Playing with the app the field 1st node- you change that value and the fist node it calculates is that value. EX if you changed it to 4 then the first calculated would be number 4 and last would be 14.
Quickload Optimal barrel timing calculator download
- Thread starter kaduflyer
- Start date
No problem using the QL for the barrel time but is it based on bullet travel or barrel length. It does work but you may end up with a node with a lower than you want.
There is a difference between barrel length and bullet travel. For example my .257 Roberts barrel is 26" but according QL the bullet travel is 24.196" once all the reload cartridge dimensions are entered. Thus, according to QL, "bullet travel, measured from the location of bullet base in chambered cartridge to muzzle." So, is the barrel time in ms per QL based on barrel length or bullet travel? Once that is known then we can use one or the other. I'm having hard finding any reference to this online.
There is a difference between barrel length and bullet travel. For example my .257 Roberts barrel is 26" but according QL the bullet travel is 24.196" once all the reload cartridge dimensions are entered. Thus, according to QL, "bullet travel, measured from the location of bullet base in chambered cartridge to muzzle." So, is the barrel time in ms per QL based on barrel length or bullet travel? Once that is known then we can use one or the other. I'm having hard finding any reference to this online.
A good internal ballistics simulator should be able to compute the bullet barrel travel time easily.
Known data:
COL
Bullet length
Add: BTOG
Add: Jump to the lands
IBS: would compute travel distance as
BTD = Barrel Length - (BTOG + JTL)
Note: a Muzzle device has an effect on MV but not bullet travel time
Known data:
COL
Bullet length
Add: BTOG
Add: Jump to the lands
IBS: would compute travel distance as
BTD = Barrel Length - (BTOG + JTL)
Note: a Muzzle device has an effect on MV but not bullet travel time
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Ned Ludd
Silver $$ Contributor
As I understand Chris Long's work, it is barrel length, not bullet travel. That is because his theory specifically opines that longitudinal shock waves travel through the length of the barrel, thereby negatively affecting precision when the location of the shockwave coincides with bullet exit from the muzzle. In other words, it's not the distance the bullet travels, it is the distance the shockwave travels back and forth through the barrel. However, there are plenty of skeptics regarding this particular explanation of the mechanism by which OBT Theory works, so that needs to be taken with a grain of salt. Many questions remain. For example, does this supposed shockwave simply stop where the barrel screws into the action, then head back the other way? Why would it not continue into the action itself? To be certain, I don't have the answers to any of these questions.
Nonetheless, in my hands certain OBT Nodes exist right where the OBT Table suggests they should be, and they appear to work very well (i.e. Node 4), matching up quite nicely to QuickLoad predictions for the specific barrel length, bullet weights, powder, and muzzle velocities I have obtained, using barrel length (rather than bullet travel length) as the input. Certain other loads I commonly use do not match up at all to predicted OBT Nodes, ending up perhaps halfway in-between predicted OBT Nodes. But they also shoot very well, so it's unclear to me whether the OBT "longitudinal shockwave" explanation is correct. Certainly some of the OBT Nodes are right where they're predicted to be, but that does the explanation of the mechanism which governs their location is correct, or constitutes the whole story.
jelenko
Gold $$ Contributor
Ned - I've read Chris' paper on OBT.
A node is where the travel time of the bullet matches the time the results of the shockwave is the least at the muzzle => there are two 'times' needed to calculate Optimum Barrel Time - one for travel time of the shockwave through the barrel and another one for the time the bullet spends in the barrel after it starts to move.
I've used GRT for over a year now. I've also found that there isn't always a node where one is predicted. I have found that about half the time the recommended powder charge is within a node. If not, it's almost always less than 0.3 grains on either side.
It's important to note that I'm looking for 1/2 to 3/4 MOA groups - so what is a node to me may be worthless to others.
