#Wind drift on arrow is insane

1 messages · Page 1 of 1 (latest)

turbid saffron
#

At 40 yard im getting like 3 feet of wind drift with the rth bow, ive never had to compensate more than a few inches at hunting distances irl.

pearl glen
#

I haven't tried calibrating the bows for ballistics yet, but the wind drift is all wrong for rifles. First, there is the issue of the scope reticle scales, as I've mentioned elsewhere. The Bushnell Elite Tactical DMR3 3.5-21x50 gets rescaled by a factor of 4, so whatever number you read off on the axes, multiply that by 4 to get the true MILS value. And if that is not bad enough, the wind deflection for bullets is too small, even with the corrected scale factor. It's as though they plugged the numerical value of the wind speed (in m/s) into a ballistics calculator that expects the wind speed in km/hr (so a 10m/s wind is 36km/hr). That makes a huge difference in the predicted wind drift - if I do this, then I can get the wind drift to agree with my measured values using HunterSense. One has to use a bullet with low BC and muzzle velocity, like a 22LR round, where it is clearly visible, but even for something like a 270 Win and a 10m/s crosswind, I've been able to measure the drift out to 1000m.

pearl glen
#

What is the wind speed and direction relative to your line of sight?
I ran a quick try with that bow with a 5 m/s crosswind - I'm seeing a drift of about 20cm at 50m.

turbid saffron
#

with a 10.9 m/s cross wind im getting 3.5mrads(as measured by the ffp reticle) of deflection. multiply that by 4 and we get 14. 14mrads is 54.6 inches at 100m, divide that by 2 because we are at 50m and it comes to 27.3 inches of wind drift at 50m. aka 69.3cm

#

If we get another hurricane this year ill go out and shoot in it to get some real world measurements, but im pretty confident that my real life setup (which only slings arrows at 295 fps compared to the bear rth advertised 335) will have less than 27 inches of drift at that distance. Im expecting somewhere between 16-20in with my slower bow and lighter arrow. i do feel like 10.9 m/s is a stiff wind on such a clear day and i have seen higher winds.

pearl glen
#

Which scope are you measuring with? Only the DMR3 uses the 4x scale factor.

#

also, if you are using the DMR3, the smallest subtensions are spaced 0.25 units apart, the next largest are 0.50 units apart, and the largest are 1.0 units apart. If you see a deflection of 3.5 units, that is waay off to the left or right along the windage axis, between the big 2 and the big 4 markings.
For the Steyr SSG M1 / .5mm-creedmoor/eld-x bullets, even in a 13.0m/s 90-degree crosswind, I only see an angular deflection of 0.333 units at 900m - that's just a bit more than the first 0.25unit subtension

turbid saffron
#

It is the dmr 3, and like I said, when aiming at the center of the target my arrows were sitting at 3.5 units, basically in the deers hind quarter.

Maybe I'll play around with it a bit more when I have the time.

pearl glen
#

I see, okay. I'll have to pop back to the range and try to wait for a stronger crosswind LOL

pearl glen
turbid saffron
#

There's a cat 3 hurricane in the forecast so if I get the chance I'm going to get some real world data as it moves in.

pearl glen
turbid saffron
#

I never got a chance to test when it would be safe, there were smaller thunderstorms in front of the hurricane that didn't bring any wind over 10mph (~5m/s), and I've been cleaning up ever since it blew through.

It knocked my barn down and took a tractor and an ATV with it. Our power is probably going to be out for at least a week.