low SD big group

BH30-06

Private
Minuteman
Aug 12, 2018
52
3
12
Canada
Hey guys,
I’ve just started loading for a 260rem, 1-8 twist barrel, new Lapua brass, H4350, cci br2 lg rifle, Berger 130 hybrids. The lowest SD I got was 4.0 using 40.4 grains of powder, with the bullet seated .020” off the lands, but the group I shot was 1.5” and I’m not sure why that happened. The best group I shot was with 42.0 grains of powder and it was 7/8”, the SD on that was 18. Should I stick with the smallest group or tinker with the one with the lowest SD. These were all shot at 100 yards.
 

Travclem

Dr. Dickweed
Belligerents
Jul 14, 2013
556
433
69
Lubbock, TX
How many shots are these SDs based on? Did you run an OCW? What do the groups look like? When asking load development questions, a picture is worth 1000 words.
 

frost1235

Sergeant of the Hide
Belligerents
Minuteman
Nov 3, 2018
139
32
34
Where it snows
I hate to be the one to say it, but it could be you. I always suggest doing load development on a sandbag instead of a bipod, with a stable rear bag that you aren't fighting in the prone or bench position.

Are you using a magnetospeed or labradar to find your SDs as well? That will affect group size vs SDs.

Normally, I'd advocate for the lower SD if the shooter has shown good groups in the past. At that point, it'd be am issue of seating depth.


But in your case, I am assuming you shot your groups with a magnetospeed on. Definitely take the magnetospeed off and use the lowest SD. If the groups are still big, adjust the seating depth as mentioned.

To add in, you're using virgin brass. Expect to tweak the load with fireformed brass. Unless the virgin brass was molded to the chamber or vice versa, You're going to see higher fps/velocities that will throw your node data off or see pressure signs if you're running it hot.
 

bodywerks

Gunny Sergeant
Belligerents
Jan 19, 2010
1,596
26
154
44
Tucson,Arizona
Bergers, even the Hybrids, can be finicky about seating depth. But all questions asked here need to be answered. Additionally, how are you, typically, as a shooter? Has this rifle already punched bugholes with other loads? Is it a custom rifle with an accuracy guarantee? So many questions/factors...