Is Node Spacing Predictable?

[rckendall]

Since I don't have a Windows computer, I don't have Quick Loads and what I have learned about node study has been second hand through this forum. My current situation is that I found a really nice node, but it is just a bit too hot. I get intermittent issues with hard to open the bolt. I would like to find the next lower node. Is it predictable enough that it would be found at 1.0 to 1.5 (or) grain down?

The particulars for the rifle are: 308, 175 gn SMK over 42.9 gn Varget, 30" Bartlein barrel with 1/10 twist. I know that I must do further testing but it would be helpful to know which area to explore.

Thanks,
Richard

 

[jrb572]

Are you getting hard bolt lift or cratered primers?

 

[rckendall]

I'm getting hard bolt lift only and that is just at the very top. I'm thinking that is when the case gets pulled free from the chamber.

 

[Ned Ludd]

Unless the rifle has extremely short freebore or your lot of Varget is very fast, 42.9 gr of Varget with a 175 SMK shouldn't even be close to MAX pressure. Hard bolt lift near top of the upstroke can sometimes indicate you're not sizing down the base of the case sufficiently. It may be that a small-base die would solve your bolt lift issues. Are you observing any other pressure signs such as flattened/cratered primers, ejector marks, etc.? Although they may not always be 100% reliable indicators, I wouldn't be surprised if you noticed some/all of these of your load is really "hot". What are the load specifics (i.e. COAL, type of brass, velocity, etc.)? It really doesn't sound as though you should be having pressure issues with that load, unless it's caused by some other load/rifle-specific parameter that you didn't mention.

FWIW - I run Quickload on a Mac with no problem. You simply need some type of PC emulation software. I use "Crossover", but there are plenty of others, some of which are freeware. Quickload can be a very useful tool and the lack of a Windows-based computer isn't necessarily a deal-breaker for running QL.

 

[rckendall]

Unless the rifle has extremely short freebore or your lot of Varget is very fast, 42.9 gr of Varget with a 175 SMK shouldn't even be close to MAX pressure. Hard bolt lift near top of the upstroke can sometimes indicate you're not sizing down the base of the case sufficiently. It may be that a small-base die would solve your bolt lift issues. Are you observing any other pressure signs such as flattened/cratered primers, ejector marks, etc.? Although they may not always be 100% reliable indicators, I wouldn't be surprised if you noticed some/all of these of your load is really "hot". What are the load specifics (i.e. COAL, type of brass, velocity, etc.)? It really doesn't sound as though you should be having pressure issues with that load, unless it's caused by some other load/rifle-specific parameter that you didn't mention.

FWIW - I run Quickload on a Mac with no problem. You simply need some type of PC emulation software. I use "Crossover", but there are plenty of others, some of which are freeware. Quickload can be a very useful tool and the lack of a Windows-based computer isn't necessarily a deal-breaker for running QL.

Thanks for your very helpful reply! I am, and always do get flattened primers (Fed 210M) but no cratering or ejector markings. Also, how flat is flat? My gunsmith told me to look for some radius left at the edges of the primer, which is there somewhat.

The brass is LC Match that I have had for years and years and I believe it to be once fired only. They fit nicely in a Wilson chamber gage and they chamber in the rifle properly. The CBTO dim is 2.267 and the COAL is 2.834.

I have previously shot this rifle with Lapua brass and Berger Juggernauts with more powder, and the two types of brass measure pretty close in volume, by my measurements. So I wasn't expecting any pressure issues, but I did encounter the stiff bolt lift in today's testing session.

Thanks also for the tip on the software that would allow me to use QL. I will definitely look into that.

Thanks again,
Richard

 

[dcali]

That doesn't sound hot at all. max should be closer to 45 grains. Are you full length sizing?

 

[Mikemci]

Try 3% lower. Seems to get me very close.

 

[eric32]

that bolt click at the top of the lift is the case web getting stuck in your chamber.

check your brass after sizing and see if they are larger than .470 to .4715 depending on your chamber

i am speaking from experience of this matter

 

[jsthntn247]

Have you shot this brass in a different gun? Only take one shot in a fatter chamber. Nodes are normally 3% apart.

 

[1lnbrdg]

If you don't have a small-base die, a quick dirty trial involves a .45ACP die. Take the guts out of the die and size the brass thru it (same as a small-base die) then go fire it. If you are still having problems, it's not the sizing.

This is nothing new from once-fired GI brass.

 

[rckendall]

that bolt click at the top of the lift is the case web getting stuck in your chamber.

check your brass after sizing and see if they are larger than .470 to .4715 depending on your chamber

i am speaking from experience of this matter

My prepp'ed brass measures .469 at the base. My fired cases measure .469 at the base too. They fit in a Wilson chamber gage and chamber fine.

Also, thanks to those who gave 3% as the node spacing.

Thanks to all,
Richard

Edit to add: I called Sierra and was told that I was 1.2 gn over their recommended max load. Although my cartridges are .034 longer, I think that I really am a little hot. I'll load a few and test in the 3% lower range and report the results.

 

[eric32]

are you measuring at the .200 webline?

 

[dcali]

Sierra is really conservative relative to others. Their max load is under Hodgdon's starting load. I have no idea why there is such a huge discrepancy. I know, different barrels, brass, etc etc, but that's a huge difference.

 

[1lnbrdg]

Just a memory that is over half-a-century old but saw printed somewhere that nodes run about 1.5% of powder weight for a given cartridge and this has been pretty close when I was testing.

 

[jsthntn247]

Just a memory that is over half-a-century old but saw printed somewhere that nodes run about 1.5% of powder weight for a given cartridge and this has been pretty close when I was testing.

This is true but you have a accuracy node followed by a scatter node 1.5% higher followed by another accuracy node 1.5% higher. So there are 3% difference between each type of node.

 

[dcali]

There is no constant percentage that will find the "node" spacing. It depends on the rifle. For example, I did some load development where the peaks in group size were roughly 0.4 - 0.5 grains apart (out of 44), or about 1%.

http://bisonballistics.com/articles/sort-of-scientific-load-development-for-f-class

 

[JASmith]

My prepp'ed brass measures .469 at the base. My fired cases measure .469 at the base too. They fit in a Wilson chamber gage and chamber fine...

The lack of base diameter change suggests the pressures are reasonable for the .308 Win. The underlying question is the amount of cold work put into the bases during previous firings. We would need to measure unfired cases to see how much base diameter change has happened from unfired to current shot.

See http://shootersnotes.com/articles/when-are-pressures-too-high/ to get a more detailed explanation.

 

[Nature Boy]

The lack of base diameter change suggests the pressures are reasonable for the .308 Win. The underlying question is the amount of cold work put into the bases during previous firings. We would need to measure unfired cases to see how much base diameter change has happened from unfired to current shot.

See http://shootersnotes.com/articles/when-are-pressures-too-high/ to get a more detailed explanation.

Where exactly on the case are you measuring that?

 

[eric32]

.200 inches up from the casehead, is where you need to measure from. i think he just need a small base die to bring it back to spec