Anyone use Retumbo in QuickLoad calculations and want to share the Burn rate Factor Ba that you use? I think the default Burn Rate is waaay off.
QuickLoad & Retumbo
- Thread starter mtang45
- Start date
Don't have it for Retumbo but I can verify that the BA does need adjusting for some powders. In my 6.5x47 with RS Hunter QL has the BA set higher and it's showing velocities about a 100 f.p.s faster than actual magneto results.
Best thing to do is to chrono and adjust accordingly to match over a few different charge weights. Be sure you adjust your temperature too.
Best thing to do is to chrono and adjust accordingly to match over a few different charge weights. Be sure you adjust your temperature too.
Thanks for the info. QuickLoad has always been relatively close for me so this last experiment twisted my head a little. I am working on a load for a 7mm STW trying to hit an OBT of 1.39ms using a 180gr Berger and QuickLoad reported 79.1gr of Retumbo pushing it at 2888 fps, with the pressure in the yellow at 55937psi and well below the max of 66717psi. I tried those loads at the range last weekend and they were definitely hot, primers were flattened (not extreme but certainly getting close) and my chrony averaged 3095 for 4 shots; over 200fps faster than predicted.
I aborted the shoot and when I got home pulled out my old Sierra manual that sugested 75.3gr as a max load. I went to Hodgdon website and it says 74.5gr max. I thought perhaps the case volume was incorrect so I checked water capacity. I got 99.98 gr and the default in QL was 97.0. I adjusted it in QL and recalculated; now QL reports that I need 81.0 gr to achieve 1.39ms OBT and 2904 fps. There is no way I'm trying 81.0 gr after the pressure signs at 79.1
So next step is to adjust the burn rate but it will be more than just a tweek. With all the success I have had with QL, I'm wondering why this powder data is so far off.
Update: To get the 3095 fps I averaged on the 4 shots I had to bump the Burn Rate Factor to .442 from .337, QL now reports chamber pressure at 88951 psi and max is 66717
If I put your 0.442 Ba into QL, my safe 7SAUM load with 63grs of Retumbo is suddenly doing 85k pMax! So I don't think that adjustment is correct.
So what am I missing? I plugged in the Hodgdon max load and confirmed the Burn Rate to be close to .442 to achieve their published velocity.
I don't know sir, wish I did. QL is something of a mystery to me. It has steered me right in terms of starting loads and likely maxs, but I don't know the ins and outs. Sorry. Update this thread if you do figure it out.
A couple of other things to make sure might be :
1. That your not leaving any sizing wax left on the cases ( Its a long shot but I've seen it before )
2. Are you jambed into the lands ? If you are adjust your shot start pressure up to 7500, you may try adjusting this just to see if your velocities get closer anyways.
3. Make sure all the boxes you've filled in are correct....barrel, bullet dimension ( Check yours )
1. That your not leaving any sizing wax left on the cases ( Its a long shot but I've seen it before )
2. Are you jambed into the lands ? If you are adjust your shot start pressure up to 7500, you may try adjusting this just to see if your velocities get closer anyways.
3. Make sure all the boxes you've filled in are correct....barrel, bullet dimension ( Check yours )
If Retumbo is not correctly "defined" in QL, how do you know that Ba is the value that is wrong?
It could be a different value or several values.
Just because you managed to tweak a value and get the MV to match your scenario doesn't mean what you've changed accurately describes the characteristics of the Retumbo you're using.
The absurd chamber pressures predicted should be your first clue that your updated BA value is suspect.
It could be a different value or several values.
Just because you managed to tweak a value and get the MV to match your scenario doesn't mean what you've changed accurately describes the characteristics of the Retumbo you're using.
The absurd chamber pressures predicted should be your first clue that your updated BA value is suspect.
Here's another interesting read Mtang, Maybe there's some info to help you along in there.
http://www.snipershide.com/shooting...82927-quickload-underestimating-velocity.html
http://www.snipershide.com/shooting...82927-quickload-underestimating-velocity.html
Thanks for the link I'll read up and see if its enlightening. I have triple checked all the user input values and they are correct. The loads are doing a .120" jump so no extra jamming pressure. The odd thing is I can match Hodgdon velocity with their max load suggestion using the bumpped up burn rate.
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