Different powders, different groups

[Lennyjoe]

Wow is all I have to say.

I have a pretty good load worked up already for my 22-250 using Varget and 50gr V-Max bullets so I figured I'd try out some different powder and see what happened. The V-max load is giving me just under .75" @ 100yds.

So I try H-380 to which is suppose to be the cat's meow for 22-250 and what a difference. I couldn't get a good group out of the powder and it was hitting 7" left of where I had the V-max load zero'd at. I had several loads worked up from 39gr to 41gr and standard C.O.L. to which none would group less than 2" @100yds.

Needless to say I am not too impressed with the H-380 and plan on going back to the Varget. Maybe I'll give some other powders a try.

 

[~z]

Funny you should mention it, over the weekend I worked up a load for a guy with 380. 22-250 box stock Savage (pre acutrigger) with about a 9# pull. I figured this thing would not do better than 1" @ 100 no matter what I did. he said it wouldnt shoot better than 3" @ 100 with 5 or 6 different factory rounds. I loaded up a ladder at different seat depths with some ballistic tip boat tailed 55gners and the ole 38.0 gn of H380. Figured up the ones that shot the best and then adjusted powder weights. Working with 4 shot groups (three to tell the tale and one for me to whiff) I soon found accuracy. To my amazement, the gun printed 2 groups (three shot)under .1500". 39.2 and 39.4 gn. I loaded him up 50 at 39.3 gn of 380.

 

[brickeyee]

Any change in powder (even a different lot of the same type) is more likely than not to change accuracy.
Minor changes in barrel vibration and dwell time can spread things out pretty badly. Even the same velocity from a different powder does not guarantee that the vibration pattern is the same. The peak pressure may be at a slightly different point in bullet travel affecting vibration.

 

[bogie]

What do you expect?

Try some different seating depths while you're at it.

 

[Lennyjoe]

What do you expect

A bit of variance but not 7" difference.

 

[cracked butt]

I use a kind of nonconventional method for testing a different powder. I'll graph powder charge weight vs velocity as published in a reloading manual for a powder that I have a good acurate load for. I'll graph the powder that I want to test on the same chart. Next I take the point on the line representing the velocity of the accurate load of the first powder and draw it to the same velocity point of the other powder to give me a rough idea where to start.

In the case below, using the 170 gr bullet and 50.0 gr of IMR 4064, I was able to determine a ballpart figure of where to start with imr 3031. The estimated charge where the IMR 3031 would perform the best in this rifle was only 1/2 gr off. It doesn't always work, but much of the time its pretty close.