Accuracy nodes?

[Medium rare]

Do you think in a particular barrel the accuracy nodes are velocity or powder dependent? For instance my FTR rifle has a really good accuracy node around 2475fps with 215s and Varget. Would there also be the same node with a different powder at the same velocity?

 

[waldo1979]

Google "optimal barrel time".

 

[CharlieNC]

It will be close since velocity and barrel time are highly correlated. But not exactly because the pressure and velocity profile as the bullet progresses thru the barrel will differ between powders.

 

[Medium rare]

Thanks

 

[tn6br]

It will be close since velocity and barrel time are highly correlated. But not exactly because the pressure and velocity profile as the bullet progresses thru the barrel will differ between powders.

Thats where a barrel tuner would be handy.

 

[Brians356]

It will be close since velocity and barrel time are highly correlated. But not exactly because the pressure and velocity profile as the bullet progresses thru the barrel will differ between powders.

And different pressure profiles could (must?) induce different vibration profiles in the same barrel.
-

 

[gsg5pk]

Do you think in a particular barrel the accuracy nodes are velocity or powder dependent? For instance my FTR rifle has a really good accuracy node around 2475fps with 215s and Varget. Would there also be the same node with a different powder at the same velocity?

How many of varget you use to run those 215 at 2,475?

What barrel length?

 

[CharlieNC]

To answer this type question using Quick Load and Optimum Barrel Time together is your friend. The majority who use this approach are convinced it is valid, while many will not try it because they do not think it can work.

 

[Medium rare]

How many of varget you use to run those 215 at 2,475?

What barrel length?

Barrel is 31 and some change and powder node is between 40-41 Varget.

 

[Ned Ludd]

Do you think in a particular barrel the accuracy nodes are velocity or powder dependent? For instance my FTR rifle has a really good accuracy node around 2475fps with 215s and Varget. Would there also be the same node with a different powder at the same velocity?

Both. It's not just velocity, it's acceleration. At a given acceleration, velocity is strongly dependent on powder for a given charge weight and barrel length. The same approximate velocity can be achieved using a different powder with different acceleration, but the barrel harmonics may be quite different.

There *might* be if the burn rates for the two powder were very close. As noted above, similar velocity can sometimes be achieved with two different powders of significantly different burn rate due to the fact that acceleration in the barrel may also be quite different. If you use two different powders, but achieve the same approximate muzzle velocity by varying charge weight and differential acceleration, there is no guarantee that the barrel harmonics will be even close to the same, regardless of the fact that the bullets will ultimately be leaving the muzzle with approximately the same velocity. Quickload curves are a good illustration for this concept and QL can also be a very helpful tool to predict load behavior. However, sometimes the best/only way to really know for sure is to load some rounds and test them.

 

[gsg5pk]

Barrel is 31 and some change and powder node is between 40-41 Varget.

I'm currently working load up for this projectile too.

What is your chamber freebore and load round COAL?

 

[Medium rare]

I would recommend a 250ish freebore which keeps you off of the donut. Mine was throated out so I don't have a throat number for you but my bearing surface is just above neck shoulder junction.

 

[gsg5pk]

I would recommend a 250ish freebore which keeps you off of the donut. Mine was throated out so I don't have a throat number for you but my bearing surface is just above neck shoulder junction.

How about COAL of your load round?

 

[Steve Blair]

I didn't shoot 215 Hybrids in .308 but shot a lot of 230 Hybrids. My reamer has a .280" freebore for a COAL of 3.185" when jumping .018". Velocity in a 30" barrel was 2460 fps with 46.0 grains H4350 and was a precise load. That is a fairly heavily compressed charge but not high pressure. 215 Hybrids are ~.075" shorter than 230's and my .280" freebore was designed to allow up to .030" bullet jump without donut interference. It seems like something around .210-.220" freebore would be safe for 215's.

 

[Medium rare]

I would listen to steve. He has a ton more experience with the heavies than I do. I will measure my coal when I get home. I am at lapua regionals at bayou rifles shooting and I don't have my calipers.

 

[Steve Blair]

I would listen to steve. He has a ton more experience with the heavies than I do. I will measure my coal when I get home. I am at lapua regionals at bayou rifles shooting and I don't have my calipers.

I appreciate the kind remark but your estimate is also fine. Another shooter who competed 215 Hybrids used my .300 WSM reamer and had no problem making them work. A better answer is that anything from .210-.280" is likely to have no problems.

Good luck at Houston.

 

[Medium rare]

Thanks Steve. I ended up in 2nd with 980-33X. Ray Weaver kicked my high knee with a 983.

 

[Steve Blair]

An excellent result in an always tough crowd.

 

[Joe R]

Both. It's not just velocity, it's acceleration. At a given acceleration, velocity is strongly dependent on powder for a given charge weight and barrel length. The same approximate velocity can be achieved using a different powder with different acceleration, but the barrel harmonics may be quite different.

There *might* be if the burn rates for the two powder were very close. As noted above, similar velocity can sometimes be achieved with two different powders of significantly different burn rate due to the fact that acceleration in the barrel may also be quite different. If you use two different powders, but achieve the same approximate muzzle velocity by varying charge weight and differential acceleration, there is no guarantee that the barrel harmonics will be even close to the same, regardless of the fact that the bullets will ultimately be leaving the muzzle with approximately the same velocity. Quickload curves are a good illustration for this concept and QL can also be a very helpful tool to predict load behavior. However, sometimes the best/only way to really know for sure is to load some rounds and test them.

Peter,
gstaylor nailed it.
Yeah, PJ was on fire yesterday in a switching wind that gave lots of guys fits. Congrats again.

Joe

 

[Medium rare]

Peter,
gstaylor nailed it.
Yeah, PJ was on fire yesterday in a switching wind that gave lots of guys fits. Congrats again.

Joe

Thanks Joe! You are too nice.