Ned Ludd
Silver $$ Contributor
I think we're on the same page. What I was getting at is that the barrel occupancy times as calculated for the OBT Table are based on barrel length, not bullet travel length. Bullet travel length comes into play when programs such as QL or GRT are used estimate the barrel occupancy time when trying to hit an OBT Node. Even then, QL does not require the user to enter a bullet travel length; that is calculated by the program and is not write-enabled in the version of QL I have. I can't speak to how GRT does it as I don't use that software. I think the other factor that comes into play with QL is that the barrel occupancy time is estimated by default in the program from 10% Pmax to muzzle. I don't really understand why that particular parameter (10% Pmax to muzzle) was chosen as the default, but changing it to say 8%, or 12%, or some other value would certainly affect the barrel occupancy time output. As you noted, my Node 4 OBT loads with a 30" barrel are also very close to the predicted OBT values in the table, typically just a hair slower. For example, at Node 4 which is listed in the OBT Table as 1.3684 ms for a 30" barrel, my best loads usually come in ever so slightly slower at around 1.372-1.376 ms. I have always assumed that the reason(s) for that entail subtle variances/discrepancies in the measured load data inputs, actual muzzle velocity readings, and/or possibly the 10% Pmax value. Whatever the reason, the Node is very close to where the Table suggests it should be, if not exactly spot on the predicted barrel occupancy time in the Table.
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jelenko
Gold $$ Contributor
Got it.
FYI. I think the 10% Pmax is an estimate of when the bullet first starts to move out of the case.
If resonance starts at the chamber and travels to the muzzle (and back and forth several time), would it not also travel in the opposite direction back thru the steel of the receiver?
If the above is correct (I suspect so as I would think it physically impossible for resonance to initially travel only forward ??), then wouldn't you have a symphony of resonance going back and forth? Once the rearward travelling resonance reaches the stock, it surely travels back forward and meets the resonance that initially travelled forward and has returned?
.
If the above is correct (I suspect so as I would think it physically impossible for resonance to initially travel only forward ??), then wouldn't you have a symphony of resonance going back and forth? Once the rearward travelling resonance reaches the stock, it surely travels back forward and meets the resonance that initially travelled forward and has returned?
.
CharlieNC
Gold $$ Contributor
OBT is based on the longutinal speed of sound through steel which is the speed at which energy travels. Initially to the muzzle at which it reflects back to the receiver where it reverses again (thus multiple nodes), my guess is where the barrel joins the receiver. It is clear to me that OBT works not because the muzzle diameter varies but because there is an associated transverse vibration at the muzzle.
That was a great read. I actually printed it out for fear I’d never be able to find it again. Very interesting.
Dave
jelenko
Gold $$ Contributor
Absolutely. The motion of the muzzle [or any part of the barrel] is going to be the sum of all the waves moving back and forth. In fact, the shock wave travels many times back and forth in the barrel before the bullet arrives at the muzzle. Speed of sound in steel is ~ 17,000 fps => ~ 0.1ms. Bullets take ~ 1 ms to get through the barrel.
Chris Long developed a theory about accuracy nodes based on disturbance of the muzzle from the shockwave and the time it takes the bullet to reach the muzzle.
Likely yes, but the speed of sound in wood, carbon fiber or fiberglass is orders smaller than the speed of sound in steel (which is over 17 times faster than the speed of sound in air). But yes, you do have waves passing back and forth past one another.
Do they make a QL app for the iPhone? Or is QL only for the computer??
Dave
Dumb question, where does the barrel “start”? True length from end to end? From front of action to end of muzzle? How do you account for a barrel tuner attached to the end of the barrel?
Sorry…I need a QuickLoad for Dummies book…lol, and I’m not embarrassed to admit it.
Dave
There's no QL app for any phone. . . . so far.
A tuner only effects the harmonics, like the locations of the anti-node of the sine wave not the amount of time the bullet travels through thee barrel. With a tuner you're changing the harmonics and trying to match the position of an anti-node with the moment the bullet leaves the muzzle.
According to Long, The goal is to get the bullet to leave the muzzle at the point when the muzzle diameter is at smallest (ie no gas blow by).
I guess I should have clarified my question, I meant do you include the tuner in the overall length of the barrel??
It doesn't make sense that it would since the bullet is no longer in contact with anything (other than the escaping gasses and the air in front of it).
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