OCW for 338LM with Berger 250 Hybrids

[gasdoc09]

OCW workup today. I've shot the 250 gr Berger hybrids before after a quick load workup, and thought I'd revisit them today.

This was out of a 338 Lapua Magnum TRG-42 with 1x12" twist.


New Lapua brass, Redding neck sizer only with a 365 bushing. Fed large rifle magnum match primers. Retumbo powder.

Berger's web site lists 86.5 as minimum charge and 94.0 as maximum for Retumbo, so per the instructions on Dan Newberry's web page I settled on 86.5, 88.2, and 89.9 gr for the first three rounds, then 3 each of 91.8, 92.4, 93.1, 93.7, and 94.4

Went to the range and shot the first 3, then the remaining 15 round-robin, from a rest through a chrono to a 100 yard target.

Load data:

Case Info        Bullet             OAL     Primer   Powder         V1    V2    V3     Avg      SD    ES
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 86.5  2503              2,503.0           0
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 88.2  2584              2,584.0           0
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 89.9  2671              2,671.0           0
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 91.8  2763  2754  2773  2,763.3   9.5    19
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 92.4  2785  2790  2786  2,787.0   2.6     5
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 93.1  2819  2810  2812  2,813.7   4.7     9
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 93.7  2843  2836  2848  2,842.3   6.0    12
0x Lapua 2.720”  250 Berger hybrid  3.681”  Fed215M  Retumbo 94.4  2862  2861  2854  2,859.0   4.4     8

OCW math:

             --shot1--     --shot2--     --shot3--
             x1     y1     x2     y2     x3     y3      x-avg  y-avg    Grp Size
91.8 gr     0.26   0.09  -0.92  -0.51  -1.26  -0.50     -0.64  -0.30    1.64"
92.4        0.00   0.00   0.15  -0.50  -0.99   0.18     -0.28  -0.10    1.31"
93.1        0.04  -0.17   0.51  -0.66   1.50   0.01      0.68  -0.27    1.46"
93.7        0.52   0.23   0.41  -0.11   0.73  -0.42      0.55  -0.10    0.67"
94.4       -0.34  -0.15  -0.18   0.21   0.82   0.56      0.10   0.20    1.36"

OCW graph showing average point of impact relative to aim point:

I know group size is not the point of an OCW workup, but I was still really disappointed with the >>1 MOA groups (except the 93.7 gr group). I didn't feel like I had any fliers. Low wind. After this, I shot 5 rounds of 250 gr Lapua Scenars into a .64" group.

What do you experts make of this? What's next? Thanks.

 

[Dan Newberry]

Your graduations (though I do agree are on the 1 percent scale) are a little large, and therefore the tightness of the groups isn't what it could be.

Your decent group at 93.7 may indicate that there's a good node in that area... revisit that area with .3 grain charge variations and see how things look.