Load Help

[Brux]

Shot my new rifle yesterday for the first time.It shot great.My loads were.308 cal
42GR varget,168 match Fed 210 primers
42.5 GR varget and same above
42 GR RE15 same as above
42.5 GR RE 15 same as above
42 GR IMR 4064 same as above
42.5 GR IMR 4064 same as above
Hornady Brass
All 3 loads with 42 GR's of powder shot .29 to .35 groups
Went back with the same loads today and they opened up to 1/2 inch groups or maybe a little more.
Same bullets,brass,powder,primers,the only difference was the brass was now fire formed to my chamber,yesterday it was new,so when I resized I only bumped the shoulders back a 1 thou.What could have caused this?Shot 50 rounds yesterday.Could it have been the barrel broke in as I was finishing up yesterday?The reason I ask this is because the last rounds fired yesterday were the 4064 loads and they shot almost identical with a .5 GR of powder difference.Whats your thoughts?

 

[Grumulkin]

1. It could have caused by such things as different ambient temperature, different shooter performance, etc.

2. It's a myth that fireformed brass always shoots better than new brass or that fire formed neck sized brass always shoots better than full length sized brass. You may need to fiddle with your sizing technique.

 

[mtrmn]

Size some back to new spec and see if your groups shrink again......

 

[Brux]

Yea,I always fireform my brass and then size it to the chamber.That's all I did different.The groups still clover leafed but were bigger.

 

[Brux]

Anymore ideas on this?Do you think I should try changing charge weight.