Getting higher velocity than predicted by QL

[uncle-buck]

Am a new QuickLoad user and also use a LabRadar.

Developed a new .308 Win. hunting load with Sierra's 180 gr. SBT bullet and found that LabRadar measured a MV that's 119 fps faster than predicted by QL after inputting bullet data, COAL, barrel length, case capacity, powder type and charge weight.

Am not complaining by any means, but am curious about the reason(s) and what input variables would need to be adjusted to get the software to predict actual results.

BTW, the ES on the last 5-shot string after getting the rifle zeroed yesterday was 11 and SD was 4.6, using a RCBS Chargemaster.

 

[BCBRAD]

Did you reconcile the start pressure?

 

[Bart B.]

Biggest contribution to the difference may be the powder lot. Each lot of a given powder is a little different from others.

Some may be small differences between other components and your barrel data compared to what QL got and calculated.

QL calculations shouldn't be expected to match exactly what your stuff does.

 

[uncle-buck]

Did you reconcile the start pressure?

No. How do you do that?

 

[BCBRAD]

If everything is inputted correctly the burn rate (Ba) is the final adjustment to be made.
The tune to velocity and OBT is made with powder charge.
Done properly it all works.
QL is there to do the math .

 

[BCBRAD]

The default is 3626 psi.
A cup&core bullet touching the lands is 3626+7200= 10,826psi.
for every 0.005" off the lands subtract 146psi.

So, if you are 0.030" off the lands the start pressure will be
10,826 psi - 730 psi = 10,096 psi

 

[CharlieNC]

The default is 3626 psi.
A cup&core bullet touching the lands is 3626+7200= 10,826psi.
for every 0.005" off the lands subtract 146psi.

So, if you are 0.030" off the lands the start pressure will be
10,826 psi - 730 psi = 10,096 psi

Interesting, do you have a reference which discusses the details?

 

[Bart B.]

Done properly it all works.

Are there different barrel metal inputs for stainless and chrome moly? There's about 3000 fps difference in shock wave speed between those metals.

 

[Uncle Ed]

The first thing you do with Quickload is enter the correct case capacity of a fired case from your rifle. Quickload defaults to the lowest case capacity and as a example with .223/5.56 cases it can cause a 5,000 psi difference in chamber pressure.

The second thing you do "IF" you have a chronograph is change the burn rate in Quickload until the velocity matches the chronograph.

After doing the above the Quickload chamber pressure "estimates" will be closer to actual chamber pressure.

There are simply too many variables in reloading components and firearms for accurate Quickload readings unless it is tweaked and adjusted.

 

[BCBRAD]

Interesting, do you have a reference which discusses the details?

Read the instruction manual for QL, also, look at the drop down in the shot start box.

 

[BCBRAD]

Are there different barrel metal inputs for stainless and chrome moly? There's about 3000 fps difference in shock wave speed between those metals.

What I have been working on is the shock wave or 'ring' (radial and from breech to muzzle) is 18,000 to 19,000 ft/s for chrome moly and s/s.

 

[Richard Coody]

like most computer programs you can get whatever you want to out of it.

actually your barrel will tell you what it likes without any electronics.

 

[68cuda340]

I'd stock up on that powder and primer lot and then have a nice single malt to celebrate a win!

 

[BCBRAD]

The first thing you do with Quickload is enter the correct case capacity of a fired case from your rifle. Quickload defaults to the lowest case capacity and as a example with .223/5.56 cases it can cause a 5,000 psi difference in chamber pressure.

The second thing you do "IF" you have a chronograph is change the burn rate in Quickload until the velocity matches the chronograph.

After doing the above the Quickload chamber pressure "estimates" will be closer to actual chamber pressure.

There are simply too many variables in reloading components and firearms for accurate Quickload readings unless it is tweaked and adjusted.

All other inputs must be accurate, adjusting Ba is the last thing to do, if necessary.

What I do is load 5 rounds then record velocity with a LabRadar. If the velocity is off then adjust Ba, then adjust powder charge to get predicted velocity and OBT.

 

[BCBRAD]

like most computer programs you can get whatever you want to out of it.

actually your barrel will tell you what it likes without any electronics.

Electronics makes short work of it, the paper result will be the same.

 

[BCBRAD]

With out accurate velocities QL is a non-starter.

 

[Richard Coody]

it will certainly be a sad day for me when all you have to do to get the most accuracy out of your rifle is plug a bunch of information into a computer. I love the challenge of load development. After i have gotten the best out of a rifle i seem to lose interest in it and move on to the next.

now i am old. they had dial temephones when i was a kid. my high school didn't have a computer. i hate to go somewhere and look around the room and you don't see anyone talking. they are all texting their other friends

i am just not so sure those olden days weren't the best.ones.

 

[Murray Brook]

Not sure if it was mentioned, but don't forget to adjust the weight factor for the cartridge used. For the 308 Win it is 0.53 You do this before adjusting the burn rate of the powder.

 

[BCBRAD]

it will certainly be a sad day for me when all you have to do to get the most accuracy out of your rifle is plug a bunch of information into a computer. I love the challenge of load development. After i have gotten the best out of a rifle i seem to lose interest in it and move on to the next.

now i am old. they had dial temephones when i was a kid. my high school didn't have a computer. i hate to go somewhere and look around the room and you don't see anyone talking. they are all texting their other friends

i am just not so sure those olden days weren't the best.ones.

I was ~12 years old when my folks got a dial phone.

 

[savagedasher]

Isn’t that the reason all loading books says start low and work up
The reason is the don’t know the case capacity the actual burn rate
of powder and the temperature
My QL is almost dead on with my. Powder
But Varget depending on the lot can very 80 fps