OCW and SD??

Moorvogi · Mar 13, 2019

Truth be told, i'm new to OCW still. BUT... is my assumption too far off that an OCW would have a good/decent standard deviation?

I did an OCW set for 22-250 using 4064 powder. Ended up with 3 sub moa groups that were also very similar POI. I picked the middle of the 3 charge sets and loaded 10 rounds. Shot those thru a chronograph and got a SD of 61?!

That seems high to me for an OCW... compared to my 300 win mag OCW load (4350) my SD is only 12 if i recall correctly.

I guess there's really two questions i'm looking for answers/info on.

1.a is 61 what you would consider an acceptable SD, assuming its also an OCW?
1.b if not what do you consider a good "range" of tolerable SD?

Moorvogi · Mar 13, 2019

I did some poking aorund and found a good site that "has an app for that". I didn't buy the app but it shows the predictions based on SD variance. Granted, the target is 1000yards not the 300-500 i'll be making but... i'm going to do this with a different powder something. Because.. load testing is a fun kind of frustrating.

https://precisionrifleblog.com/2015/04/18/how-much-does-sd-matter/

Moorvogi · Mar 13, 2019

This.. was the "meme" i was looking for.. because memes are all the hype... or something.

how-much-does-muzzle-velocity-standard-deviation-sd-matter21.png

Uncle Duke · Mar 13, 2019

Standard deviation of 61 over 10 rounds is what I think you're saying? 20 rounds would be more telling, but even with a sample size of 10 rounds, I'd be thinking that indications are that something is likely amiss.

I personally love 4064 in .22-250. Initial thought would be that I am inclined to doubt you have a powder related problem.

I assume you're weighing your charges? If so, my next question would be what you're using for brass?

Moorvogi · Mar 13, 2019

yes. i do start w/ a throw then trickle in the rest to the intended charge. now that i think about it... i wonder if the scale isn't acting up or flakey. it's a digital scale and sometimes it needs to be rezeroed becuase it'll show 0.8 gr when theres nothing in the pan. i wipe everything off.. stil there.. i re-zero the scale and its good. something else for me to look into.

the brass, is once fired hornady brass. it was a new rifle so i bought NEW ammo to zero the scope etc etc the reloaded it w/ handloads. so it's a true "once fired" not "once by someone and 90 by someone else hahaha".

the bullet was seated to a depth indicated in the nosler book and i'm shooting nosler ballistic tip: varmint projectiles and no crimp.

back to the scale for a moment.. sometimes the scale goes from 34.5 down to 34.4.. or up to 34.6. i puts with the powder for a minute to try to get it 34.5 exactly but.. it makes me wonder.. could that +/- 0.1gr .. be the 60fps??

Pinecone · Mar 13, 2019

SD numbers are fine, but the load shoots, the load shoots.

Uncle Duke · Mar 13, 2019

Moorvogi said:
yes. i do start w/ a throw then trickle in the rest to the intended charge. now that i think about it... i wonder if the scale isn't acting up or flakey. it's a digital scale and sometimes it needs to be rezeroed becuase it'll show 0.8 gr when theres nothing in the pan. i wipe everything off.. stil there.. i re-zero the scale and its good. something else for me to look into.

the brass, is once fired hornady brass. it was a new rifle so i bought NEW ammo to zero the scope etc etc the reloaded it w/ handloads. so it's a true "once fired" not "once by someone and 90 by someone else hahaha".

the bullet was seated to a depth indicated in the nosler book and i'm shooting nosler ballistic tip: varmint projectiles and no crimp.

back to the scale for a moment.. sometimes the scale goes from 34.5 down to 34.4.. or up to 34.6. i puts with the powder for a minute to try to get it 34.5 exactly but.. it makes me wonder.. could that +/- 0.1gr .. be the 60fps??

No way of knowing about your scale, but no I don't think .1 grain would cause your swing. More than that would make sense, if that's possibly happening. More likely to cause that swing I think would be a significant variation in the capacity of 1 or more of your cases. That's definitely not unheard of, even with the same brand of brass. It's one of the primary reasons that make expensive brass expensive, not that I'm advocating you need go that route. But with a SD of 61, you're looking at a swing of 122 fps between high and low reading off your average. That's a bit much, even with a small sample size.

Not sure what you're encountering, but it's also not impossible that your chrono can be the culprit sometimes, so worth keeping in mind also.

Moorvogi · Mar 13, 2019

hrm... maybe what i'll do is.. kick a target out to 200 and 300y.. see what the group size is for several sets of 4 shot groups at the same range. i mean.. really i dont care that much about the SD.. as long as it's hitting the mark where i think it should be at the intended ranges. (out to 600y)

OCW and SD??

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