed, I use an Atlas Bipod with a commercial rear shooting bag. My Bell and Carlson stock makes it extremely easy to manipulate the rifle the same way every time.

Maybe this is a sign for me to switch to those new Enduron powders or Extreme powders? Like IMR 4166 or Varget? If Varget was not impossible to find in stock, I would have switched probably long ago.

If you are looking to make a powder change, VV-N550 is an excellent powder for .308 Win. I get excellent grouping out to 300 Yds. with it and 168 gr. SMK's.