Sweet range day, but a question...

Bear_Blade

Bear_Blade

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Been working with some 210 gr Matrix bullets, and Reloader 17. Been working with .308 Win, Lapua brass, Federal 210 primers, worked up from 45 grains of powder, up to 49 grains. Hit 2620 (average) with no pressure signs. Hit a couple accuracy nodes, but much slower than I would like. Got some monkeying around to do! Had a sweet spot at 47 grains. 5 shots 1 ragged hole at 100 yards, didn't physically measure it though.

Now for the question. I ran some data through JBM, and I am wondering which drag model to use. How do you select the correct one? G1, G4, G7? I am not schooled on this. Any help appreciated.
 
With boat-tail bullets with long noses (i.e. typical match bullets), G7 is the best fit to use.

Out to about 500 yards, you won't notice much if any difference between calculations done with G1 vs. G7 numbers. Both G1 and G7 data work quite well during the earlier part of the bullet's flight, when it is spending most of its time at 2000fps or faster.

The G7 drag curve is a better fit for speeds less than 2000fps. As your bullets get slower (800y, 1000y, 1200y etc), you'll find the predictions made from G1 data show more and more discrepancy, whereas the G7 data track better. It's a pretty small error though; G1 data for a .308 Win at 1000 yards is usually good to within one MOA or so. You need to do pretty careful testing in order to detect this error.
 
2620 with 210s is slow?? You're running about 75 fps faster than anyone was pushing 200s at F-Class Nationals, but the R17 would explain that. You might be able to find a node higher than this but if it's accurate why not fine tune here and preserve your brass and barrel?
 
Hey guys. Thanks for the pointers. Yes, there is a lot of work to do yet at increased distance with this load. As for my slow comment, I had one node at 2380, and another at 2460. I am shooting a 28" barrel, and with no pressure signs yet, and I mean none! I feel I can go a little higher, safely, and look for one more sweet spot. I am being optimistically cautious.

I ran initial loads starting at 45 gr, then .5 gr increments up to 49 gr's. From here I intend to go up in .2 gr increments, in hopes I hit one more node. I know at this point, some of my speed is due to the longer barrel, with the same pressure that would be slower in a shorter barrel, so using that to my advantage, I am having a hard time not to keep pursuing this. The idea of a 210 gr from a .308 Win, at or above 2700 fps, and a precision load to boot... I think that is an attainable goal.
 
Bear_Blade said:
How do you select the correct one? G1, G4, G7? I am not schooled on this. Any help appreciated.
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From what I understand G1s G7s etc are basically the difference between arc of flight. A G7 will shoot straighter then a G1, I think its rated by the ballistic coefficient or something like that, can someone chime in here and correct me if i'm wrong.
 
Bear

You can do what you are trying because I have. However, the 210's have specific accuracy nodes in which they fly well and you may get the velocity but not the accuracy so be prepared to back down a bit to stay within a node. Secondly, RE17 is very temperature senitive and most of the F-Class guys I know of have adandoned it's use for this reason. The Brits use it because where they shoot the temperature stays very stable throughout the year so it works for them. Try H4350 with WW cases. It gives almost the same velocity but is temperature stable. it is very accurate also.

Steve
 
.284 said:
Maybe back it to 300 yards or so to confirm your best reloads before crunching out a bunch.
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Hit the range again today with a friend to help him sight his hunting rifle. Brought along some tweaked loads, and pushed back to 300 yards.

Conditions, partly overcast, wind from 10 o'clock at 10kph light gusts to 25 kph, temp +2C.

So this range is only a 300 yard max facility. I fired 5, 5 round groups. Accuracy ranged from .92" vertical by 1.9" horizontal, to .45 vertical by 1.20 horizontal. Very pleased considering. I was shooting off a bipod, and am interested to see if there is much if any improvement off of bags, front and rear.

I'll get pics next time, promise.
 
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