OCW method-help

tactical_tech

tactical_tech

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I just finished my first Optimum Charge Weight trial. Would like your guys opinion on picking some powder charges that would warrant further testing. All of them are 5 shot groups. Shots fired at 100yds with about a minute or two between each shot.

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I understand OCW to be a search for a charge weight that has room plus or minus where impact on target is not going to change very much, so .2 or .3 grains plus or minus isn't going to affect trajectory. Probably art as much as science. If that were mine, I'd re-shoot 43.5 through 45.0 - elevation looks pretty consistent, but would want to confirm about apparent drift to right at higher end of that series. Not sure what you are shooting or what you hope to accomplish. Amax bullet would be for target / steel / silhouette, not usually for hunting?? Would think you already are good to go for silhouette??
 
I would say go 0.2 gr from 44 -45gr. I would bet 44.3 - 44.5 you will hit the spot. There is not much vertical there, thats what you want....Most 308's, using the same powder, and same bullet, will have a node there. To me, 46 is a nice group, and maybe worth exploring more, but your case is prob already full.... also, at 46, the POI is different than the rest, and it is more vertical - which is what the OCW theory says to shy away from.
 
Potashminer said:
I understand OCW to be a search for a charge weight that has room plus or minus where impact on target is not going to change very much, so .2 or .3 grains plus or minus isn't going to affect trajectory. Probably art as much as science. If that were mine, I'd re-shoot 43.5 through 45.0 - elevation looks pretty consistent, but would want to confirm about apparent drift to right at higher end of that series. Not sure what you are shooting or what you hope to accomplish. Amax bullet would be for target / steel / silhouette, not usually for hunting?? Would think you already are good to go for silhouette??
Click to expand...

This is just for target shooting, no hunting. I did notice the slight drift as well, there was a little bit of wind today. May be the cause, not sure.

I usually would just pick the tightest group. The OCW method like you said seems to be about consistency, I honestly thought I would see a bit more variation than what I did. It seems like 43.5-45.5 all seem to be pretty consistent as far as vertical dispersion goes.
 
With due respect, the OCW is about finding the most consistent horizontal and vertical dispersion among a series of loads, not necessarily the one "best" load. Similar to the "ladder testing" that some reloaders use. The idea is to find a range of powder loads where you could be "sloppy", perhaps by dispensing powder from a scoop, (and therefore having varying charge weights), and still get decent groups. (and yes, I do know that certain famous folk have demonstrated they can dispense exceptionally accurate loads with a scoop! :) The opposite of OCW would be a very nice grouping load, but if you varied the charge + or - .1 grain, the bullets would go somewhere else.
To the OP - you did not mention, but as per the OCW procedure, did you fire these shots "round robin" to make up the groups, or did you shoot one entire group at a time?
 
Potashminer said:
With due respect, the OCW is about finding the most consistent horizontal and vertical dispersion among a series of loads, not necessarily the one "best" load. Similar to the "ladder testing" that some reloaders use. The idea is to find a range of powder loads where you could be "sloppy", perhaps by dispensing powder from a scoop, (and therefore having varying charge weights), and still get decent groups. (and yes, I do know that certain famous folk have demonstrated they can dispense exceptionally accurate loads with a scoop! :) The opposite of OCW would be a very nice grouping load, but if you varied the charge + or - .1 grain, the bullets would go somewhere else.
To the OP - you did not mention, but as per the OCW procedure, did you fire these shots "round robin" to make up the groups, or did you shoot one entire group at a time?
Click to expand...

I shouldn't have said "group". What I meant was more of a node. Shots were fired round robin, one shot per each charge weight starting from lowest to highest, then highest to lowest till each charge had a 5 shot group.
 
Myself I would try 43.5-44, then play around with seating depth.

Ive been only reloading a couple years now, so my knowledge might be a little green. :)
 
In my opinion, you stopped one load too soon. I'd bet dollars to donuts that 46.5 would have printed in the same ballpark as 46.0.

Dan Newberry says that you should plot the center point of your groups and go from there. The center point of 45.5 and 46.0 is very close (about half inch up and half inch right of center).

Guess what? The standard accuracy node for a 168-grain bullet with Varget is in the range of 45.5 to 46. This tends to be so common that when I start loading a 168 in a new rifle, I tend to start around 44.5 and work up to 46.5. In almost all cases, I've found 45.5 to be the winner, but anywhere between 45 and 46 is normally considered the sweet spot (at the top end).
 
Potashminer said:
With due respect, the OCW is about finding the most consistent horizontal and vertical dispersion among a series of loads, not necessarily the one "best" load. Similar to the "ladder testing" that some reloaders use. The idea is to find a range of powder loads where you could be "sloppy", perhaps by dispensing powder from a scoop, (and therefore having varying charge weights), and still get decent groups. (and yes, I do know that certain famous folk have demonstrated they can dispense exceptionally accurate loads with a scoop! :) The opposite of OCW would be a very nice grouping load, but if you varied the charge + or - .1 grain, the bullets would go somewhere else.
To the OP - you did not mention, but as per the OCW procedure, did you fire these shots "round robin" to make up the groups, or did you shoot one entire group at a time?
Click to expand...


Potashminer (and everyone else),

What is the prescribed way for doing this? I've typically shot 5 shot groups of the same charge before moving on to the next one; it never occurred to me to fire these round robin as the OP did. In a way, it makes sense to me though.

The other thing I've always wondered is that after so many rounds with a couple minute break in between each, how certain can one be other factors such as barrel heat, potential copper-fouling, etc. are not affecting the ultimate outcome of these results? Over the course of time it takes to fire that many shots, where I shoot anyway, the wind always invariably shifts or changes during the day as well.

I have been experimenting with the same bullet and powder as the OP but have yet to test as many loads over such a wide range as consistently and methodically as he has. I've found 42.5 Varget to give me 0.3-0.7 MOA fairly consistently (which was my starting point) so was hesitant to mess with it. In reading this thread now, I think I have reason to revisit that thought...
 
OP Don't mean this as a shot but I would really suggest reading Dan's article 3-4 times and really reading it. There are a lot of steps if you're doing it manually like you are it is about selecting the POI that is the CLOSEST together. Not the tightest group and once you decide on a charge you then have to adjust your jump to tighten up your group in your next series of test. However HeavyThread's program (HT great program writing BTW) seem to have done the work for you to provide you a starting point for a charge weight. On Target Calculator would be a commercially available program for to analyze your POI as well for OCW studies.
 
308BAR said:
OP Don't mean this as a shot but I would really suggest reading Dan's article 3-4 times and really reading it. There are a lot of steps if you're doing it manually like you are it is about selecting the POI that is the CLOSEST together. Not the tightest group and once you decide on a charge you then have to adjust your jump to tighten up your group in your next series of test. However HeavyThread's program (HT great program writing BTW) seem to have done the work for you to provide you a starting point for a charge weight. On Target Calculator would be a commercially available program for to analyze your POI as well for OCW studies.
Click to expand...

No worries, I corrected myself in an earlier post. I meant more of a node then a group. I've read Dans process a few times. Im aware the OCW method is not meant to find the tightest group but more or less the most consistent charge range that will have the least impact on point of impact. I was mainly asking for help on picking some charge ranges that would be worth while pursuing further testing. This is my first crack at the OCW method and was honestly expecting to see a little bit more of a POI impact change than I did, hence asking for help.
 
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