How calculate Time in Barrell

[harry_x1]

Hi,

I am trying to use the theory of Optimum Barrell Time. I found a chart which tells me different nodes for a 33 inch barrell.

However how do I calculate time inside barrell? I am shooting 300 grain bergers at 3150 fps. Is there a formula that can be reliably used for same?


thanks
Harjeet

 

[GLShooter]

Quickload will do that for you.

 

[CharlieNC]

I developed a simple calculation which provides a good estimate:

a. TheoBT (ms) = Barrel Length(in)/12/Velocity(fps)/1000

b. QL BT = 0.114 + 1.77 Theo BT - 0.00916 Barrel Length

This correlates well with the Quickload (QL) calculations across a range of cartridges which were evaluated.

 

[jelenko]

Gordons Reloading Tool will also provide barrel time and optimum barrel time.
It's free!

 

[SeabeeKen]

Here is Chris Longs chart and website. He came up with it. You just need to know speed and barrel length

Optimal Barrel Time Concept

 

[Webster]

Hi,

I am trying to use the theory of Optimum Barrell Time. I found a chart which tells me different nodes for a 33 inch barrell.

However how do I calculate time inside barrell? I am shooting 300 grain bergers at 3150 fps. Is there a formula that can be reliably used for same?


thanks
Harjeet

Would the vibration pattern vary with barrel taper. A fluted barrel? No matter what you come up with you have to shoot the gun to varify. Different powders may give a different acceleration rates to the bullet with the same barrell time and muzzle velocity?

 

[gunsandgunsmithing]

I'm just not a believer at all. There are simply sooo many variables. Powder type, cartridge, lot to lot variations, temp, bbl stiffness.....air density. And frankly, I'm not sure any one of those except temp has anything to do with bbl length growth. I will just say this, because I believe it...If you run a tuner AND OBT.,.., AND you believe obt gets you close to a sweet spot(no, not a node) to the point of moving the tuner in tiny increments...then I'm all for it.
I think I understand the concept and have tested it many times but I've never...not once, come to my best tune with it. That's actually against the odds, too, because tune repeats and statistically speaking, I would've landed on a sweet spot a few times by now. The good news is that, I've never been more than 4-5 marks away on a centerfire and my tuner with OBT. The bad news news is, I've never been more than 4-5 marks away without OBT either. TIFWIF

 

[jelenko]

Would the vibration pattern vary with barrel taper. A fluted barrel? No matter what you come up with you have to shoot the gun to varify. Different powders may give a different acceleration rates to the bullet with the same barrell time and muzzle velocity?

Chris' theory was based solely on the speed of sound in the barrel => profile of the barrel wouldn't matter.

 

[SeabeeKen]

Gordons Reloading Tool will also provide barrel time and optimum barrel time.
It's free!

I had talked to Gordon about this before his passing. His testing showed that it was 40% accurate. My personal experience has been somewhat better. I always find a node, usually within .5 gr +/- of the GRT calculation

 

[gunsandgunsmithing]

I had talked to Gordon about this before his passing. His testing showed that it was 40% accurate. My personal experience has been somewhat better. I always find a node, usually within .5 gr +/- of the GRT calculation

That was my point. I believe at best, it can get you close. FWIW, .5-.6gr is frequently equal to only 2 marks away on my tuner. The other side of that coin is that it's only 4-5 marks between completely in tune, to completely out of tune.

 

[SteveOak]

Gordons Reloading Tool will also provide barrel time and optimum barrel time.
It's free!

You've got to like GRT.

 

[jelenko]

I had talked to Gordon about this before his passing. His testing showed that it was 40% accurate. My personal experience has been somewhat better. I always find a node, usually within .5 gr +/- of the GRT calculation

I saw the same from the fellow who did some training videos. For 223, I've also found a node that's usually within +/- .2 but not always. I've always found a node within +/- .5.

 

[CharlieNC]

When doing a ladder test to find the charge weight which yields a flat poi, this aligns well with OBT. The harmonic cycle of the poi does reflect the speed of sound but due to muzzle vibration, not muzzle diameter as proposed by Long.

 

[JEFFPPC]

Lots of theroy but the only thing that counts are the targets.

 

[harry_x1]

Last year I did use Quickload and found that the OBT does have some truth to it. Atleast in the 4 diff barrels I tested, I always found a node very close to the OBT prediction. Unfortunately this year, I moved 100% to mac ecosystem and cannot use quickload anymore, hence this question. Trying to waste as little bullet/powder as I can.

 

[Fern]

I might have to try and figure out grt. I plan on going to range to break in new barrel and would be nice not to burn through 8208 trying to find load.
Shooting a 204R with 11 twist 24” barrel. Going to be shooting 40gvmax and Winchester brass with 205m primers
Don’t suppose any savvy grt want to help me out

 

[Henryrifle]

Last year I did use Quickload and found that the OBT does have some truth to it. Atleast in the 4 diff barrels I tested, I always found a node very close to the OBT prediction. Unfortunately this year, I moved 100% to mac ecosystem and cannot use quickload anymore, hence this question. Trying to waste as little bullet/powder as I can.

Parallels or Fusion is the solution to running windows on the Mac painlessly.

 

[chop house]

I saw the same from the fellow who did some training videos. For 223, I've also found a node that's usually within +/- .2 but not always. I've always found a node within +/- .5.

first, i use grt and really like it. now, to be fair, here is grt obt estimation on 6 bra with varget in 26" bbl and 75 grn bullet (it's what info just happens to be in front of me)

#4 31.3 grns at 3106 (~45k psi)
#3 32.8 grns at 3248 (~52k psi)

to save all the math, that is about 4.5% apart with the charge weight delta of 1.5 grains, or +/- 0.75.

scale that down to .223 (and those charge wts), seems you can not help but be within ~+/- 0.5 ?

 

[jelenko]

scale that down to .223 (and those charge wts), seems you can not help but be within ~+/- 0.5

Exactly.
And, to your point, for 223 we could randomly pick a 1 grain charge range and find a node in 223 without using GRT at all.
I like to start with GRT to see where a node should be, avoid straying in to high pressures and to, if possible, avoid the half nodes.

 

[jxb]

Last year I did use Quickload and found that the OBT does have some truth to it. Atleast in the 4 diff barrels I tested, I always found a node very close to the OBT prediction. Unfortunately this year, I moved 100% to mac ecosystem and cannot use quickload anymore, hence this question. Trying to waste as little bullet/powder as I can.

Just spin up a vm on your mac with the same OS you're used to running QL then install QL on it. When you want to run QL, spin up the VM and there ya go. No need to make life difficult if you're used to QL there ya go. macos can also emulate but it may be easier to use a vm. I like virtualbox but there's lots out there and likely better ones for use on a mac.