OCW load development

DsrtRat

DsrtRat

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I thought I would try some 65 gr Sierra's in my 12 twist 223 today. I have been reading the optimal charge weight info and figured I would give it a quick try.

I wasn't sure if the gun would shoot the 65 grainers very well. I started with the a 24.5 gr charge increasing at .3gr per jump up to 26gr (26.4 being max in my book). I only made up 3 shells of each powder measurement.

Conditions. +15c, 10 mph wind quartering from behind.

This gun will shoot .3moa or better with 50gr NOS BTs if I do my part. here is a picture of the results for my 6 different loads. I would shoot 3, let the barrel cool, then shoot 3 more. With 6 different loads, my shot sequence was:

123 cool 456 cool
234 cool 561 cool
345 cool 612 cool

I know that I should be looking for the string of bullets that impacted in the same spot to find the node where the barrel is less active but the tightest groups seemed to be on the fringe of that.

If using the OCW method, how does one interpret this? To me, the group is slowly moving from left to right as the charge is increased with decent groups at 24.5, 25.4 and 26 grains of Varget. ANyone wanna take a stab at howto read these results?

65sierra.jpg
 
Isn't it the two groups bigger than the scatter group? So if the scatter group is 25.7, then the next two up would be the money loads? Load development is complicated, I don't understand it that well.

Great shooting BTW.
 
OCW really needs more range than 100 yards. I would repeat the test at 200 or better yet 300, and see what that does for you. I wouldn't think the 1-12 would be able to properly stabilize a 65gr bullet and 300 yards might prove that theory. If you aren't getting pressure signs at 26.4 I wouldn't be afraid to go higher next time as well. I am currently developing the EXACT same load as you in a 1-9 twist. I am up to over 27.5 gr with pressure signs just developing.
 
With .223, you really should use 0.2gr. jumps. That 0.4gr. jump at the end is much too big.

Looks like there may be a scatter groups at 25.2gr. I would repeat with 25.0, 25.2, 25.4, 25.6, 25.8, 26.0, 26.2, 26.4

OCW only needs to be run at 100 yards and you ideally want no wind. If there is wind, it needs to be very constant.
 
Thanks for the info. This was just the start to see if the gun would even shoot the 65 gr bullets. It appears to be able to shoot them (at 100 yards anyhow).

I will experiment with loads quite a bit more to find the sweeeeet spot.

I went backand read the OCW thread and yeah, the scatter group appears to 25.7gr.. I think I will repeat the test with smaller jumps. I have to admit that I was short on time and empty brass when I did this. I was more interested in seeing if my 12 twist would stabilize a 65gr bullet but find the results and further experimentation to be very exciting.

Is there usually only one scatter group or do you pick the biggest spread? Seeing that I used a .3 jump in powder, to me it looks there could be another scatter at 25.1gr.

I am starting to show what looks like some high pressure signs at 26gr. The primer dents are quite a bit deeper than normal and have a moon crater look to them with a raised ridge around the firing pin circle. I have some room to seat the bullet deeper though and increase the free bore and hopefully stay away from the high pressure.
 
Sometimes the scatter group shows up in two of the steps. And if you're doing a large charge range, you will likely find more than one OCW node. So, there will be more than one scatter groups. You want to pick the highest one since the velocity will be higher.

The scatter groups should always be followed by two or three groups that fall in the same x-y location relative to the point of aim. That is the pattern you are looking for...
 
Ahhh, now I am starting to see the light.

Thanks

Question about pressure. My primers were showing a little bit of pressure compared to my 26.5var behind 50gr NOS Bts. The strike was deeper witha fine ridge around them. No primers popped out and the headtsamp is not showing any signs of overpressure.

I seated the bullet at 2.331 which is well off the lands but the books suggest OAL of 2.20-2.25 (depending on the book). If I seat the bullet deeper, will the pressure decrease due to the free-bore space beofre I am into the rifling or will pressure increase due to the smaller space in the case?
 
I am using CCI primers. They don't look any flatter than my previous primers on different loads. The headstamps all look normal and are well within spec for width.

One thing I noticed was that the bolt was a little tough to close with these loads. I was using once fired and then full length sized brass. I just tried some of the same brass that had been sized but not loaded and found it tough to close the bolt so I suspect I was not setting the shoulder back enough. I reset my die and started moving it down very small increments at a time until I the brass fit in the gun much easier. I will go out shoot some more and see what happens.
 
Group size can be modified later using seating depth. What you want is to find the 3 charge weights who's average POI are the closest. The middle charge is your OCW. Then tinker with seating depth to get your load dialed in. Looks like 25gr is your OCW, and now it's time to play with COAL for fine tuning.
 
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