Thread: Optimal Charge Weight / OCW

Tried OCW test this morning for 150gr Speer SPBT in the 788, progression was sighters (-7%, +2, +2) loads (+2, +0.7, +0.7, +0.7)

Can someone pls try to explain why the focus for OCW is more on POI than group size ? Not sure I get it...

For 2208 the start load is 44.0 and max is 47.0

Measured the groups by zeroing vernier on 308 head, and then measured side to side.

46.3gr: group 1.332, poi 1.356 (low left)
46.6gr: group 0.752, poi 1.716 (low left)
46.9gr: group 0.758, poi 0.807 (low left)
47.2gr: group 0.273, poi 0.808 (low left)

Getting flattish primers, but no cratering or ejector marks on all these loads (210 Fed primers). Bolt lift is heavy on all of them, but that is apparently a known issue on 788 (short handle and steep cocking cam)

Next I'll try some lighter progression - sighters (-10%, +2, +2) loads (+2, +1, +1, +1) so that will give me 44.9, 45.3, 45.8 and 46.3

Im not up on the prescribed formular for a ocw test but thought it was basicly a ladder looking for where a few different charges landed very close or closer than the rest to each other.
Hence in the middle of that would be "optimum charge weight" as a slight variance in charge,temp,neck tension,fouling will have the minimum effect on point of impact from zero.
But i have been wrong once or twice before.
Looks like yours wants to run fast :thumbup:

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VC, just found some references to flat primers with non max loads being headspace indicator. The rifle does have bit of headspace issue, going to load some fire formed cases tonight and check what happens to their primers.

SSR cut it to 18, and did real nice job on the crown

If I can get close to that last group, will be a very happy camper... Not too shabby for a 40 year old rifle

K, emailed Dan Newberry and got this reply:

If you choose a powder charge that allows for a point of impact shift with only a slight pressure change (like .3 grains of powder would induce), then when a pressure change comes from an odd brass case, or temperature change in the air, or such, you'll get a flyer. The most consistent load recipe is one that is going to tolerate some pressure change and still shoot to point of aim.

I've loaded a string with .5 gr increment into fireformed brass to check the pressure thing. All primers now nice and round, bolt lift did get heavy from 46.0 up, so all good