Quickload question
- Thread starter cj8vet
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Ned Ludd
Silver $$ Contributor
A brake is ported, therefore pressure behind the bullet is vented as the bullet passes. Also, it's not rifled inside. There are numerous reasons why it would not be considered part of the barrel length. Further, I believe you're referring to OBT Nodes, not QuickLoad Nodes. QuickLoad is merely a tool that predicts barrel occupancy times, not "nodes" that are associated with precision/accuracy. Optimized Barrel Time is the theory associated with accuracy nodes and barrel times. If you read the linked article about OBT, you might begin to understand Damon's comment above a little better. Sometimes it's better to try something without asking too many questions and see if it works at all first, before trying to get down into the weeds about how it works.
Chances are good that you will find a few more things that puzzle you as you read the article. For example, (somewhat analogous to your initial question) why isn't the action itself considered in the length? I guarantee that any longitudinal shockwaves don't know where the barrel steel ends and the action steel begins. Nonetheless, people have used this method successfully, even if the explanation for exactly how it works may leave something to be desired.
http://www.the-long-family.com/OBT_paper.htm
Chances are good that you will find a few more things that puzzle you as you read the article. For example, (somewhat analogous to your initial question) why isn't the action itself considered in the length? I guarantee that any longitudinal shockwaves don't know where the barrel steel ends and the action steel begins. Nonetheless, people have used this method successfully, even if the explanation for exactly how it works may leave something to be desired.
http://www.the-long-family.com/OBT_paper.htm
Brakes do not contact the bullet, the inside diameter of the brake is .005" to .040" over the size of the bullet (depending on what the manufacturer thinks is most accurate and safe). Once the bullet no longer contacts the bore the barrel vibrations will not effect it's performance.
As Ned said, QuickLoad simply provides you with the time that the bullet is in the barrel (barrel time) and you can use that information to help tune the load so that the bullet leaves the muzzle around an OBT node.
As Ned said, QuickLoad simply provides you with the time that the bullet is in the barrel (barrel time) and you can use that information to help tune the load so that the bullet leaves the muzzle around an OBT node.
It is only an approximation. Your components and barrel are different than what Quickload used to get data.
I assume that most people understand that any simulation software will only provide us with approximations, that seems obvious to me. But since the software's approximation is repeatable we can use it as a marker to make adjustments from. It's not perfectly accurate but it's better than a SWAG (scientific, wild-assed guess).
dcali
Bullet Maker
This is the important part. QucikLOAD gives a pretty good indication of barrel time and velocity given good inputs. What you do with that is up to you. The OBT nodes are another matter. I personally don’t believe in them and could spend a long time explaining why. Others say what amounts to “I don’t know why, but they seem to work”. I think part of the disagreement is the definition of “works”. Either way, mileage may vary.
The bigger picture is that barrel time is significant factor in a good load. Where QuickLOAD shines in in selecting a powder in the first place, and in replicating (very nearly at least) a good load with a different powder. It’s also quite good at estimating pressure changes due to unusual seating deapths (such as the crazy long .308 bullets that FTR shooters use). I’m much less enthusiastic about using it to find an accurate load. For that you need to test.
What about the fact that the same load and rifle system won't produce the same muzzle velocity across several people shooting it?
We all don't hold the rifle the same way during barrel time.
To say nothing about several barrels the same length won't shoot the same load to equal velocity. A 30 caliber barrel with a .3065" groove won't shoot the same load at the same speed as a .3087" one. 30 caliber bullet diameters I've mic'd are .3070" to .3092". Quickload doesn't allow those inputs.
Twist rate and bore diameter changes the numbers
I work up loads with QL and the OBT is usually not reliable, but half the time is close enough to give you an idea where to dig around. But otherwise I have to true the inputs for Shot Start pressure, Burn Rate Factor Ba, bullet length, case capacity.
One time the OBT predicted by QL was true (100% on the money), but that's because I knew the barrel well enough to know how to adjust the shot start pressure when in the lands (but not jammed). It ended up being the most accurate load I've ever shot in that barrel.
One time the OBT predicted by QL was true (100% on the money), but that's because I knew the barrel well enough to know how to adjust the shot start pressure when in the lands (but not jammed). It ended up being the most accurate load I've ever shot in that barrel.
