What distance to the lands are you using? (12BVSS)

[Oly1]

Hi

I recently bought a 12BVSS (2004) in 308Win and was wondering what distance / jump to the lands (or COAL for 175gn bullets) most folk are finding that this make / model tends to like?

Thanks in advance
Oly

[Ted_Feasel]

Hi

I recently bought a 12BVSS (2004) in 308Win and was wondering what distance / jump to the lands (or COAL for 175gn bullets) most folk are finding that this make / model tends to like?

Thanks in advance
OlyI started at 20 and found around .006 things got really tight, .004 sat pressure signs so left at .006.. start about 20 work closer in .005 increments.. that's what worked for me

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[CFJunkie]

I have 8 Savage rifles, two in .308, and every one has a different preference for jump length.

I would like to say that 0.020 is a good starting point, but a couple of my barrels are pretty far from that.

I'm afraid you are going to have to experiment with your particular barrel.

[Oly1]

Whilst not the easy answer I was hoping for (!) that's the info I wanted to know thanks.

I wasn't sure whether all being the same family they may "like" a set distance. But like all others, I'll just have to enjoy the refinement process!

Cheers
Oy

[Ted_Feasel]

Whilst not the easy answer I was hoping for (!) that's the info I wanted to know thanks.

I wasn't sure whether all being the same family they may "like" a set distance. But like all others, I'll just have to enjoy the refinement process!

Cheers
OyExactly lol.. that's really why I do it.. I hate.finding the load. I but a new rifle or build one when I do because I enjoy the journey:)

Btw, has anyone played with using "exit node" method to find their accuracy node? I've read what little I can find and admittedly I dont understand 100% of it but I get enough to understand the science behind it sounds solid. I was looking for more reading on it or details.. this sounds like something maybe Robin hood may know something about??

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[Oly1]

I have 8 Savage rifles, two in .308, and every one has a different preference for jump length.


Do you find that they all have similar throat lengths? What COAL are you using?

[charlie b]

I have the same rifle. I have not experimented with COAL and have kept to mfg recommended lengths. FWIW, the Sierra load data for the .308 uses a 12BVSS. That is good enough for sub MOA accuracy. I am sure if I did some more work with it I could get to 1/2MOA on a regular basis.

But.....I shoot mostly cast in mine and they are sized to be a friction fit in the throat/bore.

[std7mag]

For mine, it seems to more depend on bullet type.
Standard cup & core bullets (ELDX & ABLR included) seem to like about 0.020".
Berger VLD for mine like it up close & personal 0.005".
But others with the VLD found they like to jump (0.060"-0.090").

Monolithic bullets (Barnes, E-Tip, Cutting Edge) are recommended for a 0.050" jump.

[GaCop]

Exactly lol.. that's really why I do it.. I hate.finding the load. I but a new rifle or build one when I do because I enjoy the journey:)

Btw, has anyone played with using "exit node" method to find their accuracy node? I've read what little I can find and admittedly I dont understand 100% of it but I get enough to understand the science behind it sounds solid. I was looking for more reading on it or details.. this sounds like something maybe Robin hood may know something about??

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Haven't heard about "exit node". Something to look into.

[Ted_Feasel]

Haven't heard about "exit node". Something to look into.If you find any good articles about it I would love it if you put a link out to them and I will do the same it sounds very promising and a lot less painstaking

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[Nor Cal Mikie]

A .308 can use a longer freebore. The H.S. Precision uses a LOONG freebore and still produces bug holes. Most factory chambers are cut with a long freebore SO, you have to find out for yourself where the sweet spot is.
If you're going custom chamber, go short. Nothing worse than developing a bug hole load, and before you know it, everything changes because the throat wore and you can't get close to the lands and you end up starting all over from scratch.
Been there, had that happen and from that point on, nothing but custom cut chambers so I can get to the lands. I'am doing mostly small calibers so my freebore number is ZERO.
Gas gun?? That's another thing all together. The first slam fire or out of battery discharge from the lack of freebore will be a learning experience.:eek:

