Ever have your accuracy node not line up with your powder node?

[Alex Wheeler]

Example, you test at long range and your shooting good vertical but each powder charge jumps in velocity, then you reach the powder node and velocity stabilizes and your groups print at the same poi but they are all vertical, as you leave the powder node the vertical tightens back up.

 

[BigDMT]

Happens all the time. Many top long range BR shooters dont even care about SDs. I talked to one of the best recently and he said he doesnt even get too worried about bullet runout as long as his gun shoots it

 

[Alex Wheeler]

So, are they just going with the load that groups, even though it will be touchy or are they going to the node and trying to tune it in with seating?

 

[josh.rizzo]

This is just my unscientific hypothesis, but I imagine that in an accuracy node, the velocity dispersion is lining up with the barrel harmonics. This theory would make sense if the node is in the middle of the barrel's upswing (while it is flexing from down to up).

So basically, if the velocity increases, the bullet leaves the barrel sooner and exits while the barrel is flexed down (below the center axis). This would lower the trajectory, compensating for the bullet potentially hitting higher form the increased velocity. If the velocity decreases, the bullet stays in the barrel longer and leaves on a higher axis, compensating for the lower POI from decreased velocity. I hope that makes sense the way I explained it. Anyone care to confirm or deny with evidence/science?

I always load to the accuracy node. I don't even pay attention to velocities until I have my load completely worked up, at which point I chronograph the load just to setup my ballistic calculations. I've had some loads with relatively bad extreme spreads that still grouped great.

 

[BigDMT]

I always load to the accuracy node. I don't even pay attention to velocities until I have my load completely worked up, at which point I chronograph the load just to setup my ballistic calculations. I've had some loads with relatively bad extreme spreads that still grouped great.

+1. Not sure if its the right way, but thats how I do it as well.

I always hear the guys Ive shot with talking about at which speed they find the accuracy nodes. Never at which speed they are trying to find accuracy.
Granted, certain speeds, depending on bullet BC, need to be reached for long range shooting, but accuracy is the name of the game.

 

[Steve Blair]

I always load to the accuracy node. I don't even pay attention to velocities until I have my load completely worked up, at which point I chronograph the load just to setup my ballistic calculations. I've had some loads with relatively bad extreme spreads that still grouped great.

[br]
At what distance are you shooting?

 

[mikecr]

If by 'powder node' you mean a charge amidst several in lower MV spread, why would this correlate to barrel tune?
It could, but there is no reason for it to. Hence tuners.

As implied already, barrel tune matters more, and seating matters more, and it's my contention that they are all independent of one another.

 

[Alex Wheeler]

I am shooting at 1k.
Yes, powder a node, where shots of slightly different powder charges hit the same poi, thats what you look for in a ladder test. MV spreads have nothing to do with it. Normally when I find that flat spot vertical tightens up, in this case it opened up. Shooting in the node is desirable to me as I will have some forgiveness in the load. Of course I will shoot it where it shoots best. Basically this is more of a theory question as I have never seen a barrel come into the node and shoot worse.

 

[Erik Cortina]

Load powder charge to where it's stable, them adjust seating depth. If still not happy with results after adjusting seating depth, get a barrel tuner to bring the groups in the rest of the way.

 

[josh.rizzo]

At what distance are you shooting?

For 223 in an auto-loader, I usually load test at 100 and shoot out to 600 with it. For 308 in a bolt action, I load test starting at 100, move to 200 for fine tuning, and shoot out to 1000.

At 1000 yards with 308, you can start seeing MV variations more, but I still think the advantage of the accuracy node outweighs it. That being said, I generally load my charges to +/-0.01 grains, so I rarely have a MV spread of more that 10 anyways.

With 223 I'm less picky when reloading. Still, I've seen MV spreads of over 50fps and I can still get 1st round hits out to 450+ yards.

 

[tclaunch]

Example, you test at long range and your shooting good vertical but each powder charge jumps in velocity, then you reach the powder node and velocity stabilizes and your groups print at the same poi but they are all vertical, as you leave the powder node the vertical tightens back up.

The very reason I NEVER use a chronograph till I`m done with load devopement.

 

[Alex Wheeler]

Example, you test at long range and your shooting good vertical but each powder charge jumps in velocity, then you reach the powder node and velocity stabilizes and your groups print at the same poi but they are all vertical, as you leave the powder node the vertical tightens back up.

