OCW test: Help me interpreting results
- Thread starter jnesto
- Start date
I’d like to hear your reasoning as to why you think that 40.4 is part of a node that also includes 40.0 and 40.2. And assuming that your reasoning were sound regarding 41.0-41.4 being a node, why would you choose 41.4 as your OCW?
I’ve asked these questions as an educational endeavor.
I’ve asked these questions as an educational endeavor.
D
Deleted member 113831
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It would be much easier to judge if the aiming dots were all on a straight line. The idea is to compare group position not only to POA, but to one another.
@ditter Unfortunately chrono was not available.
Rifle: Rem 700 5R 20” .308
Load: Federal Brass, Magtech LR primer, 175 SMK. COAL: 2.800"
@lash base on my understanding, from Mr. Newberry's instructions, ploted shots that come the closest to hitting the same POI (point of impact) on the targets.
@Skookum Good catch! Next time I will use the official OCW target.
Rifle: Rem 700 5R 20” .308
Load: Federal Brass, Magtech LR primer, 175 SMK. COAL: 2.800"
@lash base on my understanding, from Mr. Newberry's instructions, ploted shots that come the closest to hitting the same POI (point of impact) on the targets.
@Skookum Good catch! Next time I will use the official OCW target.
Since you read Dan Newberry’s instructions, I suggest you follow the formula he provides to determine charge weights as well. Typically at charge weights around 40 grains +/-, the increments are 0.3 grains. Doing 0.2 grain increments can make finding the node a little more difficult.
This said, based on the target above, 41.2 would be the node based on the group centers relative to POA
This said, based on the target above, 41.2 would be the node based on the group centers relative to POA
As Skookum so correctly pointed out, it would be much easier to read if the dots were all on the same line to start with. Having said that, 40.4 poi is nowhere near the same relationship as 40.0 and 40.2. If you look at the rise and run (x and y coordinates) of the center of each of those groups carefully, you will see that.
As to choosing 41.4, I asked because 41.4 is the third and last point in a group of similar poi. You choose ocw based on the most forgiving charge weight in a node. In this case that would be 41.2, the middle charge in that node. This allows for some of the natural variations you will experience, such as charge variations, temperature swings and minor pressure differentials caused by other variability introduced by your loading practices and your environment.
Just as a point to consider, don’t hesitate to go back and read all the points of Dan Newberrys OCW instructions more than once until you really get to understanding not only what, but why. It will help you a whole lot.
As to choosing 41.4, I asked because 41.4 is the third and last point in a group of similar poi. You choose ocw based on the most forgiving charge weight in a node. In this case that would be 41.2, the middle charge in that node. This allows for some of the natural variations you will experience, such as charge variations, temperature swings and minor pressure differentials caused by other variability introduced by your loading practices and your environment.
Just as a point to consider, don’t hesitate to go back and read all the points of Dan Newberrys OCW instructions more than once until you really get to understanding not only what, but why. It will help you a whole lot.
D
Deleted member 113831
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What powder?
41.0-41.4 are pretty stable.
41.6 has that one shot going high, but you will notice that it goes to the exact place that the following 41.8 charge goes to. So 41.6 is likely on the very edge of the node.
As @lash has already mentioned, I would load 41.2 if it were me.
Side note: Notice your group shapes. They follow a pattern.
40 = round/horizontal
40.2 = vertical
40.4 = vertical
40.8 = round/horizontal
41 = bughole
41.2 = round/ horizontal
41.4 = vertical
41.6 = vertical *(edge of node, could have been bug hole if hadn't scattered)
41.8 = bughole
41.2 being next to a bughole means it should only take a slight change in seating depth (.005" at a time) to get it to tighten up considerably.
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@Sig Marine you are right, it seems some people (including myself) are either unfamiliar with the OCW test or how to do it properly.
