Wide node

[grovey]

From time to time I've seen posts where someone mentions a wide accuracy node. To me, it seems when I find the sweet spot ... a 1/10 of a gr either way wrecks the groups. What exactly defines a wide accuracy node ?

 

[Ledd Slinger]

I like to have at least 0.3 gr of forgiveness in either direction.

I have had some that will shoot the same POI and group with a full grain swing. LR drops change tho.

 

[Bart B.]

308 Win cartridges gave shot 168's through 300 yards with charge weights of IMR4064 over a 3 to 4 grain range into near half moa test group sizes. Each specified weight having a couple tenths grain spread in charge weights.

My guess is each weight made bullets leave the muzzle at the best angle to the line of fire to compensate for bullet drops for each muzzle velocity's spread in fps.

At longer ranges, one charge weight near maximum was best

 

[mike a]

So where's the list of cartridges that stay in tune the longest. Because that's what I want. How would a 6br compare to a 6.5x47. Say shooting just 1/2" groups at 100. I suppose the br would start out much smaller than 1/2 and go out of tune up to 1/2". Where as the 6.5 might start out at 1/2 and get bigger. Just thinkin Mike

 

[urbanrifleman]

Tune to the seating depth first and you will find that there is a seating depth that consistently shoots the smallest groups no matter the charge.

 

[urbanrifleman]

Note velocities around a true node (29.9) at optimum seating depth.

 

[mike a]

Tune to the seating depth first and you will find that there is a seating depth that consistently shoots the smallest groups no matter the charge.

Now you tell me. I did an ocw test and only one charge was fair. I did a seating test with that charge and got it dialed in. Played around with charge weight again and found them all good. Sure burned all of components.

 

[urbanrifleman]

Now you tell me. I did an ocw test and only one charge was fair. I did a seating test with that charge and got it dialed in. Played around with charge weight again and found them all good. Sure burned all of components.

The guy from Lapua that posts here says they recommend you do the seating test first with the minumum charge from the load book. Once you find the seating depth, you go up in charge.

 

[dsculley]

The larger the case, the wider the node in my experience. If you shoot groups and then pick the smallest group as your charge, many times it will fall out of tune if one small thing changes, eg. seating depth, actual charge weight, temp, etc.. If you run an OCW test or Ladder test then you can find nodes where consecutive charges shoot nearly the same vertical. That is a node. If you load to the middle of the node then small discrepancies in charge weight will not drastically change POI.

I agree with urbanrifleman, test for seating depth first with a safe charge. There is an ongoing debate on whether to test charge weight or seating depth. I have tried both and I get the best results by testing seating depth first (Berger test, coarse changes), then charge, then tweak seating depth (small changes).

 

[Ledd Slinger]

So where's the list of cartridges that stay in tune the longest. Because that's what I want....

I would say that has more to do with your barrel than the cartridge. The cases you listed will all tune well if you use a top quality action and barrel put together by a smith that knows how to do it properly. A bad barrel is a bad barrel no matter what you do. A good barrel with a poorly cut lands becomes a piece of junk.

Just about any custom barrel can shoot well, even the banana barrels. But I've heard straighter barrels will hold a tune better. I recently put a Broughton on a new build. The smith said it was one of the straightest bores he'd ever seen when indicating a barrel. Said it was nicer than any Krieger he's even installed. Hoping it will tune easy.

 

[Alex Wheeler]

You will find more variation in tune width from barrel to barrel than you will case to case. Most of the time a picky tune is because your not giving the barrel what it really wants. Maybe seating is off or its not loving the powder or primer. Some barrels are finicky, others are forgiving. The case volume plays a role in how many tenths of width. Also the accuracy your after. .5 moa= wide node .1moa=small node. Actions seem to play a huge role. A good action with good ignition seems to "find" really good barrels very often. While the same exact action make that is not as good struggles to "find" competitive barrels. Actions are SO much more important than most give them credit for.

 

[270WinDude]

The larger the case, the wider the node in my experience. If you shoot groups and then pick the smallest group as your charge, many times it will fall out of tune if one small thing changes, eg. seating depth, actual charge weight, temp, etc.. If you run an OCW test or Ladder test then you can find nodes where consecutive charges shoot nearly the same vertical. That is a node. If you load to the middle of the node then small discrepancies in charge weight will not drastically change POI.

I agree with urbanrifleman, test for seating depth first with a safe charge. There is an ongoing debate on whether to test charge weight or seating depth. I have tried both and I get the best results by testing seating depth first (Berger test, coarse changes), then charge, then tweak seating depth (small changes).

You're saying a ladder test would find a true node where as shooting for groups is something else? I recently did groups in .3gr increments I think. It seemed like I was looking at a ladder test in that there was 2 distinct tightening areas of the groups, usually for the 3-4 sets I tested it was at the lower end of charge and again at the higher.
I do worry seating depth can have adverse effect on testing. Perhaps if you can figure that out roughly in 12 rounds then I might start doing that first and then play around again after I find a sweetspot on a "node".

 

[Ledd Slinger]

Seems I find the most forgiving tunes at seating depths from a .005" jam, to .005" off the lands. You can play with seating depth a little more (maybe test from a .010" jam to .010" off) but somewhere in that 5 in to 5 off window is what always seems to work for me. I start with jamming the lands and work out.

 

[KenOath]

Seems I find the most forgiving tunes at seating depths from a .005" jam, to .005" off the lands. You can play with seating depth a little more (maybe test from a .010" jam to .010" off) but somewhere in that 5 in to 5 off window is what always seems to work for me. I start with jamming the lands and work out.

Are you talking 6BR and derivatives?

 

[Ledd Slinger]

Are you talking 6BR and derivatives?

No. Never owned a barrel chambered for anything derived off the 6BR case. I have multiple other 6mm cartridges it works for tho. Im talking about everything I use Berger or other high BC bullets in for long range. I imagine it would work well in a 6 BR too. Don't see why not. Perhaps those seating depths may not work as well with a lighter flat base bullet.

 

[Ledd Slinger]

Agreed. It also has a lot to do with bullet weight. Takes more energy to move larger mass.

In my last ladder test with a 338-375 Ruger, 0.2 gr increase in charge weight didn't even change the speed of the 250gr bullet. The next 0.2gr (0.4gr total increase) bumped the speed up about 10 fps. The next 0.2gr no speed change again. That 0.6gr increase is roughly only 3/4 of one percent change in total charge weight. So not really much change at all.

Bump a charge up 0.6gr on a 6BR with charge of 30gr and you've changed it by about 2%. Big difference, especially if running lighter bullets.

Now bump the 76.5gr charge weight of my 338-375 up 2%, which would be about 1.5gr, and I'll bet you there'd be a much bigger change in speed and possibly POI

 

[grovey]

Either of these will weigh to the individual kernel.

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We don't wear welding gloves when testing loads right? I think percentage wise we're looking at about the same thing. My lapua improved has a wider node in grains than my bra, but percentage of powder is about the same.

This is kind of where my mindset was when starting this thread. I can't help but think a better scale would show my charges are varying more than I know, and therefore my loads may be more forgiving than I think. The wide node has been elusive to me in cases up to .308 size. I'm only shooting/ competing with factory guns, but I'm trying to get the absolute most out of them.