The very reason I NEVER use a chronograph till I`m done with load devopement.

I did not even need the chronograph to tell me there was a node there. When every .3 the group goes up 5-6'' then you hit the node and the next charge goes down 1.5''

 

[Terry]

This is an interesting thread. Are you saying a load with a 30 SD can shoot tighter than a load with a 9 SD without a barrel tuner?

 

[Erik Cortina]

This is an interesting thread. Are you saying a load with a 30 SD can shoot tighter than a load with a 9 SD without a barrel tuner?

Yes, they can. I have actually had a barrel that had and ES of 40 that would shoot great at 1000 yards. The problem was, that it would not shoot good at all at 300 yards.

Low ES will get you consistent accuracy all the way from 100 yards to 1,000 yards.

 

[Alex Wheeler]

Eric, I know you and some other very good shooters trust your 100 yard development. But for me I have seen this happen before. I have shot the same loads at 100 and 1000. My upper node which gave me 1 3/4'' of vertical at 1k gave me a .350 vertical group at 100, same speed over the chrony. The reason I have been pulling my hair out on this barrel is I have been testing at 100 because the conditions have been so bad, the load that shoots in the .1s at 100 is the load that shoot 7'' at 1k, and both the loads shoot 10 fps ES or better. I think this is an odd barrel, but had I just went to 1k to test as usual I'd have my load by now.

 

[Erik Cortina]

Seating depth will

Load powder charge to where it's stable, them adjust seating depth. If still not happy with results after adjusting seating depth, get a barrel tuner to bring the groups in the rest of the way.

Erik,
Once the powder charge is determined, can any generalization be made as to what to expect optimizing seating depth to do to the shape of a group? Obviously it should minimize group size, but does it tend to have a greater effect on vertical, horizontal, or an equal effect on both? Or does the effect of optimizing seating depth on group shape tend to be highly rifle/load specific?

It will affect both vertical and horizontal, thus making groups smaller.

I usually adjust seating depth and can see the groups tightening before getting bigger again. I then select the seating depth where the groups were the smallest and tune using barrel tuner after that. Tuner will usually take those groups and shrink them even more, unless the barrel harmonics and load already match perfectly.

 

[amlevin]

I usually adjust seating depth and can see the groups tightening before getting bigger again. I then select the seating depth where the groups were the smallest and tune using barrel tuner after that. Tuner will usually take those groups and shrink them even more, unless the barrel harmonics and load already match perfectly.

I didn't add a barrel tuner, I added a muzzle brake. It shrunk my previously developed groups drastically.

Didn't make my fellow shooters all that happy though

BTW, I saw a shooter at the range the other day that uses "Shaft Collar's" as barrel tuners. Collars that are designed to keep shafts centered on bearings, etc, right out of the hardware store. Moves it back and forth a few fractions to "tune". Doesn't look all that sexy but it sure worked on his rifle.

 

[BradY]

Erik- I spoke to Steve recently via pm about it, but have you ever found your powder charge and set a bullet how far you wanted it, then dialled in the tuner to suit the group shape? Is it possible to do this? Some shooters here have said they do their velocity testing to get best ES then use tuners straight up to get their group size working. It seems to work quite well.

I have seen some rifles (and I think my current 7mm is in this bracket too) that can shoot ok at 300yds but dont really "hum" until they get to around 600yds and further back. No idea on ES at the moment- its actually having a tuner fitted this afternoon and I will get to do some 100yd testing tomorrow afternoon again for powder charge and 180 hybrids before re installing the tuner and working on groups.

 

[Erik Cortina]

You can tune any load. I like to run through the entire series to make sure I don't leave any accuracy on the table.

I look for a stable powder load with low ES, then adjust seating depth, and finally adjust tuner.

 

[mikecr]

I look for a stable powder load with low ES, then adjust seating depth, and finally adjust tuner.

See to me, adjusting a tuner is like adjusting charge (accuracy-wise, not ES-wise).
And so when you don't have a tuner, adjusting seating depth 1st, followed by powder is similar to your method here. The only difference is that often ES ends up an abstract here.

I had the ultimate tuner once (Browing Boss), and did work well for me.