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Quickload and OBT

Bill.

I got it,
THANK YOU,
That saves a lot of work. ;D

Now, if the blasted wind will quit blowing, I test some loads, I hope.

Tia,
Don
 
Busdriver said:
Erik Cortina said:
Nomad47 said:
If you shoot a lighter bullet, obviously MV increases decreasing barrel time, so you might try to hit node 3. But if you run into pressure signs before hitting node 3 you would have to settle with node 4.

Not true, that's why when you asked me if I use the OBT theory I said not anymore. I do use it, but sometime have to modify it such as in this case.

I have won matches with a gun shooting in between OBT nodes.

Me too! There are "half nodes" as I like to call them. If you look at Chris' nodes, they are about 200-250 fps apart in the 308. Most experienced competitors will tell you that nodes tend to be 100-120 fps apart. As such, there has to exist good shooting combinations approximately half-way between OBT nodes. I have proven their existence, but what I can't prove is whether they are as good of nodes as the ones Chris determined.

My guess is that if you think you are shooting between nodes, your QL setup may be off. I've thought I was between nodes before, only to find that I did not account for seating depth changes (Cartridge Length in QL), case length, maximum case capacity, etc... If I find myself drifting off a node (according to QL), I usually go recheck all of those things and so far, it's always sync'd back up.
 
In my view, there are three factors that must align to produce an accurate, reliable, long range load, assuming that the rifle, ammunition, etc. are top quality. The three factors are: [br]
Combustion characteristics - This is affected by powder, charge weight, primer, bullet weight, seating depth and case design. The idea, of course, is to reach minimum muzzle velocity variation. [br]
Barrel time: My best loads are always very close to a correctly calculated OBT node. [br]
Barrel harmonic characteristics: This will strongly affect group size and consistency. Seating depth will usually bring this into line but, not always. A reasonably certain way to align barrel harmonics is to use a tuner.
 
jaychris, to add to what you posted.

A couple days ago I shot my new 6SLR barrel for the first time. I used QL & OBT to come up with some loads. I also adjusted Powder Ba from experiences with a similar cartridge. I loaded four different powders, two charges each, one charge 1.5 grains under an expected OBT node and the other charge .5 grain under. I wanted to use these charges with MV readings to "calibrate" QL.
IMR7828ssc was very interesting. The lower charge had 3 of 4 touching with the first shot 1/4" away and it was from a clean bore. The higher charge had severe vertical stringing (2" spread at 100 yds). After "calibrating" QL, I found the good group to be dead on a node that included the brake in the barrel length measurement. And the bad vertical group was EXACTLY halfway to the next node.

Edit: I should explain that the brake issue has happened to me on one or two other barrels and I can't explain why. But I enter the bolt face to crown length for barrel length in QL. But when calculating OBT nodes bolt face to end of brake is used. Sometimes it works and sometimes it doesn't work.
 
What would happen with an adjustable muzzle break, aka, Boss type system, only using a 3 to 5 gill slot type MB, as to not blow up dirt etc when shooting prone?

I have over .700" of adjustment using the above system.

My thoughts/thinking on this, is to set this system at the minimum adjustment range, find a good load using all the 3 most important facts, (as I understand them), Combustion characteristics/QL + OBT + adjusting the Barrel harmonic characteristics using the adjustable MB, then I would have the +700" of adjustment, if needed.

Thoughts or comments?

Bill,
Thanks for the info on the OBT/MB, as none of my bbls fall into the even inch or 1/2" marks, now I can enter the decimals and get it closer. I was wondering about that info.
Tia,
Don
 
My muzzle brakes have maximum contact with the barrel and are as close to being part of the barrel as you can get. When I look for OBT nodes, I use bolt face to crown for one set of nodes and bolt face to end of brake for another set of nodes. And I suppose a person could have a third set of nodes depending on what is on the end of the barrel.
One thing is constant, though - on QL, barrel length is one number, bolt face to crown.

One thing I have never quite understood. Chris Long speaks of a "swell" traveling up and down the barrel and that you definitely don't want the bullet to exit the barrel when the swell is at the crown. So it would seem to me that it is more important to avoid the midpoint between nodes than it is to hit right on a node.
We have quite a few very bright individuals on this forum. Maybe one or more of them can explain this.
 

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