[Ted_Feasel]

I think someone sort of touched on this earlier in this thread but there are some bullets that are more jump sensitive than others. At least in my experience I have found that bergers are very jump sensitive where ELD match are not nearly as sensitive to jump space or so it seems and that's through my shilen and criterion barrels.
I've built many AR10 & 15s and have never had one fire out of battery. I have had slam fires using soft primers but switched to cci #41 and 34s and have not had a slam fire since. The most common cause for slam fires are putting a round in the chamber, ejecting and repeating many times. Each time the carrier slams into full battery, the firing pin lightly strikes the prime and repeated light strikes on the same primer eventually will close the gap on the anvil and cup and BOOM... 2and most common is not really a slam fire, it is a very light trigger pull with no/short reset/over travel.. that mainly happens on big bore ARs where the recoil can be strong enough it actually causes either the momentum to throw the trigger or the shooters finger to accidentally trip trigger:) just my 2 cent of 20 years building and repairing ARs

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[CFJunkie]

I'm not exactly sure what you mean by 'exit node'.

If you're referring to exit time tuning, then I can provide some information.

The bullet exit time is the time it takes for a bullet to proceed down the barrel and exit the rifling.
It is both powder charge and barrel length dependent because those two factors along with bullet weight determine how far and fast the bullet moves down the barrel.

When the round fires, there is a shock wave that tries to expand the barrel and it proceeds down the barrel towards the muzzle and then reflects back to the chamber. It does that again and again until the bullet exits.
The concept is that barrel steel has a reflection speed that is far faster than a bullet can progress down the barrel and leave the muzzle.
The reflection speed is dependent on barrel length too, but it is also dependent on the amount of carbon in the steel.
Old barrel steel, pre-WWII vintage barrel usually had a reflection speed of 18,916 fps.
Savage barrels use 3% carbon steel and have a reflection speed of 19,107 fps.
4140 and 4150 stainless have a speed of 19,969 fps.
416R stainless steel has a reflection speed of 20,014 fps.

To do anything with the theory, you need to know what your barrel length from breech to muzzle and the type of barrel steel.
It doesn't matter what caliber because the reflection travels in the steel not the hole in the barrel.

I find that for most calibers 6.5mm and larger, with barrel lengths of 24-inches, the bullet exits somewhere around 1.15 to 1.3 msec. depending upon what charge you use.

For a Savage 24 inch barrel, the reflection speed is about 0.104 msec. to go from chamber to muzzle.
It takes another 0.104 msec. to get back to the chamber. (the 2nd reflection).
That means that you have to set your load to get the 10th or 12th reflection, depending on how close you are getting to Pmax.
At the 12th reflection in a 24-inch Savage barrel, the exit time would be 1.256 msec.
If you set up your load to get your bullet to exit the muzzle at that exit time, that reflected shock wave is at the chamber and the vibrations at the muzzle are minimum and the crown is the tightest.
The theory is that it should yield the best accuracy.

A 26-inch Savage barrel has a 12th reflection time of 1.361 msec.
A 22 inch Savage barrel has a 12the reflection time of 1.154 msec.
It you use a muzzle brake, a flash hider or a suppressor you need to include that length because the reflection travels all the way to the end before it reflects.
The complication is that the steel in those devices has to be considered because it most likely isn't the same as the steel in the barrel.
Most of mine are 4150 steel. (Colt AR flash hiders also use 4150 steel)

I have tested this effect for about 3 years now and, after minimizing my shooter induced variations and taking temperature into consideration, I have found that my 7 most accurate rifles actually do shoot the best when I load for exit time and get it within 0.002 msec.
I have one rifle (maybe because the steel batch was slightly different or my barrel measurement was a bit off) that likes to be 0.005 faster than I calculated.
QuickLOAD gives you exit time for loads that seems to be accurate enough for my testing.
There is a difference of about 0.060 to 0.090 in average group accuracy between having the exit time with the reflection at the chamber or the reflection at the muzzle.