Going back to Mr. Danberry's explanation we can see YOU MUST load up THREE rounds at your starting charge weight and increase the charge weight in 0.3 grain increments, load up 3 more, increase by 0.3 again, load up 3 more, and continue doing this until you've reached book max for your powder and projectile. Will try again this test using 0.3 powder charge increments. Now it is clear why 0.3 increments and not less than that. The idea is to add a gradual increase in powder that isn't so fine that it'll take forever to get through the OCW, and not so large a jump in powder charge that you skip half the node because you jumped up 0.6 grains at a time.
@lash and @Skookum thanks for your feedback. When life gives you lemons, make lemonade!
Will try to do my lemonade with this test and for the next one I will be more precise following the input you guys posted here.
Going back to Mr. Danberry's explanation we can see YOU MUST load up THREE rounds at your starting charge weight and increase the charge weight in 0.3 grain increments, load up 3 more, increase by 0.3 again, load up 3 more, and continue doing this until you've reached book max for your powder and projectile. Will try again this test using 0.3 powder charge increments. Now it is clear why 0.3 increments and not less than that. The idea is to add a gradual increase in powder that isn't so fine that it'll take forever to get through the OCW, and not so large a jump in powder charge that you skip half the node because you jumped up 0.6 grains at a time.
@lash and @Skookum thanks for your feedback. When life gives you lemons, make lemonade!
Will try to do my lemonade with this test and for the next one I will be more precise following the input you guys posted here.
The increments at which the test weights for the OCW is shot will change depending on the amount of powder used. I know from doing many in the 35-45 grain max charge weights that the increment is 0.3 grains. If and when you start shooting larger calibers that use more powder and have a higher maximum charge weight, that the increment will increase between OCW charge weights.
The OCW process and performing the test is not difficult; Dan Newberry explains it well and gives examples but too many shooters try to find the results they're looking for rather than understand the results they get
D
Deleted member 113831
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This will be a bit controversial, but after doing these tests over and over through the years and looking at many, many others as well, I've shortcutted my own process by quite a bit.
I have noticed that the most forgiving and tunable loads (notice I didn't say the utmost accurate loads) tend to show up about 2% off of where max pressure is found.
For my needs, I want a load to depend on day after day regardless of conditions.
What I do is find max load by loading 2 rounds per charge in 1% increments. I make careful note of all observable signs to determine when I've reached max. These include: velocity, appearance of powder on neck, position of powder ring on neck, amount of expansion measured at the pressure ring at the base, appearance of ejector marks...all of these taken in consideration together will tell you where max is.
I then back off 2% and bracket that point by loading 5 at (2%- 0.2grains), (2%), (2%+0.2grains), (2%+0.4grains).
I don't care about any slower, I need a respectable speed...I don't wanna go higher and risk running into high pressure in summer heat. The "middle node" will very likely show up in this area.
I shoot these at 200 yards and look for the same patterns of POI and group shapes mentioned above. I then move to seating depth tuning.
I haven't had a test done this way fail to produce a clear result yet.
Not saying this is the best way or only way. This is just my personal shortcut that has thus far gotten me to the same eventual place a bit quicker.
I have noticed that the most forgiving and tunable loads (notice I didn't say the utmost accurate loads) tend to show up about 2% off of where max pressure is found.
For my needs, I want a load to depend on day after day regardless of conditions.
What I do is find max load by loading 2 rounds per charge in 1% increments. I make careful note of all observable signs to determine when I've reached max. These include: velocity, appearance of powder on neck, position of powder ring on neck, amount of expansion measured at the pressure ring at the base, appearance of ejector marks...all of these taken in consideration together will tell you where max is.
I then back off 2% and bracket that point by loading 5 at (2%- 0.2grains), (2%), (2%+0.2grains), (2%+0.4grains).
I don't care about any slower, I need a respectable speed...I don't wanna go higher and risk running into high pressure in summer heat. The "middle node" will very likely show up in this area.
I shoot these at 200 yards and look for the same patterns of POI and group shapes mentioned above. I then move to seating depth tuning.
I haven't had a test done this way fail to produce a clear result yet.
Not saying this is the best way or only way. This is just my personal shortcut that has thus far gotten me to the same eventual place a bit quicker.
