New to OCW - please help interpret what I'm supposed to be looking for

[ReaperDriver]

HI all,

I tried a Round Robin OCW test yesterday on a new load for my .223 JP AR-15. I already have a good load for it now with XBR and 77 SMKs. But I wanted to work up a Varget and TAC load as I'm running out of XBR and it seems unobtanium at the moment, but I've got lots of Varget and TAC on hand. I'm not new to reloading, but I wanted to try the OCW method that is all the rage. I read Dan Newburry's page and followed the instructions to the letter to determine the powder starting charge and the increments. So here are the results.

Varget load w/ 77SMKs with 5 steps

TAC loac w/ 77 SMKs with 6 steps. I had to use the fouler target. But I did shoot a set of foulers on another target with TAC to get the barrel reset to the new powder.

These were all shot in a round robin style just as the OCW instructions suggested.

My previous method of finding the "node" was to shoot 5 shots groups @ 100yds of each powder step over a chrono and compare group size and ES/SD and then go back and reshoot the ones that looked to shoot well adjusting the seating depth up and down. It always seemed to work well for me in the past. I understand that the OCW method uses neither chrono data or group size to decide on the OCW, so I'm totally confused as to which of these groups the OCW camp would choose and more specifically WHY?

Thanks in advance.

 

[spife7980]

23.4-23.8 of varget are all impacting in the same relative area at the top of the diamond in relation to the point of aim. So if it gets hot or cold or you throw powder a tad high or low it wont change where the rifle is actually aimed and the bullet is going to go.

So I would take that 23.6 right in the middle of the range and work on the seating depths to try and time the bullets exit from the barrel to get it to group small.


For the TAC loads Im seeing that 23.8-24.2 are all about the same position as one another so I would look into that area with seating depth as well.

 

[padom]

Varget 23.5-23.6.. Even though the group is not small, the center of that 23.2 group is very close to the rest so I would say your node is wide from 23.2-23.8 and would go with 23.5gr but 23.6 good too.

 

[308pirate]

understand that the OCW method uses neither chrono data or group size to decide on the OCW, so I'm totally confused as to which of these groups the OCW camp would choose and more specifically WHY?

Thanks in advance.

Dan Newberry explained that very well. I suggest you go re-read his material more carefully this time.

It's all there.

 

[Gustav7]

It always seemed to work well for me in the past. I understand that the OCW method uses neither chrono data or group size to decide on the OCW, so I'm totally confused as to which of these groups the OCW camp would choose and more specifically WHY?

Thanks in advance.

Its all based on POI... If two different charge weights, lets call them 30gr and 30.5gr, impact at the same POI, that means that even though theres a difference in charge weight, the bullets still hit the same spot. That translates to distance as well... and allows a charge weight to be more forgiving because a mild change in powder/velocity doesn't change the POI as much, resulting in better precision between shots.

Heres a diagram.... The little triangles are the 3 shot groups. See how each target has a different POI, but then two targets in a row are the same.... Those two charges would be your NODE (30-30.5gr)... the OPTIMAL charge would most likely be in the middle, lets say 30.2-30.3gr.

 

[ReaperDriver]

Dan Newberry explained that very well. I suggest you go re-read his material more carefully this time.

It's all there.

Awesome, thanks for your help! I would never have thought of that on my own.

 

[ReaperDriver]

Its all based on POI... If two different charge weights, lets call them 30gr and 30.5gr, impact at the same POI, that means that even though theres a difference in charge weight, the bullets still hit the same spot. That translates to distance as well... and allows a charge weight to be more forgiving because a mild change in powder/velocity doesn't change the POI as much, resulting in better precision between shots.

Heres a diagram.... The little triangles are the 3 shot groups. See how each target has a different POI, but then two targets in a row are the same.... Those two charges would be your NODE (30-30.5gr)... the OPTIMAL charge would most likely be in the middle, lets say 30.2-30.3gr.

View attachment 7440168

Ahhhhh, Ok that's actually making sense now. So it about where different charge weights impact relative to the POA rather than the group size itself. That was my initial observation on the Varget string above, was that they all wanted to impact at the 12 o'clock tip of the diamond. I think my issue was I wasn't seeing as much of a "scatter" as your drawing above shows, but that makes sense now. Huge thanks.

 

[ReaperDriver]

23.4-23.8 of varget are all impacting in the same relative area at the top of the diamond in relation to the point of aim. So if it gets hot or cold or you throw powder a tad high or low it wont change where the rifle is actually aimed and the bullet is going to go.

So I would take that 23.6 right in the middle of the range and work on the seating depths to try and time the bullets exit from the barrel to get it to group small.


For the TAC loads Im seeing that 23.8-24.2 are all about the same position as one another so I would look into that area with seating depth as well.

Cool, thank you! I will get working on those. I was initially disappointed in the TAC performance, but it has worked well in previous precision AR's, so I'm sure with some tweaking it will come down.

Presumably with OCW, it will in theory account for Hot and cold changes throughout the year if a given powder is sensitive to temps (for instance TAC)? Correct?

 

[308pirate]

I would never have thought of that on my own.

Seems like you should have. Learn better that way

 

[Gustav7]

Ahhhhh, Ok that's actually making sense now. So it about where different charge weights impact relative to the POA rather than the group size itself. That was my initial observation on the Varget string above, was that they all wanted to impact at the 12 o'clock tip of the diamond. I think my issue was I wasn't seeing as much of a "scatter" as your drawing above shows, but that makes sense now. Huge thanks.

Unfortunately its never as easy as the diagram I drew LOL... I wish it was.

It's one of the downsides and criticisms to the OCW method is that it's often hard to interpret. Also, if you throw a flyer and aren't experienced enough to know you threw it, then it affects the center of that group.

 

[spife7980]

Presumably with OCW, it will in theory account for Hot and cold changes throughout the year if a given powder is sensitive to temps (for instance TAC)? Correct?

Thats the hope at least

 

[ReaperDriver]

Awesome, thanks for your help! I would never have thought of that on my own.

Seems like you should have. Learn better that way

Well, given that I did re-read DN's site 2x and still didn't get it, that's why I posted the question. Last I checked, this was a "discussion" forum. You know, that place where people discuss stuff and ask questions and some people are nice enough to try to help. I wasn't aware this was the "Go take your questions, GTFO and go back and re-read your texbooks" site. Because in reality, EVERY question ever asked already here has the source info out there somewhere. Sometimes, something obvious to one person, isn't to another. Hence why we actually "discuss" (Damn, I used that word again) stuff.

I dunno, maybe you're just having a bad morning. Maybe the Wife yelled at you on the way to work or you just found out your teenage daughter was pregnant or your son was gay. So I'll give you the benefit of the doubt and resist the urge to just call you a dick. So I won't. Hope your day goes better sir. Take care.

 

[ReaperDriver]

Varget 23.5-23.6.. Even though the group is not small, the center of that 23.2 group is very close to the rest so I would say your node is wide from 23.2-23.8 and would go with 23.5gr but 23.6 good too.

Cool, thank you. I'll work on refining that bracket.