I have found that with a new rifle, and I have used the approach on three new rifles, I get great results right from the first groups.
Then all I have to do is find out what bullets, powders, bullet weights, and jump the rifle likes the best. They all seem to be different but I don't have to hunt for nodes.

[Ted_Feasel]

I'm not exactly sure what you mean by 'exit node'.

If you're referring to exit time tuning, then I can provide some information.

The bullet exit time is the time it takes for a bullet to proceed down the barrel and exit the rifling.
It is both powder charge and barrel length dependent because those two factors along with bullet weight determine how far and fast the bullet moves down the barrel.

When the round fires, there is a shock wave that tries to expand the barrel and it proceeds down the barrel towards the muzzle and then reflects back to the chamber. It does that again and again until the bullet exits.
The concept is that barrel steel has a reflection speed that is far faster than a bullet can progress down the barrel and leave the muzzle.
The reflection speed is dependent on barrel length too, but it is also dependent on the amount of carbon in the steel.
Old barrel steel, pre-WWII vintage barrel usually had a reflection speed of 18,916 fps.
Savage barrels use 3% carbon steel and have a reflection speed of 19,107 fps.
4140 and 4150 stainless have a speed of 19,969 fps.
416R stainless steel has a reflection speed of 20,014 fps.

To do anything with the theory, you need to know what your barrel length from breech to muzzle and the type of barrel steel.
It doesn't matter what caliber because the reflection travels in the steel not the hole in the barrel.

I find that for most calibers 6.5mm and larger, with barrel lengths of 24-inches, the bullet exits somewhere around 1.15 to 1.3 msec. depending upon what charge you use.

For a Savage 24 inch barrel, the reflection speed is about 0.104 msec. to go from chamber to muzzle.
It takes another 0.104 msec. to get back to the chamber. (the 2nd reflection).
That means that you have to set your load to get the 10th or 12th reflection, depending on how close you are getting to Pmax.
At the 12th reflection in a 24-inch Savage barrel, the exit time would be 1.256 msec.
If you set up your load to get your bullet to exit the muzzle at that exit time, that reflected shock wave is at the chamber and the vibrations at the muzzle are minimum and the crown is the tightest.
The theory is that it should yield the best accuracy.

A 26-inch Savage barrel has a 12th reflection time of 1.361 msec.
A 22 inch Savage barrel has a 12the reflection time of 1.154 msec.
It you use a muzzle brake, a flash hider or a suppressor you need to include that length because the reflection travels all the way to the end before it reflects.
The complication is that the steel in those devices has to be considered because it most likely isn't the same as the steel in the barrel.
Most of mine are 4150 steel. (Colt AR flash hiders also use 4150 steel)

I have tested this effect for about 3 years now and, after minimizing my shooter induced variations and taking temperature into consideration, I have found that my 7 most accurate rifles actually do shoot the best when I load for exit time and get it within 0.002 msec.
I have one rifle (maybe because the steel batch was slightly different or my barrel measurement was a bit off) that likes to be 0.005 faster than I calculated.
QuickLOAD gives you exit time for loads that seems to be accurate enough for my testing.
There is a difference of about 0.060 to 0.090 in average group accuracy between having the exit time with the reflection at the chamber or the reflection at the muzzle.

I have found that with a new rifle, and I have used the approach on three new rifles, I get great results right from the first groups.
Then all I have to do is find out what bullets, powders, bullet weights, and jump the rifle likes the best. They all seem to be different but I don't have to hunt for nodes.Yes[emoji4][emoji854]that is exactly what I'm asking about.. again I've found so little on it that I'm not sure about much but I did remember understanding to a degree the science behind it and thought it sounds promising.. the article I read about it (probably 2 months ago) said the theories and science on exactly how to do it is still being tested.. I will definitely read and reread your post on it.. thank you very much and if you happen to run across articles on practical application of it PLEASE post the link or PM me the link.. thanks again CFJunkie [emoji4]

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[CFJunkie]

In November 2014 I stumbled onto an old article by Christopher Long entitled “Shock Wave Theory – Rifle Internal Ballistics, Longitudinal Shock Waves, and Shot Dispersion”, written in 2004, that described the theory of how shock waves in a rifle barrel might change accuracy.
It might still be available if you Google it.

