My OCW Test

[Berto]

37.6 shot again

[tom604]

should of tried 36.8 or 38 again as well, if it was the heat that caused the spread on 37.6 and then it tightened up that much those two groups should pin hole
what rest were you using ? did you try any other loads? nosy bugger arn't i

[sungazer]

Should of shot the 37.2 again if you were the fault of the horizontal at 37.6 it was probably the same fault at 37.4 other have said go for the outlies due to better looking groups again I would suggest you go for the mid range 37.4 as you have good groups on each side, where fliers are less likely to happen. You can see what I meant about the true results getting lost in the noise of errors.

[Berto]

37.8 shot similar to 37.6 in the retest, 37.4 had a bit of verticle spread but im blaming that on me.

I think ill be trying some seating depths at 37.6 as it appears i have a rather long node and it is rather stable either side

[bladeracer]

I have since reshot the grp at 37.6 and there is far less horizontal spread

That's exactly why I wouldn't be making these decisions based on three rounds of each load.
How do you know the other groups are truly indicative if you haven't shot any more than those three rounds?

[sungazer]

The theory is that charge weight is only responsible for vertical spread. The ability to group is all based on seating depth. A lot of people will only shoot one shot at each charge normally a bit closer together based on others experience or velocities wanted. then a flat spot selected and that charge weight then shot at different seating depths to look for grouping. Lots of theories out there with some guns you cant afford to shoot lots in load development unless you purchase 6 barrels and have them all chambered at the same time and then also grade barrels.

[bladeracer]

The theory is that charge weight is only responsible for vertical spread. The ability to group is all based on seating depth. A lot of people will only shoot one shot at each charge normally a bit closer together based on others experience or velocities wanted. then a flat spot selected and that charge weight then shot at different seating depths to look for grouping. Lots of theories out there with some guns you cant afford to shoot lots in load development unless you purchase 6 barrels and have them all chambered at the same time and then also grade barrels.

True, but if you own a rifle like that it generally drops all the bullets through one hole so you don't need groups to know where it's shooting.
If you can't shoot that consistently though then you need to shoot a much larger sample to determine the potential of each charge weight - including horizontal and vertical displacement.

[marksman]

this is a true OCW test
what Apollo is referring to is the Audette ladder system
I recon your pretty close with what you have

[Gwion]

I'm with Brett. Load up a bunch at 36.8 and 38 to confirm. Personally the 38 looks the best but not enough data to know for sure. You need a few more 5 round groups to get a good indication. Some times you fluke a good group just like sometimes you shank a flyer. That is, it's not uncommon to actually pull a shot into the group that would have been a flyer if your aim was true.
Numbers count when it comes to averages.

[straightshooter]

This whole exercise seems like a waste of time to me. Similarly with some of the attendant advice offered.
So the rifle is intended for hunting, right.
Shoot a numerically significant group, like at least 10 shots, at 200 yards or meters or at your preferred zero range depending on what you have access to.
Then adjust your scope to correctly center it for that group and your desired trajectory.
Then fire a confirmation group.
If the confirmation group shows that you have done things right and provided you don't do any further tinkering, then you can happily pack up and proceed to a successful hunting career.
Don't give a second thought at all to the actual group size because in reality, over a sufficiently large sample size, no amount of minor tinkering will improve it.
An appreciation of statistical analysis would help to grasp why.
Unfortunately many people cherry pick and fall in love with factors they believe will improve accuracy while ignoring or being totally ignorant of other factors that swamp the effects of their preferred minor adjustments.
In your case for example you have chosen 2208 for a 75 grain projectile in a 243. This results in a loading density of at best about 80%. You will thus inherently have significantly greater variations in ignition and pressure and chances are that this will overwhelm the effects of tinkering with minor variations in charge weight or seating depth.

[in2anity]

Did you have few minutes break between groups? What sort of rest were you using? Did you only shoot a group of 3 per increment? Was there any wind? Are you a good shot?(I.e. can you rule out human error)

Point is, IMO three shots per increment is not a big enough sample size to identify trends. I say run the test again and see if the results are the same. And then do it again, even try 5 shot groups.

[marksman]

I'm usually cocky enough that if when I do an OCW test if 2 holes are way apart I wont shoot the third and move to the next
saves my barrel life, I never do more than 3 shot testing, if it don't work for 3 shots its not going to for 5 or 10
when finished and have decided what I want to explore I will definitely reshoot what I call the OCW as well as just above and just below to verify the OCW
exactly how you are supposed to do when doing an OCW, there is usually more than one load you would want to explore
I have seen too many people who don't verify then call the OCW a waste of time when there load does not perform
after shooting this load for a while you will need to retune your loads as well as retweek your rifle, its called maintenance

[tom604]

seems a waste of ammo but each to their own

[in2anity]

seems a waste of ammo but each to their own

Nope for trend analysis, the larger the sample size the more acurate your trend identification will be. Three shots per increment is NOTHING. But as BF has already said, if this is not for competition, there’s not a huge reason for getting caught up on the details. Find a decent enough load and go out and shoot!

[tom604]

seems a waste of ammo but each to their own

Nope for trend analysis, the larger the sample size the more acurate your trend identification will be. Three shots per increment is NOTHING. But as BF has already said, if this is not for competition, there’s not a huge reason for getting caught up on the details. Find a decent enough load and go out and shoot!

but he had two groups that were better than what he was looking at and then he was going to have to play with the seating to get it to group
three shot is the min for an average,the more you shoot the better the info

[bladeracer]

seems a waste of ammo but each to their own

No shooting is a waste of ammo in my book, it's all good

[Daddybang]

No shooting is a waste of ammo in my book, it's all good [/quote]

I don't understand most of the technical sh@t being discussed ...but this I get!!!!

[tom604]

seems a waste of ammo but each to their own

No shooting is a waste of ammo in my book, it's all good

true that better if it's at a critter

[sungazer]

Just another part of the load development which I think affects group size more under most conditions is seating depth. In the picture below I started with seating depths of what I thout was on the lands then at 15 thou off,25,35,50 and 60. After looking at the results I when back and decided to try harder and be more precise with my 0 or on the lands seating and removed the ejector spring in the bolt to get a better feeling. The reason for this was that the 25 thou off if it was that didn't fit the pattern I would expect. As it turned out I was correct and the 25 thou was some touching and some not. There is about 4 thou tolerance in seating the bullet. and the 0 and 15 were in fact jammed.
Anyway I adjusted the dies and decided to re run the tests. These are all using 308 Berger 155 hybrids. I would have liked to see the point in which the groups opened up it looks like the Hybrids are very tolerant to seating depth. I did the second test at 0,20,40,60 and 80 thou off the lands. The second test are the groups on the top.
From this I think I will seat them 50 thou off as 40 and 60 are pretty good and that gives room for any tolerance issues.

IMAG0197.jpg

I was also testing a firm recoil hold vs a free recoil the first groups shot free recoil then I shot a group the same day in the bottom middle using a firm recoil hold and found it was not any worse but keeps the rifle more on target. The second test was all done with a firm recoil hold. Just to see if any more fliers appeared. It is important to keep the conditions all the same as there is a difference in POI from free recoil to soft hold to firm hold to grip as hard as you can.