Spin drift?

[BravoKilo]

Was wondering if anybody here could comment on spin drift in regards to crossbow arrows?

Recently switched over to a Hawke XB30 compact scope and have been trying my damnedest to get everything perfect. One of the things I've been noticing is that I can get a perfect zero at 20 yards then when I start pushing out the distances to 30 and 40 yards, aside from the expected drop, I'm also getting a decent amount of drift to the right. Absolutely calm day so wind isn't the culprit. I know spin drift factors into distance rifle shooting and figure the same is applying to this case...?

Didn't actually measure the amount of drift but it's only an inch or so at 30 yards, and maybe 2" at 40 yards... still plenty good enough to take a deer down in the woods, I'm just being anal and wanting to shoot laser beams with this new setup Shooting BEA executioners, 2" blazers and 100gr. fieldpoints at the moment

[Masboy]

When mine is dead inline at 50yds on a calm day it is also inline at 20-30-40 an most time if not the crosshairs are not level unless your shooting the HHA .

[8ptbuk]

Has your scope been leveled on your crossbow ? Maybe canting the bow slightly ? Both will cause this.

[BravoKilo]

When mine is dead inline at 50yds on a calm day it is also inline at 20-30-40 an most time if not the crosshairs are not level unless your shooting the HHA .

I recently overhauled my setup a bit and am trying to narrow things down. Before when I had my old single red-dot sight on it, I didn't quite pay as much attention to any drift and attributed it to being a cheap red dot.

Phoenix bow. Aside from the Hawke XB30c, I picked up a new set of Vortex rings and lapped them last night. Also used bubble levels to make sure the crosshairs were level to the rail. Rings torqued down to manufacturer specs. Also have a new string and the BEA executioners are new to me also. Stopped using Lumenocks as I was getting too much drop compared to my other arrows (3+ inches at 30 yards, and even worse at 40).

Anything in particular that I should be checking? Any possible issue with the limbs being off center and causing this? Still wet behind the ears when it comes to any kind of bow tuning.

Thanks!

[BravoKilo]

Has your scope been leveled on your crossbow ? Maybe canting the bow slightly ? Both will cause this.

Scope was leveled. Canting was the next thing I was thinking. Will have to pay attention next time I'm shooting.

[_woods]

Maybe canting the bow slightly ?

This!

Highly recommend mounting a small bubble level somewhere on your bow. Will make a huge difference in accuracy and consistency at greater distance.

[Tom]

If your scope is level it is probably canting the bow.

Here is a suggestion:

when out shooting, with the setup your used to shooting, setup a string to hang down in front of the bow. Line the string up so that it is parallel to the vertical cross hair. This will help tell if the scope is level, Also it will show if your canting the bow when shooting.

Hope that works.

Tom

[BravoKilo]

Maybe canting the bow slightly ?

This!

Highly recommend mounting a small bubble level somewhere on your bow. Will make a huge difference in accuracy and consistency at greater distance.

Know there are quite a few options from the rifle community both scope mounted and rail mounted.

Looks like B-Square has a cheaper alternative than most others. Any other recommendations?

[Masboy]

I do alot of long range shooting an the longer the range the more tricky it gets. being level is very important to shoot inline for me. I not only level my crosshairs but also have my range stand level an also have my targets I shoot perfectly level an that helps me alot . I have a habit of canting my bow an found if I cant it to the left I shoot to the left an if cant to the right I shoot to the right. I think they say if your tillers off it shoot to one side? I,m no expert for sure but all my bows shoot inline at longer distance most times. I ,m sure others on here will help you that know more than I.

[_woods]

Any other recommendations?

Depends on how much you want to spend... I think Midway USA has a couple pages worth.
I went the cheap route and got this from Lancaster Archery.

[Onetimeonly x-->]

When I sight in with my XB-30 I try to get close to center at 20yds then shoot at 40yds and make right and left adjustments with the scope turret. Up and down with FPS ring. After my adjustments are good at 40yds (on target) the others 20,30,50yds tend to be good also.
Scott

[FNARSCOT]

Spin Drift is moot at these speeds and ranges I.M.O. As is Coriolis Effect Try this. Back up to max range. Smallest dot you can see.(aim small miss small) Off a bench, Seated, Bipod, Rear bag, Level ,Square to target. No wind. Take as much Human as you can out of the shot. Same arrow for every shot.(try to use an arrow that flys the same no matter where the cock feather is placed. With the same weight field point as your broad heads. Breath and Squeeze. Dial in for perfect center. Now go back and check your 20yd zero. Set up the same as you did at you max range. You will most likely be dead on. Now check all your other arrows. Repeat with Broad heads. Cull any gear that shoots different enough to matter. Chicken feathers/lucky sox /secret hand shakes are optional Full moons do help

[fuzzy]

...

[Kegbelly]

Were you hitting consistently to the right with the previous scope? Could be a scope/rings/alignment issue and you might need to adjust your zero accordingly.
Are you using a rest? That can make a difference when fine tuning. Do you shoot right handed? Most people if they pull a shot it tends to be in the direction of their trigger hand. At 20 yds it might not show up but at 40 it could. Not saying you're pulling, just thinkin out loud.
Have you spin tested your arrows? Variations in concentricity will be exaggerated at longer yardages. If every shot at 30 and 40 is consistently hitting to the right I'd vote for scope the tiniest bit out of level or limbs not level when you take the shot. If all else fails move it 1 click left and see where you're at at 20, 30, and 40, maybe split the difference, 1" off at 40 is still plenty good to take game. (but being a little OCD myself I know where you're coming from )

[nchunterkw]

I was recently reading a paper on arrow aerodynamics (yes, really) and one thing they looked at was arrow rotation. In the study, it took and arrow about 8 meters to come up to "full rotational speed", in which an arrow rotated 1 time for every ~~2 meters it traveled. Given that, an arrow rotated about 2500 degrees in 20 meters - which is only about 7 times. So I'm in agreement with FNARSCOT on this, that spin drift does not matter. Study was on vert bow arrows used in target shooting. 2" fletchings offset by about 0.5 degrees.