Good SDs but horrible accuracy?

[Corse]

I have been trying to get some Nosler 70gr RDFs to shoot and I tried some 748 today with both the RDF and 69 TMK.
The RDF had some decent SDs (8.8) but absolutely horrible groups, I didn’t measure, but 5” would be generous. The TMK had a SD of 1 for two separate charge weights and the third was 0, but similar groups to the RDF.
I shot a control group with 52gr MK and it was typical of the gun @ 0.4”.

Has anyone experienced anything like this before?

[gaijin]

What were they shot from, barrel twist?

[Corse]

It was a stainless 18” proof research 1\8 twist.

[gaijin]

Assume no sign of yawing/destabilizing? The 1/8 should be just fine with heavier bullets you listed.

And no, I’ve never experienced that.

[Corse]

They were stabilized. I’ve never had SDs that good, but I have also never seen accuracy that bad.

[Nightvisionary]

Low Standard Deviation as a general rule is a good measure and goal but it is not the end all in reloading accurate ammunition. Over the years I have had mediocre accuracy from low SD loads and excellent accuracy with SD's in the 20's. There are enough variables in the process that a single factor may or may not contribute to overall consistency.

[gaijin]

Sure.
Accuracy, at least reasonably "close range" accuracy, is certainly NOT unusual with fairly high SDs.

THIS is the unusual part of your issue Corse; "I shot a control group with 52gr MK and it was typical of the gun @ 0.4”."
Better than average accuracy with the 52's doesn't add up to shotgun patterns with the heavier 69 TMKs and a 1/8 twist IME.

[markm]

THIS is the unusual part of your issue Corse; "I shot a control group with 52gr MK and it was typical of the gun @ 0.4”."
Better than average accuracy with the 52's doesn't add up to shotgun patterns with the heavier 69 TMKs and a 1/8 twist IME.

Absolutley. I wanted to chime in with some sore of suggestion, but I'm stumped. It's VERY hard to make a SMK shoot bad.

[Corse]

Agreed, the SMK have always shot decently at worst, the RDF has been alright at best.

I’m not sure what else I should check or if it is even worth pursuing 748 with the RDF. The lowest charge weight I tried was somewhat better, but at that point the velocity maybe too low for that weight of bullet (<2800) to make it worthwhile.

My best results with XBR were around 2790fps with 3/4” groups. Too bad I have 700 of these left.

[Bimmer]

The TMK had a SD of 1 for two separate charge weights and the third was 0...

Really, SDs of 0-1? I'm impressed... almost incredulous.

Throwing stuff at the wall: Given that the rifle and the bullets aren't the issue, maybe your charge weight is too high/low? Or your seating depth is off?