OCW opinions...?????

[Kampfjager]

If I am understanding this correctly, then, the shooter is trading off a little bit of group size for a more stable POA, i.e. less dependent on charge weight? Again, just asking . . .

Yes, if the group size is good but poi isn't stable it will open up and be all over the place at long range distances, usually vertical dispersion will increase exponentially..... if group size isn't satisfactory then ya need to look at different components, i.e. bullets.........

 

[Ga6570]

If I am understanding this correctly, then, the shooter is trading off a little bit of group size for a more stable POA, i.e. less dependent on charge weight? Again, just asking . . .

Correct, after the similar POA is determined, then the reloader, makes adjustments to other items like seating depth...

Basically to start this method a loader would choose the components ie powder, bullet, primer, brass. Then using published data determine where to start with load charges and load some up and run it through the test. Anywhere from 6 to 12 different charges is my preference. The number of different loads is determined by the person loading. After shooting a round they may decide the selected powder or charges don't give them what they are hoping for and may start over if the results don't prove much. IMHO That is why OP is asking here. He's not seeing exactly what he hoped for and doesn't want to start from scratch again, but asking for help with making a decision...

 

[Ga6570]

I'm assuming you'd be in the area of 45.5 also?

Yes I think the tops ones are all very similar POI related to the POA so - 45.5 or 45.7 is where I'd do some more testing.

 

[Kampfjager]

Ga6570, you are correct.... it's a hard test to read and I believe a different bullet would be an optimal improvement

 

[User4302021]

I recently did a seating depth test with a custom 308 @ 100 yards. It was a trued Rem700 with a 24 inch Bartlein 1/10 twist and a match chamber. The chosen load was 41.4 grains IMR4895 in LC 11 LR brass and 175 Nosler RDF's, chosen by the OCW method.

All brass was identically prepped and properly annealed. The rifle was shot off of sand bags from an extremely stable position and barrel was allowed to cool between groups.

Group size and shape means exactly nothing when doing the OCW.

 

[User4302021]

I don't fully understand Dog Rocket's analysis, so I am just trying to learn by asking questions: To me, it looks like the 45.5 gn is the worst group in the series. Why would it be selected as the one to do seating depth tests? Wouldn't it be best to choose the tightest group to fine tune for seating depth? Sorry if this is a dumb question, and, again, just trying to learn.

Check out post #61 for the answer.^^^^^

 

[shinbone]

View attachment 130609 Group size and shape means exactly nothing when doing the OCW.

So, again, if I understand correctly, choosing the optimum charge weight is based almost solely on a stable POI, as determined by distance and angle from POA from group-to-group. Once the optimum charge weight is determined, group size is then minimized by adjusting seating depth.

And, this is done to arrive at a very repeatable POI; with a reasonably small, but not necessarily the smallest, group size.

Correct?

 

[User4302021]

15 shots @ 200 yards with the same load above @ 2.815"COL.
The 2 shots up top are uncalled fliers. The 1st shot, which is circled, belongs in the group. A 0.4 mil correction was made to keep the group away from the edge of the paper.

Notice that the body of the group is round, And 13 of 15 shots, center to center, measures right at 1.5", so right at 3/4 moa.

 

[User4302021]

So, again, if I understand correctly, choosing the optimum charge weight is based almost solely on a stable POI. Once the optimum charge weight is determined, group size is then minimized by adjusting seating depth.

And, this is done to arrive at a very repeatable POI; with a reasonably small, but not necessarily the smallest, group size.

Correct?

Yes, a stable POI is the main goal of the OCW. The group size will be the smallest over time, but not necessarily at that time. What a particular load does for one time on a particular day is meaningless. It is the performance over time and a variety of conditions that matters.

 

[Kampfjager]

And it will be the smallest group possible at further distances due to it being very consistent...... and will be consistent over a broad temp range also

 

[shinbone]

15 shots @ 200 yards with the same load above @ 2.815"COL.
The 2 shots up top are uncalled fliers. The 1st shot, which is circled, belongs in the group. A 0.4 mil correction was made to keep the group away from the edge of the paper.

Notice that the body of the group is round, And 13 of 15 shots, center to center, measures right at 1.5", so right at 3/4 moa.

Okay, now I am confused, again: why are the two fliers excluded from the measurement?

 

[Ga6570]

Link to the instructions on the method...

http://optimalchargeweight.embarqspace.com/ocw-instructions/4529817134

 

[User4302021]

Why are the two fliers excluded from the measurement?

Given the size and shape of the sampling, along with the relative distance from the body of the group, it can safely be deduced that something was abnormal about them.

If the load was to blame, the group would have been much more random. The Nosler RDF's are pretty notorious for this and I kind of expected it to be honest. But they have a high BC and the seconds are cheap. For cheap practice, I can live with the occasional flyer.

This is why I confirm a load at 200 yards and typically use 15 to 20 shots (groups of 5 at a time at the same point of aim). At 200 yards, any factors that were living inside the statistical noise at 100 yards tend to make themselves known. Yet 200 yards is still close enough to control or account for environmental conditions.

 

[shinbone]

Cool! Thanks!