Long range load development at 100 yards.

[Erik Cortina]

so would he chose 46.5 gr?

46.5 is right.

 

[Erik Cortina]

I usually find that jam -.020" shoots good with most bullets, so I start there.

For testing, I start at Jam -.010" and work away from there in .003" increments.

Erik, what made you decide to use .003 increments? Do you see significant changes in tune during the testing of different seating depths? Once you have determined your optimum OAL do you vary this length during the life of the barrel?

Thanks,
Andrew

Seating depth nodes are .003" apart. Most people do .010" tests and skip over the nodes.

I chase the lands for the life of the barrel.

 

[Erik Cortina]

Erik:
Would be interested in your opinion of the effect the magneto speed chrono might have on your method of arriving at the optimum load/node? As you know the front bayonet measurement device affixes to the barrel and does effect poi mostly in the area of elevation in my experience.
Also, is finding a "flattening of the speed" more noticeable using .05 incremental increases vs .02?

Anything you attach to the barrel will affect POI and accuracy. That's how barrel tuners work.

You can use .2 gr increments, but it's faster going every .5 gr.

 

[tonysnoo]

I usually find that jam -.020" shoots good with most bullets, so I start there.

For testing, I start at Jam -.010" and work away from there in .003" increments.

Erik, what made you decide to use .003 increments? Do you see significant changes in tune during the testing of different seating depths? Once you have determined your optimum OAL do you vary this length during the life of the barrel?

Thanks,
Andrew

Seating depth nodes are .003" apart. Most people do .010" tests and skip over the nodes.

I chase the lands for the life of the barrel.

What do you mean, you chase the lands? Does the same seating depth work in reference to the throat erosion....In other words....longer oal as the barrel wears?

 

[Erik Cortina]

What do you mean, you chase the lands? Does the same seating depth work in reference to the throat erosion....In other words....longer oal as the barrel wears?

Yes. As long as you keep the same seating depth in relation to the lands the barrel will continue to shoot unless you get too far out to where pressure will decrease enough due to extra case capacity to put you outside the node.

 

[palo]

Erik
By only adjusting seating depth by .003 at a time how many loads on average does it take for you to find best accuracy ?

 

[Beau]

OCW article:

http://optimalchargeweight.embarqspace.com/

That seems awful complicated when you can just watch your chronograph and see when the velocities flatten out.

My velocities have never flattened out. They keep on increasing until the bolt gets really hard to open.

If you graph velocity you'll see a point where you aren't getting as much of an increase in velocity per unit of powder.

 

[CatShooter]

OCW article:

http://optimalchargeweight.embarqspace.com/

That seems awful complicated when you can just watch your chronograph and see when the velocities flatten out.

My velocities have never flattened out. They keep on increasing until the bolt gets really hard to open.

If you graph velocity you'll see a point where you aren't getting as much of an increase in velocity per unit of powder.

I'm sorry, but where did I say I never graphed anything?

I've been doing this stuff for close to 50 years, and work in a ballistic lab.

I have graphed this stuff hundreds of times and see none of this "flattening"

 

[Beau]

I always see it. YMMV, apparently.

 

[Erik Cortina]

CatShooter, the velocity curve will not flatten, but the speed will increase less per .5 gr of powder.

For example, on my 7mm FCM the ES for .6 gr of powder is 35 fps.

 

[Erik Cortina]

Erik
By only adjusting seating depth by .003 at a time how many loads on average does it take for you to find best accuracy ?

It takes about 8 groups. I usually go from jam - .010" to about jam - .030" and it will show about two nodes that will shoot for you.

 

[Erik Cortina]

Someone asked that if the speeds don't flatten out but the groups do what do you do?

Well, I always trust the target more than the chronograph. So, go with the loads that flatten out and then adjust seating depth. Many times, ES will improve after you tune your seating depth.

 

[DennisH]

Well, I always trust the target more than the chronograph.

Erik, do you still check your final load choice and compare it with your chrono readings?

I do agree, the target gives the facts.

Dennis

 

[CatShooter]

CatShooter, the velocity curve will not flatten, but the speed will increase less per .5 gr of powder.

For example, on my 7mm FCM the ES for .6 gr of powder is 35 fps.

The reason for that is that "speed" is not in direct coloration to powder weight, it never is... energy is the important relationship.

If you double the powder, you do not EVER get double the velocity - to get that, would mean that you had created 4 times as much energy from twice the powder - Einstein says that is impossible, and I tend to agree with him most of the time.

If you believe that velocity increases in direct proportion to powder weight, then you do not understand internal ballistics.

The velocity increases by the square root of the percent of powder increase.

It just is.

If you can prove otherwise, I would strongly suggest that you write it up and submit it to the Noble Prize Commitee in Norway - department of Physics. If you can prove it, I assure you that you are a shoe-in for a Noble Prize (worth $1.3 million) and you get a collage named after you.

 

[Steve Blair]

Here's an example from .300 WSM load development. From 68.4 to 68.7, there was little velocity change. Velocity had been climbing incrementally up to 68.4, when it flattened. Lowest ES also occurred at 68.6 and then rose quickly after 68.8 as pressure approached maximum. [br]
I later shot five 5-shot groups of 68.6 and 68.7 and confirmed this series. This is typical in my load development of several cartridges.

 

[Erik Cortina]

CatShooter, nobody said that speed will double if you double powder charge.

Steven Blair chart shows what we have been talking about.

 

[Dgd6mm]

Erik,
Bravo on your thread, great information. This request is a little off topic, but could you post your brass and bullet prep procejure before you start to test? Providing that there is any, which I assume there is. I'm just trying to get MY DUCKS in a row to build the most accurate ammo that I'm capable of.

Thanks.
Don Dunlap

 

[Erik Cortina]

Erik,
Bravo on your thread, great information. This request is a little off topic, but could you post your brass and bullet prep procejure before you start to test? Providing that there is any, which I assume there is. I'm just trying to get MY DUCKS in a row to build the most accurate ammo that I'm capable of.

Thanks.
Don Dunlap

Don, I will probably start another thread in the future about brass prep. Heck, I might do a thread on every aspect of precision reloading as I know it.

I believe the next one should be about finding the lands accurately though, as I see people are all over the place on this issue.

 

[trailrider121]

Erik,

I have been following this topic, and I must say it a great topic for long range loads. Can't wait to see your next post on hand loading.Great job!

 

[Erik Cortina]

Erik,

I have been following this topic, and I must say it a great topic for long range loads. Can't wait to see your next post on hand loading.Great job!

Thank you.