Low SD but bad groups

[g8ters]

can you have really low sd (5) but have bad groups. Person behind the gun? I had a load work up for 6.5 PRC 156 eol and retumbo. Had three strings of 3 shots with eally low sds. But the groups were 2". I was shooting magpro earlier with 156 and had some good sd and 1/2 moa.

The retumbo sting was at the end of the shooting day. May be tiredness. But I don't think so. Just don't want to waste components to re-try.

These were 100 yards shots.

 

[Reelamin]

Was this load development or established load, What were groups like with wide SD, other bullets, other powders, other OAL's, other primers etc. etc. ?

 

[DUCKMAN11]

Velocities of the good groups vs bad groups?

2" round groups or more vertical or horizontal?

I think you are in a bad node for that barrel or you got something loose on the rifle. But thats a guess at this point.

 

[Mikecr]

You can have a powder node that puts you way away from a barrel node.
They're different things

 

[MagnumManiac]

Small ES & SD do not make it a given for good groups.
I have a short course (100mtr) load that has an ES of 100….it prints into the .1's.

Cheers.

 

[Hugnot]

Bad vibes

 

[Dmagna]

can you have really low sd (5) but have bad groups. Person behind the gun? I had a load work up for 6.5 PRC 156 eol and retumbo. Had three strings of 3 shots with eally low sds. But the groups were 2". I was shooting magpro earlier with 156 and had some good sd and 1/2 moa.

The retumbo sting was at the end of the shooting day. May be tiredness. But I don't think so. Just don't want to waste components to re-try.

These were 100 yards shots.

Change the seating depth

 

[g8ters]

Thanks all for the info. It was the end of the session. Barrel hot but I cool 5 min between each string. Carbon barrel. So it's not a whippy light barrel. Not vertical stringing. Just all over the place. I thought it was me. But 2" is not typical me for 3 straight groups. Just trying to get retumbo and magpro as a back up powders then the n565 runs out. Retumbo was very good at lower velocity (very good sd and maybe a node) but when I went higher even though the low sd, the group really opened up.

I'll keep the data. May revisit, but I just don't want to waste components right now if I don't have to. I may have to live with lower velocity node when I use the powder.

 

[nhhunter]

Seating depth. You'll find a happy place

 

[DUCKMAN11]

Change seating depth or try a barrel tuner. I'd get an EC tuner before I messed with seating depth because it's not going to change your ES/SD, it's just going to change your barrel harmonics. And not eat up components. I can usually get an EC tuner "set" in 10 rounds or less. This is all assuming that you are not shooting suppressed.

 

[Flintlock shooter]

Another vote for playing with seating depth. If that doesn't work, try going a 10th or two either way with powder charge.

 

[BrentM]

Some fps nodes are very narrow and can produce low sd but barrel time node is not good. I'd post the fps and barrel length and then take advice and find a seating depth the barrel likes. I run 2.950 coal and a 2915 in a 22". Same load in a 18" runs 2820 ish. Both shoot very well.

 

[Orange Dust]

My $.02. If you can't get it to group with seating depth try a different primer, then powder. But if it was me and the depth didn't tighten it up I wouldn't mess with it. I'd start over with a different bullet. don't have the patience any more.

 

[birddog 68]

If you had low sd and.5 moa with magpro why switch to retumbo? Nothing wrong with trying different powder but sounds like you were on the right path and decided to veer off