Spin drift question

Talk with other Shiloh Sharps shooters.

Moderators: Kirk, Lucinda

Post Reply
Aviator
Posts: 427
Joined: Mon Sep 03, 2018 8:06 pm

Re: Spin drift question

Post by Aviator »

Distant Thunder:
That looks like what I would try.
It may need to be a little less shim than that, depending on the profile of the bottom of your sight base. It depends on just what the lines of contact are between the sight base and the tang, which could be smaller than the outside width of the sight base.

In any event, it of course ends up being an approximation, as spin drift is not a linear function. But the closer you are to the ball park, the easier is will be to deal with reversals.

I need to give a little thought to whether a similar thing could be achieved by tweaking the cant of the crosshairs of a scope, with respect to the rear scope mount travel. I suspect it would be difficult to make that work out reliably.

Steve
User avatar
Distant Thunder
Posts: 882
Joined: Sun Apr 09, 2006 11:46 am
Location: NE Wisconsin

Re: Spin drift question

Post by Distant Thunder »

desert deuce wrote: Tue Feb 16, 2021 12:16 am I just took an aluminum Coke can, a regular pair of scissors and cut a shim and placed under the right edge of the rear sight base on my Hepburn.

No micrometer, no chalk and no axe.

Why? Because that is what Dan'l told me would work. So I did it. Shim is still there. Guess it works OK.

And it took you 10 pages to say that why? :x

:lol: :lol: :lol:
Jim Kluskens
aka Distant Thunder
Aviator
Posts: 427
Joined: Mon Sep 03, 2018 8:06 pm

Re: Spin drift question

Post by Aviator »

One other clarification that I forgot to put in my last post:
Of course the rear sight alignment needs to be referenced to the level that is mounted on your rifle.
User avatar
Distant Thunder
Posts: 882
Joined: Sun Apr 09, 2006 11:46 am
Location: NE Wisconsin

Re: Spin drift question

Post by Distant Thunder »

Steve,

For some reason it seems more reasonable with a scope to just know the correction for each yardage, write 'em down and dial 'em in when you start out at each yardage. That's probably because my tang sight has a zero in the middle of the windage vernier and I set that as my no wind zero. With my DZ mounts, and MVA mounts too, the no wind is just somewhere near the middle of the windage travel and I have it written down.

Now that I think about a scope is much easier to set up. With a tang sight I find that I'm now trying, struggling, to set it up for my no spin zero! :?

It's time to let a little dust settle on this one before I pick a card! :roll: Any card!
Jim Kluskens
aka Distant Thunder
gunlaker
Posts: 2764
Joined: Tue Jun 23, 2009 6:16 pm

Re: Spin drift question

Post by gunlaker »

Distant Thunder wrote: Tue Feb 16, 2021 7:37 am Steve,

For some reason it seems more reasonable with a scope to just know the correction for each yardage, write 'em down and dial 'em in when you start out at each yardage. That's probably because my tang sight has a zero in the middle of the windage vernier and I set that as my no wind zero. With my DZ mounts, and MVA mounts too, the no wind is just somewhere near the middle of the windage travel and I have it written down.

Now that I think about a scope is much easier to set up. With a tang sight I find that I'm now trying, struggling, to set it up for my no spin zero! :?

It's time to let a little dust settle on this one before I pick a card! :roll: Any card!
I do the same as you when using DZ mounts. A scope makes it much easier. If you have a MVA front mount you can dial the spin drift on it just like on a windgage front which is what I do on my .45-90 with MVA Creedmoor mounts.

Chris.
User avatar
Distant Thunder
Posts: 882
Joined: Sun Apr 09, 2006 11:46 am
Location: NE Wisconsin

Re: Spin drift question

Post by Distant Thunder »

Chris,

I hear ya! It's that cotton pickin' zero on the tang sight that makes life difficult! If not for that I'd run it like my scopes and just write down the elevation and windage setting for each yardage and be happy. I'd sleep better at night too, Steve! :x
Jim Kluskens
aka Distant Thunder
Kurt
Posts: 8428
Joined: Wed Oct 12, 2005 10:28 pm
Location: Not Far enough NW in Illinois

Re: Spin drift question

Post by Kurt »

Spindrift has never entered my mind. My sights are set with a no wind zero and most matches you have a few sighter shots and from there is the ability to make the wind calls to stay on center.
At the gong shoots it's more or less you and your rifle and the first shot fired is for score. This is where trigger time with your rifle comes into play learning what your rifle and your ability will be.
Most generally my first shot is on target unless I miss the conditions. Is it really to cant your sights because how close can you hold your rifle with out a natural cant and that front sight level sometimes gets to hard to see when the sun glare is a factor or your ability to see it well enough to see if the bubble is centered. With that short length that vial is resting in the dovetail .005-010" that bubble is off center will erase the set spin drift tilt on the sight.
The reason a dog has so many friends is because he wags his tail instead of his tongue.

"Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery"Winston Churchill
bruce m
Posts: 3350
Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: Spin drift question

Post by bruce m »

i was going to pm this to jim, but then thought all who have been following this might find it interesting.
here are the jbm figures for jims 45 cal rifle and load.
yards moa
100 0.3
200 0.9
400 1.2
500 1.5
600 1.9
700 2.2
800 2.6
900 3.0
1000 3.4
and for his 44
100 0.3
200 0.6
300 0.9
400 1.2
500 1.6
600 1.9
700 2.3
800 2.7
900 3.1
1000 3.5
bruce.
ventum est amicus meus
bruce m
Posts: 3350
Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: Spin drift question

Post by bruce m »

i was going to pm this to jim, but then thought all who have been following this might find it interesting.
here are the jbm figures for jims 45 cal rifle and load.
yards moa
100 0.3
200 0.9
400 1.2
500 1.5
600 1.9
700 2.2
800 2.6
900 3.0
1000 3.4
and for his 44
100 0.3
200 0.6
300 0.9
400 1.2
500 1.6
600 1.9
700 2.3
800 2.7
900 3.1
1000 3.5
bruce.
ventum est amicus meus
User avatar
Distant Thunder
Posts: 882
Joined: Sun Apr 09, 2006 11:46 am
Location: NE Wisconsin

Re: Spin drift question

Post by Distant Thunder »

Thanks, bruce.

I'm not sure what other shooters will gain from it. Interesting comparison between the .44-77 and the .45-70 both with paper patch bullets of course. Nothing big enough to show up on the target between the two. Eventually I'll have enough info to compare the two cartridges for elevation settings as well.

If I had to put a number on the spin drift of my .45-70 I would have said 3 MOA. That's just based on what I've noticed in my windage setting over the past few years. Now I'll try to adjust for it at least somewhat close.
Jim Kluskens
aka Distant Thunder
bruce m
Posts: 3350
Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: Spin drift question

Post by bruce m »

here is same for my 40/72 with 13 twist and a 1.5" long bullet at around 1300 fps.
100 0.4
200 0.7
300 1.0
400 1.3
500 1.7
600 2.0
700 2.4
800 2.8
900 3.2
1000 3.6
as you can see the 45 at 18 twist has less than the 44 at 17 twist has less than the 40 at 13 twist.
of course we are not including time of flight in this, but the 40 is a little faster than the other 2.
0.1 moa is 1" at 1000 yds so probably not worth worrying about on that basis, but adjusting sights to that level is nigh on impossible.
3 moa at 1000 yds is over 30" on the target so it matters.
if you are just a shot chaser and don't care about missing the first sighter spindrift is not an issue.
just for interest sake, what do some of you believe your windcall ability is in moa?
i think jim must have good grouping rifles shot well to pick up on spindrift like he has.
i have watched long range shooters complaining that the flags read differently from one direction than the opposite.
guess what their problem is?
look out when he nails this one!
bruce.
ventum est amicus meus
User avatar
Distant Thunder
Posts: 882
Joined: Sun Apr 09, 2006 11:46 am
Location: NE Wisconsin

Re: Spin drift question

Post by Distant Thunder »

I see this spin drift thing as being another piece of the puzzle that helps me better understand what I've been seeing at 1000 yards and why it's there. That can't be a bad thing. Even if it just helps me better think through corrections for a unknow value of a reversal it will put more points on my score sheet. I've shot in many matches where the winner is decided by 10 points or less, sometimes much less.

Experience gained by shooting matches has taught me how to make better decisions, understanding what my bullet is doing on it's way to the target will only add to that. I think my rifle will be better set up this year than ever before by taking into consideration spin drift and that will help me be a better shooter.

If I hadn't noticed the windage always being somewhat more left than I thought it should be from what I could see in the conditions I won't even have pursued this spin drift like I have. There were some very good posts early on in this thread that I connected with what I've seen and wonder about. Now I think I understand what has been going on. It's worth taking steps to correct for it, I think.

My thanks to all who contributed to this subject in a meaningful way.
Jim Kluskens
aka Distant Thunder
COBPTR
Posts: 279
Joined: Thu Aug 04, 2011 9:18 am

Re: Spin drift question

Post by COBPTR »

I hope all of you have a sight radius of exactly 34.3839541547 inches. Otherwise, it is all for naught when figuring spin drift in MOA. :)

Robert G.
When the going gets weird, the weird turn pro.
gunlaker
Posts: 2764
Joined: Tue Jun 23, 2009 6:16 pm

Re: Spin drift question

Post by gunlaker »

COBPTR wrote: Tue Feb 16, 2021 8:42 pm I hope all of you have a sight radius of exactly 34.3839541547 inches. Otherwise, it is all for naught when figuring spin drift in MOA. :)

Robert G.
I'm pretty close but I'm in Canada so mine is metric :lol: :lol:

Chris.
bruce m
Posts: 3350
Joined: Tue Aug 04, 2009 5:25 am
Location: australia

Re: Spin drift question

Post by bruce m »

there's the problem robert.
when you change the angle of the staff for long range, the radius changes.
bruce.
ventum est amicus meus
Post Reply