Help with OCW Test - 308 RPR & XBR8208

M

macsailer

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As per the title, looking to the forum for some help doing the OCW test. I followed the instructions to a (pretty much) tee, and now need some help diagnosing the resulting targets. All groups shot out of a Ruger Precision Rifle calibered in .308.
Case = Lake City Brass, Full Length Sized, Trimmed to 2.005"
Primer = Federal 210M
Powder = IMR XBR 8208
Projectile = SMK 175gr

All shot off a bench, bipod in front, caldwell bean bag in the back.

P1010739.jpg


P1010740.jpg


Based on the results, I think loading and playing around with CAOL with powder charges around the 41.7gr to 42r mark will be the key. Am I on the right track?

Mac
 
Yes you're on the right track.

Are these 100yd groups?
If they are, I'd strongly suggest stretching it out. More distance, more info.

With your testing, as long as you're not flirting with pressure, keep on going. I think you're missing out on something.
Look at horizontal of 42.3 then 42.6.
Tell me you can't claim the low shot on 42.6 ;). I'm curious how a 5 round group would look.

If those were my results, I'd keep on going. Again, provided pressure isn't an issue.

What was your sight load?

* careful taking interweb advice
 
Did you shoot round robin or was it 3 consecutive shots of each load on each target?

I think you are on the right track. I'd try different OALs at 41.9 grains.
 
I'd go to 41.6gr and 42gr in 0.1gr increments. 5 groups of 5 rounds each.
Go from there... Then when you get the powder charge start playing with OAL. That is what I'd do... But I've only been reloading since September 2015 ~2000 308 rounds w/ 175 smk's and gm210m primers.
 
9x19p said:
Yes you're on the right track.

Are these 100yd groups?
If they are, I'd strongly suggest stretching it out. More distance, more info.

With your testing, as long as you're not flirting with pressure, keep on going. I think you're missing out on something.
Look at horizontal of 42.3 then 42.6.
Tell me you can't claim the low shot on 42.6 ;). I'm curious how a 5 round group would look.

If those were my results, I'd keep on going. Again, provided pressure isn't an issue.

What was your sight load?

* careful taking interweb advice
Click to expand...

Thanks for the advice! No pressure signs. Lol re the 42.6gr shot. It was cold outside, and I may have rushed it a bit, and I had to get home so I didn't get in too much trouble! I will work up to higher pressured.

Pr589 said:
Did you shoot round robin or was it 3 consecutive shots of each load on each target?

I think you are on the right track. I'd try different OALs at 41.9 grains.
Click to expand...

I did not shoot round robin, which I now realize I should have done. Is there a large difference between the two?


bsand said:
I'd go to 41.6gr and 42gr in 0.1gr increments. 5 groups of 5 rounds each.
Go from there... Then when you get the powder charge start playing with OAL. That is what I'd do... But I've only been reloading since September 2015 ~2000 308 rounds w/ 175 smk's and gm210m primers.
Click to expand...

Awesome, thanks! What powder are you using?
 
Re-read Newberry's OCW test instruction again. Triangulate the shots and find the closest POI for three consecutive powder ranges. If you didn't shoot it round robin like the instruction say then it will depend upon the time difference and if you let your barrel cooled before you shot your next group it might affect the outcome. OCW will be subjective and closest POI for several group be dependent on interpretation.

Download this OCW calculator it's very helpful and breaks down steps you need to get to your final OAL test.
http://ammoguide.com/myag/articles/downloads/OCW_Workup_Calculator.xls

original thread:
http://www.canadiangunnutz.com/forum/showthread.php/1258086-Optimal-Charge-Weight-Worksheet-FYI

Good luck! OCW method works I've had success in a variety of cold and hot conditions during f-class competition and groups always come out consistent regardless of temperature.

If I had to triangulate the POI of three powder groups I would estimate powder charge 3,4 &5 to be similar in POI. Powder charge 4 would be where you do your seating depth test.
 
Last edited:
I like to plot the average POI on a Cartesian plane and look for the "loop". But I think you are on the right track with your observation.
 
Off to a great start... given Hodgdon load data, you are pretty much on or slightly over book max.

I too would suggest retest from 41.5 to 41.8gr.... 42 to 42.6gr is classical sign of load pressure getting too high... lots of tempting clusters with significant outs. 42.6gr is way out of tune and vertical stringing is occuring.

So tempting but I bet you find no consistency at this load point.

Note: the OP is using LC brass which is heavier then Win used in the load data... so he is using an effective higher charge.

Nice start... enjoy. Do redo test further away - 200 or 300yds. Things will become very clear. I wouldn't bother with OAL as your mag dictates what you need to use.

Work towards accuracy with consistency.

Jerry
 
Thanks to all who have taken the time to respond thus far. I think all of this has confused me greatly.

I have broken out my Hornady measuring tools, and am now a bit stumped. The rounds which I loaded were loaded to a CAOL of approximately 2.82". When measured with the OAL tool, these measure approximately 2.33" long, from base of cartridge to 175r SMK ogive.

I then use the other Hornady tool, and I measure the distance to the ogive in the gun. I did it 10 times, by average is ~2.250". According to this, I infer that the bullets used in the original rounds used to conduct my OCW test were jammed into the lands.

Am I on the right track?? If so, I think that I should re-do the OCW test, this time, seating the bullets at, or under, the lands. If I place it right at the lands though, this will result in a CAOL of 2.74". This seems really short to me.

Thoughts? Thanks guys.
 
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