Re: Need some Quickload help
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fred_C_Dobbs</div><div class="ubbcode-body">Just kidding, dude. Actually, I was stalling while I could write this.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">...I assume it explains HOW to decide on exactly what your OBT is for your gun? </div></div>
Uh ......... no, not really.
Fortunately,
this guy does.
Here's his breakdown of optimum barrel times. And
here's his "how to."
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">Not going to spoil the suspense....
Q-is barrel length for OBT considerations measured from the breech face? </div></div>
RTFM, dude!
Barrel lengths are measured from the bolt face to the muzzle crown
Here's how Dobbsie does it. There's a lot of "my way" in here that has everything with how I do it and nothing in particular to do with OBT. But it works for me.
I tweak everything in QL I can reasonably measure. With a standard dial caliper and a 6x hand lens, you can do a surprisingly good job of measuring a bullet. Without the hand lens, the boattail is a beyotch. I find the OAL of most bullets is wrong in the QL db but the dimensions of the boattail tends to be right. Go figure. Don't forget to measure all the stuff I mentioned before. Measure a bunch and take averages.
I select the intended bullet and powder, then enter the heaviest charge weight I realistically can expect to use (if you use a charge that blows up your rifle, don't say I didn't warn you). Click calculate and note the predicted Barrel Time.
I consult the Optimum Barrel Time list for my length barrel and pick the next <span style="font-weight: bold">larger</span> number than QL's predicted BT (unless I get a perfect match). This will be my target OBT.
I adjust the charge weight in QL, click calculate and repeat until the calculated BT matches the target OBT. Chris Long says you only need to match the first two digits, which is fortunate because if you're only entering charge weights in tenths of a grain, it'd be pure blind luck ever to hit the OBT to the third digit.
The charge weight that produces a matching BT is my initial OBT charge weight. I load up enough test loads to confirm MV, chronograph them and average their velocities. At this juncture, I don't sweat it if ES looks high.
The next step is to adjust the selected powder's Burning Rate Factor and recalculate until the predicted MV matches my range data (the initial charge weight still should be there). There's a button to the left of the powder selection window that looks like a hand holding a pen. Click it and you'll be able to edit powder properties. BRF is the only one I've ever had reason to monkey with.
Above the "Apply & Calc" button is a button with a thermometer on it. Use this setting to enter the temperature during your range session. IIRC, the default temperature is 70°F. If you select certain powders -- like Varget -- it will tell you not to screw with temperature. When you change the temperature, QL adjusts the BRF to keep it in sync with all the other numbers.
The changes to powder properties are not permanent. They go <span style="font-style: italic">auf wieder bye-bye</span> the next time you select another powder (or the same one again). If you want them to stick, you'll have to create a custom powder file. I prefer just to jot down the new BRF in my log book.
Once I've tweaked BRF until the predicted MV matches my range data, I've got the new OBT charge weight. I record the new BRF and temperature in my log book and load up new test rounds at that charge weight.
Because this predicted MV is based on my guess at a max load, and because accuracy nodes are so far apart pressure-wise, this MV probably is the best I can expect from OBT. If it's not high enough to suit, I either abandon OBT or play around with bullets and powders to try to get on a faster accuracy node.
I can go three different ways with range session #2.
1. Worst case, my MVs will be off enough to make me doubt my BRF, or my ES will be so bad, I want a mulligan. In either case, I go home, check my QL data and work that load up again.
2. Or my MVs can be okay but the group sizes are too large to suit. When this happens, I use the OBT-predicted charge weight as the middle load for OCW testing. I started out routinely doing an abbreviated OCW at the second session but I found that my rifles -- well, all but one, anyway -- get along with OBT so well that the OBT-predicted load almost without exception also was the OCW. I'm lazy so as I grew more trusting of OBT, the number of OCW groups I shot kept dwindling until it shrank to ...just one.
3. Since I've grown trusting of OBT (and know the rifle I'm working with is cozy with it), all I want to see in the second session is a reasonable level of accuracy. If I get that, I go straight to adjusting seating depth. This is a great leap of faith because if I don't do OCW (or something similar), I'll never know how much untapped accuracy there might be in those surrounding charge weights. But I have gotten just that comfortable with OBT. Unless and until you reach that point, probably best you do OCW or a mini-Audette.
For the ADD crowd, here it is in checklist format:
1. Select your bullet and powder in the QL databases
2. Guess at a max charge weight and calculate. Note the calculated Barrel Time.
3. Select the lowest accuracy node time that's greater than the calculated BT
4. Adjust charge weight until the resulting BT matches the target OBT to two digits. If this charge is heavier than your starting weight, you've done something wrong.
5. Load and chronograph test loads at that charge weight
6. Tweak your powder's Burning Rate Factor until the resulting MV matches your range data
7. Record the new BRF and temperature
8. Load test rounds at the new charge weight
9. Test new loads by OCW or whatever method you consider suitable </div></div>
Awesome post, thanks!
