OCW quick test today...pls comment on results

cali_tz

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Tried to do a quick OCW test this afternoon at 100 yards, with my 338LM. I had to go zero in a new scope and mount (Spuhr 34mm... very nice kit).

The results are in the following image. It's all marked, but bullet is 250gn Scenar, powder is VV N570, Fed 215M, Hornady brass, 50deg F, Steyr 338LM rifle with 27" barrel, wind right to left 3-6mph. The 97.0 gn load seemed pretty tight, but the 98.3 gn load had also very low vertical stringing.

On one hand I'd love the 3000+fps velocity that the 98.3 gn would give me, but perhaps the 97.0 would be easier on brass/primer pocket and be more accurate at 1000+ yards where I want to play. But at 1500-2000 the 97.0 gn might fall a bit short since it's MV is probably closer to 2900??? I didn't chron today so I have no speeds to go along with these target pictures.

Your feedback appreciated.



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Hedge

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Re: OCW quick test today...pls comment on results

From the test it looks to me that your node is around 97.3. However, if you're willing to drop the velocity a bit, I'd test a few tenths under 97 gr to see if 97 is your OCW.
 

MALLARD

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Re: OCW quick test today...pls comment on results

the n500 series is temp senstive , i dont think 1 grain matters in terms of brass life or velocity, maybe 20 fps.

but a case with nearly 100 grains full of temp sensitive powder , you could see allot of variation in nodes and velocities because of that, so , things can change
 

cali_tz

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Re: OCW quick test today...pls comment on results

I googled around a bit and saw some benchrest discussion that seemed to indicate N560 was not particularly temp sensitive according to their winter and summer loading experience. Plus you'd think the Finns would make temperature tolerance a part of their engineering spec for powder, given their extreme temp swings there.
 

MD2Colo

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Re: OCW quick test today...pls comment on results

I'm a cherry at this OCW thing, but don't you wanna move it back a bit to like 200 or 300? Especially with that 338 cannon you're firing?? But I guess if that's all you've got, you gotta make do. I would be curious to see the test at 3 or 400. No 300 grain bullets?
 

cali_tz

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Re: OCW quick test today...pls comment on results

Yes MD2, I agree. However my local range is only 100 yards max.
Yes I have 300 Scenar and will do that test as well, and run both 250 and 300 at a 200 yard range hopefully.
 

MD2Colo

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Re: OCW quick test today...pls comment on results

COol man. That 338 is a monster...98 grains of powder... jesus H...

Have a good one.
 

cali_tz

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Re: OCW quick test today...pls comment on results

today's results... quite interesting, learned something new. WIth N570 powder, there was NO difference in speed between 98.3 and 98.8 (Lapua's max load) ... exactly same. See the groups in the attached pic... I tried 98.8, 97.0 (again) and 98.3. As Dan predicted over at his OCW site, the 98.8 and 97.0 are nodes.

There is one flyer as I moved the rifle slightly on trigger pull on the 97.0, otherwise that was four shots in the one group. On the 98.8 that was a total of 7 shots in the one group. I didn't think this rifle could do that tight. Also this was shooting on a concrete bench, and I think I could do a smidge better on my mat shooting prone.

This was N570 powder, 250gn Scenar, and at 103 yards. There was a healthy 4-8mph right to left wind. 53F temps. DA about 2700 feet.
Red circle is POA. The target is one inch boxes with a lighter line at the half inch mark.

I'd encourage others to try developing their OCW sweet spot. It does seem to work.



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okiefired

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Re: OCW quick test today...pls comment on results

In your second post your increment spread is too wide to tell anything. Remember in the OCW method, you're not really concerned about group size at first, you're looking for same point of impact for several qroups consecutivly. In your first post, 97.0-97.7 were all same POI. At 98.0, the POI began to move up. If it were me, 97.3 is what I'd be playin with IF velocity is where you want it.

okie
 

cali_tz

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Re: OCW quick test today...pls comment on results

I better go back and re-read the OCW method once more.
 

okiefired

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Re: OCW quick test today...pls comment on results

Yeah, when you come up with several loads in a row that are same POI, take the middle one and start playing with things like bullet seating depth or maybe changing the charge .1gr one way or another to tighten things up. That 97.3 was a pretty damn good grp to start with. Little variances are the difference at short ranges like 100 and are sometimes hard to read, especially with something like a big .338. Good luck.

okie
 

cali_tz

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Re: OCW quick test today...pls comment on results

Okie, thanks for the feedback... I went back and reread the OCW procedure and understand what you are saying. I have more to do here on this load development. Thanks.