It seemed to be a reasonable idea but there were no documented results in the report that proved that the theory had merit, so I decided to try testing to determine if the theory might work.
I finally started to load ammo tuned for exit time early in 2015.
Consequently, when I started testing for exit time, I added bullet exit time to the data gathered for each load. Recently, I have also added the temperature recorded when the load was shot.

Initially, my results didn't seem to prove anything but I realized that the effects were being masked by my 'shooter induced variations'. I spent some time with my technique to reduce them and become more consistent and began to get valid data.
Once I realized that temperature sensitive powders were causing my expected velocity (that is related to exit time) to shift, I was able to adjust my expected data for temperature and found that there really was an effect.

I started with my .308s and my Les Baer Super Varmint .223.
When I got my 12 LRP 6.5mm Creedmoor, I used exit time exclusively to plan my loads and got incredible results without having to to shoot ladders.
I did shoot off the desired exit time to see what the magnitude of the effect was. It was measurable but not earthshaking - 0.060 to 0.090 on average depending upon the caliber.
My last two Savages, the 12 FV .223 and 12 FV 6.5mm Creedmoor have also shown great results using exit time.

I do remember seeing an article claiming to 'prove' Chris Long's theory, but I didn't think it had sufficient proof to support the claim. I may have a copy stored somewhere.

[mark r]

that's the reason we enjoy re-loading, we know our guns in a special way.

[CFJunkie]

Here is a link to the Long family's V4 report.
I don't think that is the original article, but it might help.

http://www.the-long-family.com/shock%20wave%20theory%20summary%20explanation.pdf

[Ted_Feasel]

In November 2014 I stumbled onto an old article by Christopher Long entitled “Shock Wave Theory – Rifle Internal Ballistics, Longitudinal Shock Waves, and Shot Dispersion”, written in 2004, that described the theory of how shock waves in a rifle barrel might change accuracy.
It might still be available if you Google it.

It seemed to be a reasonable idea but there were no documented results in the report that proved that the theory had merit, so I decided to try testing to determine if the theory might work.
I finally started to load ammo tuned for exit time early in 2015.
Consequently, when I started testing for exit time, I added bullet exit time to the data gathered for each load. Recently, I have also added the temperature recorded when the load was shot.

Initially, my results didn't seem to prove anything but I realized that the effects were being masked by my 'shooter induced variations'. I spent some time with my technique to reduce them and become more consistent and began to get valid data.
Once I realized that temperature sensitive powders were causing my expected velocity (that is related to exit time) to shift, I was able to adjust my expected data for temperature and found that there really was an effect.

I started with my .308s and my Les Baer Super Varmint .223.
When I got my 12 LRP 6.5mm Creedmoor, I used exit time exclusively to plan my loads and got incredible results without having to to shoot ladders.
I did shoot off the desired exit time to see what the magnitude of the effect was. It was measurable but not earthshaking - 0.060 to 0.090 on average depending upon the caliber.
My last two Savages, the 12 FV .223 and 12 FV 6.5mm Creedmoor have also shown great results using exit time.

I do remember seeing an article claiming to 'prove' Chris Long's theory, but I didn't think it had sufficient proof to support the claim. I may have a copy stored somewhere.I k know the article I first read said its still in the proving stage

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[Robinhood]

Until apps like quickload came along people found the node by shooting ammo loaded with each load having small increases of powder. The most accurate load was in the middle or near the middle of a group of loads that had the same POI or close to it. Obviously depending on distance.

[Ted_Feasel]

Until apps like quickload came along people found the node by shooting ammo loaded with each load having small increases of powder. The most accurate load was in the middle or near the middle of a group of loads that had the same POI or close to it. Obviously depending on distance.I just looked at quickload earlier, its $150... to much for me right now.. I'd definitely like to try it.. I'd be curious to see what it comes out with compared to what I've developed on a.few of my tac drivers

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