Need explanation for higher than predicted velocity

[MarkG]

I'm playing around to get a feel for Quickload. I'm getting real good agreement for my 308 load, but my 25-06 data is way off.

IMR 4350 at 50grs with Hornady 110gr ELD-X - Barrel is 24":
Labradar: 3187 fps
Quickload: 2967 fps (Using 80 F propellant temp)
Hornady Manual: 2900 fps

I've raised the QL Ba by 15% and cut the bullet weight to 106gr and only got up to 3160 fps.
Any thoughts on how to explain this discrepancy?

 

[59FLH]

I came to this conclusion. QL works on a fudge factor of +/- 10% for powder lot variances. That has an effect on calculated velocity output.

I ran into the same issue and it caused me to question the accuracy of Labradar.

QL put my cartridge data @ 3000 fps,
LR measured it @ 3200 fps, the same 7% your experiencing.

 

[spclark]

Simulations using software are a poor substitute for results seen with the equipment you use in real life activity, that you then can repeat again at some other time.

They can get you close to what you might then expect, if that’s all you’re aiming for.

 

[FeMan]

That's QL in my experience. I have found it spot-on for some cartridges/loads and way off on others.

I start in QL with by making sure my case capacity and OAL are right, and my weighting factor is where I think it should be. I typically use it to find the velocity at which I will be at max pressure and then do a ladder over a chronogarph to find that charge weight. Although the powder charge often does not usually align with QL and is sometimes way off, I have found that the QL predicted velocity at max pressure and the field results correlate very closely. Trying to use QL to give me a powder charge to work with has been a failure for me.

 

[mikecr]

I've had excellent results with QL over the last 5 or 6 cartridges. There is something I see as a gotcha, many likely overlook. Review carefully that 'cross sectional bore area' that loads with specific cartridges. It was theirs and certainly may not match yours.
You can try other cartridges of same cal and enter/override your capacity to see if predictions align better than measured. Enter seated bullet shank depth, mind starting pressure, and weighting factor. Calibrate to your LabRadar.

 

[Capt. Oblivious]

The more you play with it you will see overbore cartridges like your 25-06 will sort of have a turbo effect when you get close to 55k psi preasure and the speed will go up more than youd think or more than what QL would predict. Drop your load a little to calibrate QL and then all you do is adjust the burn rate of your powder untill it lines up. I have done 1000s of QL “calculations” and you can get very close with QL

 

[MarkG]

Thank everyone for your replies. I adjusted the cartridge weighting factor to the recommended value for overbore cartridges, updated the cross sectional bore area using the calculate feature and measurements from my barrel and increased the Ba by 3.5%. I'm now predicting 3184 rather than 2967.

Earlier this week I loaded a 308 ladder around one of the Chris Long OBT nodes and the group, ES and SD all tightened up at the QL predicted charge wait.

Very pleased. Thanks,
Mark

 

[Ned Ludd]

As has been mentioned,variance in Lot-to-Lot powder burn rate (Ba) is one possibility. Ba for a given Lot of powder can also change with different cartridge shapes and volumes, different primers, and different bullets weights, all of which can affect pressure, and therefore also affect burn rate. Even using different primers can have an effect. Finally, you didn't mention the case volume you were using. Did you actually determine your average case volume by water weight? Or are you using the factory preset value? I have found the QuickLoad factory preset case volumes are off quite a bit for the cartridges and brands of brass I use.

 

[Zero333]

Case Capacity
Shot start pressure
Weighting factor
Burn Rate Factor BA

Quickload is not perfect and will have the odd huge discrepancy. At the same time I've had huge discrepancies from reloading manuals as well.

When I run RL-33 in Quickload with the 338 Lapua or 338 Norma, the results are not too far off.. but when I run RL-33 in the 300 winmag, Quickload shows 140 fps less velocity compared to my chrono.

When I started reloading I used the exact recipe from Hodgdon's data with the 243win and 105amax with H-4831. 2.760" COAL (0.040" Jump), Winchester brass and 210m primer. Hodgdon's data used 24" bbl and I had a 22".

Their max for this combo showed 41.0 gr and 2,846 fps.
My measured velocity at 41.0 gr was 2,603 fps !
Adjusting for my 2" shorter barrel, Hodgdon's data was roughly 200 fps faster.

Slowly I went up in charge weight over 2 more range trips and at 45.8 gr H-4831 I still didn't have any hints of pressure.
That's almost 5 gr over Hodgdon's MAX.. That's roughly 11 % more powder than Hodgdon's MAX and still no pressure signs !!!

 

[MarkG]

I did determine the water weight volume. Several of you have mentioned shot start pressure. What would I used as a basis to adjust this parameter?

 

[mikecr]

Several of you have mentioned shot start pressure. What would I used as a basis to adjust this parameter?

Your chronograph. Everything is ultimately calibrated to your measured muzzle velocities.