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Hi, Ive been using QL as a quide to max pressure etc and then going to the range.

I know its not 100% but are there any indicators on the Pmax graph etc as to where accurate loads may be before fine tuning?

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  • 2 weeks later...

Used the OBT, sometimes it´s a hit, sometimes it´s a miss. Might be a result of inherent QL inaccuracy (ie OBT table might work, but QL won´t exactly hit the desired node) - but after some time, I believe it´s more a function of statistical probability of how many tries you need before you find that sweet spot. Every rifle has more than just one, and they´re not that far away from each other. That´s why the usual - a box of loads with .2grs difference - will sooner or later bring the same result.

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I had a look at OBT data etc and can only comment on my observation:

 

My most accurate load in 75gr Amax, .223, is not the fastest or hottest load going, 2608fps at 16.7C and 2577fps at 7C, it does however produce the tightest groups with same poi from load development, 100yd groups of 5 are circa 3/8 inch, sometimes a little bigger, rarely repeatably smaller.

 

My barrel is 22.5" and the load is 24grains of N140. The barrel time for this predicted by QL is 1.152ms, which tallies up with the data I found that had 7 OB times that may produce a very accurate load for a 22.5 inch barrel.

(I have omitted H2O case capacity and any other tweaks I have in QL to match chronographed MV etc)

 

If I wanted to try the next possible OBT, according to the the data, then I would have a drop in barrel time to 1.0394, now, this would mean that my charge weight would be a little too much for safety, I did have a play around with QL and other possible powders, but never got very far with this because I just want to shoot, not spend hours crunching data, especially since I have an extremely accurate load developed, why fix that which isn't broken.

 

Maybe its pure coincidence that my accurate load also matches barrel time data that predicts it should be an accurate load, but this would mean that my case capacity, my actual case length (which varies around 6 thou) or my COAL etc are all spot on. Change any of these in QL but keep the powder load the same, and it will result in a change in pressure and a change in barrel time, maybe it will make my accuracy suffer aswell? this I don't know as Im not changing anything to wreck my accuracy.

Have fun with it though.

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