QL and OBT

[savageshooter86]

Just curious -
When you adjust quick load to match the velocity of your powder/bullets, do the calculated OBT match your accuracy nodes seen on paper? I'm wondering how close QL and OBTs match actual accuracy nodes.

Thanks for any help.

 

[Jay Christopherson]

If you model your rifle correctly in QL (by that I mean, *all* the variables are correctly set and predicted velocities match your actual chronograph results at any given powder charge), then the OBT nodes will match your accuracy nodes.

Some will claim to be "between" OBT nodes, but my guess on that is simply that QL is not setup correctly. Like I said, when it's correctly setup, it's predictions will match your actual chrono results (with temps factored in), usually within +2-3 fps.

My Dasher model matches anywhere from 40º - 90º in terms of external temp (burn rate). It look a lot of data collection to dial in the model this closely. My .260AI model also matches QL predictions through a wide range, but it took about 300 rounds worth of data collection to get there.

I'm still dialing in my newer rifle(s).

 

[louielouie]

X2 - each lot of powder will have a different Ba than the sample QL used, each primer and the bearing surface length of the bullet all play a part - I even use http://www.accurateshooter.com/technical-articles/overbore-cartridges-defined-by-formula/ for adjusting the 'weighting factor' so if you haven't read http://www.accurateshooter.com/gear-reviews/test-quickload-review/ and then http://www.the-long-family.com/Tuning%20QL%20to%20achieve%20best%20results.pdf do that, and start gathering empirical data.

 

[savageshooter86]

thanks. That is what I was looking for.
**I'm not wanting the easy way,with no load workup, I just want to get a very good idea of the load window to test in. This way I do not waste as many components and not even be in the general area when testing.

If anyone on here would like to help me I would be more than happy for the help

 

[Jay Christopherson]

X2 - each lot of powder will have a different Ba than the sample QL used, each primer and the bearing surface length of the bullet all play a part - I even use http://www.accurateshooter.com/technical-articles/overbore-cartridges-defined-by-formula/ for adjusting the 'weighting factor' so if you haven't read http://www.accurateshooter.com/gear-reviews/test-quickload-review/ and then http://www.the-long-family.com/Tuning%20QL%20to%20achieve%20best%20results.pdf do that, and start gathering empirical data.

Good call on the weighting factor. It's usually the last thing I "dial in" to get the model dead on. It doesn't take much fiddling with that variable though.

 

[Jay Christopherson]

thanks. That is what I was looking for.
**I'm not wanting the easy way,with no load workup, I just want to get a very good idea of the load window to test in. This way I do not waste as many components and not even be in the general area when testing.

If anyone on here would like to help me I would be more than happy for the help

The first thing to do is to take all the static measurements. Be very accurate here. Barrel length (bolt face to muzzle exit), case H2O capacity, loaded round COAL, bullet length, case length. Then, pick a powder load that is a safe starting point. QL is typically conservative I have found, but best to start with manufacturers recommendations.

Then, go shoot over a chronograph. Then do it again. And again. And so on. The first two or three times, I might shoot the exact same load, but maybe at different times of the day (temp) to make sure my load is producing consistent numbers. It's not unusual (for me, anyhow) to see the barrel gain velocity, even with no change in load, over the first 100 - 150 rounds.

After I've gathered that data, I start to refine the model a bit, playing with the burn rate to match my chrono numbers. Once matched, I fiddle a little bit, maybe loading a half grain more or less, going out and shooting over a chronograph again to gather more data. Once I have those numbers, I can start to refine the burn rate even more, to match the powder load variation.

I generally don't shoot less than 10 shots of a given load over a chronograph (in the beginning).

And then it's just rinse and repeat. Once you get your model to about 90%, where the predictions might be within 20fps or so for each given powder load, you start to play with bullet weight and weighting factor. You don't want to change either by very much and really, you shouldn't have to at this point. Maybe a grain or two on the bullet and maybe a few percentage points on weighting factor.

 

[AP2020]

If you model your rifle correctly in QL (by that I mean, *all* the variables are correctly set and predicted velocities match your actual chronograph results at any given powder charge), then the OBT nodes will match your accuracy nodes.

Some will claim to be "between" OBT nodes, but my guess on that is simply that QL is not setup correctly. Like I said, when it's correctly setup, it's predictions will match your actual chrono results (with temps factored in), usually within +2-3 fps.

My Dasher model matches anywhere from 40º - 90º in terms of external temp (burn rate). It look a lot of data collection to dial in the model this closely. My .260AI model also matches QL predictions through a wide range, but it took about 300 rounds worth of data collection to get there.

I'm still dialing in my newer rifle(s).

I concur with my 260AI.

what "weighting factor" are you using?

Thanks

 

[Jay Christopherson]

On my .260AI, I used a weighting factor of .4, which seems to work well for ackley-ized rounds. With something like a 284 Shehane, with it's not-quite-Ackley 35º shoulder, I used .45. A steeper shoulder will keep more of the powder in the case during the burn, which equates to a slightly-closer-to-zero weighting factor. At least, as it was explained to me by someone who knows a lot about it.

I think 90% of all my fudging has been done between .4 and .5. In one case, I fudged into the high .3's because it fit the "real" data.

 

[AP2020]

Good.

I, too am using 0.40 as the weighting factor.

Water case capacity = 55.9 gr.