How can that be when several velocity changing parameters can not be input to the software?
Every velocity affecting parameter can be changed in QL, including bullet diameter/weight, barrel groove diameter and cross-sectional bore area & barrel length, case weighting factor, starting pressure, capacity manual entry & adjusted for bullet area seated. Then there are the powder parameters, temperature and friction adjustments.
What version of QL estimates OBT?
My versions don't.
To the original question about barrel length and OBT:
This is about a percussion wave beginning from peak pressure point (assumed middle of chamber) to muzzle, reflecting back to breech, reflecting back to muzzle, over & over, speed of sound in metal. The traveling wave peak at any given point changes the bore/groove dimensions, and you should not want to put your bullet exit in coincidence with a muzzle that is compromised with this.
The threading of a break, and the action, disrupts efficient continuation of the percussion wave, so most is simply reflecting back & forth within muzzle/breech. Also, neither break nor action dimensional changes, if occurring, mean anything to bullet release.
It's interesting, but there are vastly more important nodes manifesting with load development.
What version of QL estimates OBT?
My versions don't.
To the original question about barrel length and OBT:
This is about a percussion wave beginning from peak pressure point (assumed middle of chamber) to muzzle, reflecting back to breech, reflecting back to muzzle, over & over, speed of sound in metal. The traveling wave peak at any given point changes the bore/groove dimensions, and you should not want to put your bullet exit in coincidence with a muzzle that is compromised with this.
The threading of a break, and the action, disrupts efficient continuation of the percussion wave, so most is simply reflecting back & forth within muzzle/breech. Also, neither break nor action dimensional changes, if occurring, mean anything to bullet release.
It's interesting, but there are vastly more important nodes manifesting with load development.
I have used QL for a few years now with very good success over a wide range of calibers, bullets and powders for myself as well as for many others. It takes a while to learn what adjustments and information it takes to get good output information.
There is truth in the old saying garbage in garbage out.
Well then, things have changed from when I first used it.
What powder parameters can be entered for the normal spread in a given powder lot's burn rate?
What's the bullet diameter spread for 30 caliber ones?
The simple truth is you need your actual case capacity from a case fired in your rifle. Quickload defaults to cases of the lowest capacity if you do not change it to the correct volume. With the .223 this can mean 6,000 psi difference between a case with 28.0 (default) and 30.6 case capacity.
Then you need a chronograph and change the burn rate rate in Quickload until the two velocities match. There are other tweaks but these are the main two adjustments. So do not buy Quickload if you do not have a chronograph and want accurate chamber pressure estimates.
After tweaking Quickload your velocity and pressure estimates will be close to actual. Then if you have OCD you can buy a Pressure Trace system and start publishing your own reloading manuals.
Then you need a chronograph and change the burn rate rate in Quickload until the two velocities match. There are other tweaks but these are the main two adjustments. So do not buy Quickload if you do not have a chronograph and want accurate chamber pressure estimates.
After tweaking Quickload your velocity and pressure estimates will be close to actual. Then if you have OCD you can buy a Pressure Trace system and start publishing your own reloading manuals.
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Zero, Have back-tested my best loads and found the barrel times to be in the range of 1-2% Longer Duration than Long’s original predictions FWIW
Ned Ludd
Silver $$ Contributor
Same here...for many different rifles/bullets/calibers, etc. No possible way is that a "coincidence". In my hands, optimal barrel times (according to calibrated QL values) almost always fall just a tick slower than reported in Chris Long's table, typically by 0.5 to 1.0%. My guess is that such a relatively small difference might be due to chronograph error, a slight differences in inputs such as true barrel length, case volume, or any one of half a dozen other very minor things. Frankly, I'm surprised the tOBT able values are as close as they are.
The inputs to QL all have an influence on velocity as does external temperatures.
Things get real when velocity recorded with a LabRadar, which has a 0.1% error, this is ~3 ft/s in a 3000 ft/s round.
Hot/cold primers effect velocity as do 'fast' barrels vs 'slow' barrels.
Pressure begets velocity.
An operator of QL will get better results if all weights and measures are done by the user as opposed to relying on the defaults as well.
Your loaded ammo must have a low ES to take full advantage of the math.
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